AV3Sif?

Io

CONS/2062-1

MEASUREMENTS ON INSULATING MATERIALS AT

CRYOGENIC TEMPERATURES

Annual Report

1976

Work performed under Contract No. E(49-1)-3800

National Bureau of Standards

Washington, D.C.

ENERGY RESEARCH AND

DEVELOPMENT ADMINISTRATION

ii

Division of Electric Energy Systems
NOTICE

This report was prepared as an account of work sponsored by the United States Government. Neither the United States nor the United States Energy Research and

Development Administration, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any

legal liability or responsibility for the accuracy, completeness or usefulness of any

information, apparatus, product or process disclosed, or represents that its use would not

infringe privately owned rights.

This report has been reproduced directly from the best available copy.

Available from the National Technical Information Service, U. S. Department of

Commerce, Springfield, Virginia 22161

Anderson, W. E., Davis, R. S., Mopsik, F.

I., Kryder, S. J., Khoury, F., Colson, J.

P., Bolz, L. H., Measurements on insulating

materials at cryogenic temperatures. Annual

Report, Energy Research and Development

Administration Energy Conservation Report

CONS/2062-1, Part I and Part II, 155 pages

(Available from the ^National Technical

Information Serviced, Springfield, VA Sept.

1976)

Price: Paper Copy $6.00 (domestic)

$8.50 (foreign)

Microfiche $3.00 (domestic)

$4.50 (foreign)

7-/0

511

J7/>^ i
CONS/2062-1

Distribution Category UC-95b

MEASUREMENTS ON INSULATING MATERIALS

AT CRYOGENIC TEMPERATURES

ANNUAL REPORT

PART I WILLIAM E. ANDERSON

RICHARD S. DAVIS

PART II

F. I.MOPSIK AND S. J. KRYDER

F . KHOURY, J. P. COLSON AND L.H.BOLZ

UNITED STATES DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

WASHINGTON, D. C. 20234

DATE PUBLISHED - SEPTEMBER 1976

PREPARED FOR THE ENERGY RESEARCH AND

DEVELOPMENT ADMINISTRATION

OFFICE OF CONSERVATION

DIVISION OF ELECTRIC ENERGY SYSTEMS

UNDER CONTRACT NO. E(49-18)-2062

PART I

DISSIPATION FACTOR MEASUREMENTS MADE IN THE

ELECTRICITY DIVISION ON INSULATION AT

HIGH VOLTAGE AND CRYOGENIC TEMPERATURE

Interim Report for the period

Nov. 197A-Sept. 1976

by

William E. Anderson

High Voltage Measurements Section

and

Richard S. Davis

High Voltage Measurements Section

l
TABLE OF CONTENTS

ABSTRACT 1

SUMMARY 2

INTRODUCTION 6

EXPERIMENTAL 7

Sample Holder 8

Cryostat 11

Standard Capacitor 13

Current Comparator Bridge 17

RESULTS 2k

WORK IN PROGRESS: CORONA DETECTION SYSTEM 30

Electronics 32

Data Analysis 3^

Progress 36

CONCLUSION 36

REFERENCES 38

BIBLIOGRAPHY 39
ABSTRACT

This report details progress made to date on developing instrumentation and

measurement methodology for studying high-voltage dielectric losses at cryogenic

temperatures . The work described has been done in support of ERDA- funded ac

superconducting transmission line projects at Brookhaven National Laboratory (BNL)

and the Linde Division of the Union Carbide Corporation (UCC-Linde). Dissipation

factor measurements have been made at a temperature of 4.2 K and at stresses up to

40 kV/mm. Care has been taken to insure that errors in dissipation factor measurements

-6

are less than ±1 x 10 . Sample dielectrics have included polymer tapes of interest

to BNL and epoxy spacer material of interest to UCC-Linde. When dissipation factor

measurements are made at high voltage, losses at sample interfaces become important.

Flexible superconducting cables are designed to have many layers of coaxially wound

plastic tape serving as the insulation. The spaces between tape layers will be

impregnated with helium at pressures up to 1.5 MPa. Plans to investigate highvoltage dielectric losses under these conditions are discussed including a technique

for measuring partial discharges using pulse-height analysis.
- 2-

SUMMAEY

The contents of the following report are here summarized for the convenience

of the reader. The report covers the period from November 197^ through June 1976.

In November of 197^- the High Voltage Measurements Section in the Electricity

Division of the Institute for Basic Standards began a project sponsored by the

Energy Research and Development Administration to study ac losses in dielectrics

at cryogenic temperatures. The ultimate goal of the project is to provide

dissipation factor and corona data under the proposed operating conditions for

Brookhaven National Laboratory's (BNL's) ac superconducting power transmission line

(AC SPTL). Because of BNL's urgent need for engineering data and the extra time

involved in designing and constructing a supercritical cryostat, initial efforts

have been toward providing 60-Hz dissipation factor data of polymer films at U.2 K

and atmospheric pressure. These measurements, although only a first step, do

provide valuable data at the electrical stresses proposed for the AC SPTL.

Preliminary dissipation factor measurements on layers of polymer films suggest

that losses at interfaces may dominate the intrinsic dielectric losses of the

polymer films. These interfacial losses are probably due to partial discharges.

We have begun the design and development of a system to study these partial discharges

using the pulse height analysis technique.

Besides the measurements on the polymer tape insulation for the BNL SPTL, we

have provided Union Carbide Corporation, Linde Division (UCC-Linde) with dissipation

factor values for epoxies used as spacers in their helium-insulated cable.

In order to accomplish the necessary measurements, a cryogenic facility was

built in the High Voltage Measurements Section. This consisted of a conventional

glass double-dewar system. High voltage was introduced into the cryostat

by means of a vacuum-insulated bushing which was discharge free to 8.5 kV. All

experiments were performed with the sample material immersed in liquid helium
-3-

at atmospheric pressure. Size limitations of the dewar necessitated the use of

2

a small (10 cm

-

) parallel-plate capacitor as sample-holder.

Electrical measurement of dissipation factor was made by comparing the loss

of the sample dielectric with that in a commercial compressed-gas high-voltage

capacitor. This comparison was made with sufficient accuracy by using the NBS

current comparator bridge. Samples formed the dielectric of a three-terminal

stainless-steel capacitor whose design incorporated ASTM recommendations for

dissipation factor measurements. Due to the small dissipation factor allowable

-6

in superconducting cable insulation, an accuracy of ±1 x 10 was desirable in

our measurements. Success in this was achieved through a meticulous absolute

determination of the dissipation factor of our compressed-gas high voltage

capacitor

As an initial consistency check we measured the dissipation factor of liquid

helium at ^.2 K. At a stress of 1.5 kV/mm the 60 Hz dissipation factor was

—6

(0.3 ± 0.7) x 10 . This is consistent with the fact that liquid helium has

no intrinsic loss mechanisms at power frequencies.

No attempt was made to measure a representative sample of polymer tapes.

Only those tapes that proved to be among the most promising from mechanical tests,

low-voltage electrical tests, or economic considerations were sent to us by BNL.

Each sample was measured at least twice to test repeatability and prevent erroneous

values caused by the occasional cracking of some materials.

General comments can be made about the results of these measurements. The

polyethylenes and polypropylenes both have dissipation factors considerably less

-6

than 30 x 10 (upper limit for BNL SPTL) at design stresses of the order of

20 kV/mm. These films along with the polyamide sample, however, have poor

mechanical properties at liquid helium temperatures. The polycarbonate and

polysulfone films are much better mechanically but have dissipation factors in the
-k-

-6

range of 50 to 100 x 10 .An attempt by the manufacturer to improve the

dissipation factor of one of these materials (green polysulfone) by reducing the

concentration of sodium impurities was somewhat successful.

While the dissipation factor of most of the materials increases slightly

with increasing voltage, both of the polyether-sulfone samples measured have

a negative voltage coefficient . We do not know whether the cause of this is related

to the well-understood behavior of oil-impregnated paper-insulated capacitors.

The dissipation factor of the epoxies submitted by UCC-Linde were an order

of magnitude larger than the polymer tapes but below the 500 x 10 ^ limit for the

UCC-Linde SPTL. Sample preparation (including catalyst concentration) may account

for the varying results on identical materials of differing thicknesses. The

apparent increase of the dissipation factor with sample thickness, however, may

be a real effect resulting from the increased probability of voids or other defects.

We found it impossible to make these measurements without coating the electrodesample interfaces with paraffin oil. Presumably this procedure suppresses corona

at the interfaces. It has been our experience that when samples have not been

coated with paraffin oil prior to insertion into the sample capacitor, the measured

dissipation factor exhibits a strong voltage coefficient. Presumably this, in part,

is caused by the presence of helium bubbles. The corona might be suppressed in

supercritical helium. This point will be elucidated by our measurements in the

coming year.

To examine further the effects of paraffin oil on various interfaces, we

studied several stacking arrangements of polypropylene films. We measured the

dissipation factor of three-sheet stacks of this material with and without paraffin

oil on the various interfaces. As the number of uncoated interfaces increases, the

positive voltage coefficient of the dissipation factor increases. This effect may

be suppressed under the supercritical conditions of BNL's proposed SPTL. It is

therefore our intention to continue our measurements in an apparatus which will

operate at these conditions.
-5-

The results reported to date are the outcome of measurements to determine

dissipation factors in single-layer samples at high electrical stress. The actual

design of BNL's SPTL calls for wrapped polymer tape insulation impregnated with fluid

helium. In such a system, the occurrence of corona between tape layers or "butt gaps

may dominate other loss mechanisms. Corona could also prove to he the most important

cause of insulating aging in a regime in which "normal" thermal aging is suppressed.

We have, therefore, designed and begun construction of a corona measurement system.

In order to glean more information that can normally be obtained from a

conventional corona detector, our system will use a technique recently borrowed

from the nuclear physicists—pulse height analysis. With this method the corona

spikes are sorted by peak amplitude. The result is a histogram of the number of

spikes of a particular amplitude versus amplitude. The evolution of the profile

of this histogram as a function of time will yield information concerning changes

in the dielectric. A particular profile might, for example, indicate a large void

or impurity exists in the dielectric. Parameters such as applied voltage, temperature,

frequency, and pressure can be varied in order to study their effect on this profile.

The final profile for each experimental run will be stored on a floppy disc for

future comparisons. The minicomputer used to sort the data will also be available

for data manipulation such as finding the total energy content of the corona — the

integral of the histogram. The individual circuits have been breadboarded and tested

but the total system has not yet been assembled.

Future work will involve extending our dissipation factor measurements to

conditions proposed for the AC SPTL. Measurements will be made on coaxial samples

at temperatures from 7 to 9 K and pressures from 1 to 1.5 MPa (10 to 15 atmospheres).

The corona measurement system will be completed which will enable simultaneous

corona and dissipation factor measurements. Corona inception level measurements

on single layer and multi-layer polymer films will also be initiated.
- 6-

INTRODUCTION

In November of 197^- the High Voltage Measurements Section -in the Electricity

Division of the Institue for Basic Standards began a project sponsored by the

Energy Research and Development Administration to study ac losses in dielectrics

at cryogenic temperatures. The ultimate goal of the project was to provide

dissipation factor and corona data under operating conditions proposed for an ac

superconducting power transmission line (AC SPTL) at Brookhaven National Laboratory

(BNL). In order to provide useful data as soon as possible, initial efforts have

been toward measurement of the dissipation factor of polymer films at k.2 K and

atmospheric pressure. The engineering questions to which we sought answers are:

which polymer insulating tapes have the lowest intrinsic ac losses at cryogenic

temperatures; and are these losses a function of electric field amplitude,

particularly up to design stresses proposed for the AC SPTL? Later in the project,

we also began measuring ac losses of epoxies. The epoxy measurements are useful

to the AC SPTL program at the Linde Division of Union Carbide Corporation (UCC-Linde).

The projects at BNL and UCC-Linde are both funded primarily by ERDA.

The respective interest in polymer tapes by BNL and epoxies by UCC-Linde

reflects their different cable designs. BNL's cable will be flexible. The

insulation contemplated is analogous to conventional oil-impregnated paper cables

in that helium plays the role of oil and a suitable polymer tape the role of paper.

The UCC-Linde cable is a rigid or pipe-type cable which uses helium as the electrical

insulation and epoxy spacers to position the conductor in the helium.

As our work progressed, it became increasingly clear that interfacial losses,

either between layers of insulation or at electrode surfaces, can exceed the

intrinsic dielectric losses of polymer tapes. The interfacial losses are probably

due to partial discharge. Therefore we have undertaken the design of a corona

measuring system which will, through the use of pulse height analysis, provide

more information than can be gleaned by using commercially available devices.
-7-

This report covers the period from November 197^- through June 1976. It is

divided into three major sections: Experimental, Results, and Work in Progress.

The first section establishes the theoretical basis and describes our equipment

for making accurate dissipation factor measurements. Also included as an appendix

is a bibliography of useful references we have accumulated since undertaking the work

reported here.

Other work not covered in this report included the presentation of papers

at the 1975 Conference on Electrical Insulation and Dielectric Phenomena held in

Gaithersburg, Maryland and at the 1976 IEEE International Symposium on Electric

Insulation held in Montreal, Canada. Also the equipment used by BNL to measure

dissipation factor was calibrated in situ by NBS personnel.

The principal investigators for the work reported below were William E. Anderson

and Richard S. Davis, both physicists in the High Voltage Measurements Section of

the NBS Electricity Division. Administrative and scientific support were provided

by Oskars Petersons, Chief of the High Voltage Measurements Section and Barry N. Taylor,

Chief of the Electricity Division. Eric D. Sims, a technician, also worked part-time

on this project. The ERDA program manager is Alvin S. Clorfeine.

EXPERIMENTAL

The power, P, dissipated in a transmission cable due to dielectric heating

follows the relation

p cc f v^ e ' tan 6 (l

)

where f is the power frequency and V the operating cable voltage. In a superconducting transmission cable where refrigeration efficiency is low, all sources

of heat generation must be kept as small as possible. The reduction of P to an

acceptable value can only be accomplished by minimizing the product of c' tan 6

where c* is the real part of the dielectric constant e = e' + je" and tan 6 = e"/e',

the dissipation factor. Since e’ is about 2 to 3 for all polymers being considered

for the dielectric in a superconducting transmission cable, tan 6 is restricted to
-8-

a value of less than 30 x 10 . ’ This number is a rough figure of merit based

on the economics of cable refrigeration.

Measurements of the dissipation factor of various polymer films under high

electrical stress and at cryogenic temperatures are necessary in the search for a

suitable dielectric. Since the design stress for the superconducting transmission

cable is about 10 MV/m, measurements at voltages in the range of 2 kV to 5 kY for

samples of the order of 100 ym thick are needed. A total measurement uncertainty

of about ±1 x 10 ^ is required for meaningful comparisons of the materials.

The sample to be measured is placed between the electrodes of a parallel-plate

capacitor. The capacitor is inserted into a cryostat which is filled with liquid

helium. The current in this capacitor is then balanced against the current in a

compressed-gas standard capacitor using a current comparator bridge. This measurement

yields both s’ and the dissipation factor. Each component of this measurement system

will be described in detail.

Sample Holder

The sample holder consists of the two plates forming the parallel-plate

capacitor a the dielectric of which is the material to be measured. The stainless-s'teel

electrodes are shown in Fig. 1. The bottom plate consists of an active (inner)

electrode and a guard ring. These two electrodes were epoxied together then lapped

-3 2

and polished. The area of the active electrode is 1.05 x 10 m resulting m the

following relation between capacitance C and thickness d (in ym) of the dielectric:

C - 9-29 x 10^ (e'/d) picofarads . (2)

Typical thicknesses of the sample dielectric range from 25 ym to 125 ym so that

the capacitances to be measured are in the range of about 100 to 1000 pF (remembering

that e ' 2 or 3 )

The capacitor is held together with two polytetrafluoroethylene plates using

nylon screws and nuts with phosphor-bronze springs as shown in Fig. 2. During the
- 9- TOP ELECTRODE

BOTTOM ELECTRODES

FIG I. ELECTRODES
NYLON

BOLT

-10-

SAMPLE

HOLDER

ASSEMBLY
-11-

actual measurement the top electrode Is energized and the resulting current from

the inner active electrode is sent to the current comparator "bridge via a coaxial

cable. The outer shield of this cable is connected to the guard ring on one end

and to ground at the bridge.

Cryostat

The cryostat is shown in Fig. 3. The I.D. of the inner glass dewar is 11 cm

with a usable height of 1 m. A high-vacuum feedthrough 10

-

^ Pa) terminated at

both ends by commercial ceramic bushings (rated at 8.5 kV rms ) is used to get the

high voltage below the liquid helium level. This is necessary because gaseous

helium has poor breakdown characteristics (several times worse than air). A

stainless steel shielded, coaxial cable brings the signal out of the liquid helium

to the top of the cryostat. The total resistance of the leads running from the

capacitor to the bridge is less than 1 ft. At 60 Hz, this resistance would cause an

-6

added dissipation factor of 1 x 10“ in a 2600 pF capacitor. Since the capacitances

of all samples measured in this report are substantially less than this, the lead

resistance is seen to have a negligible effect on the measurement of dissipation

factor

A typical measurement requires about 5 to 6 liters of liquid helium allowing

from 3 to U runs per 25 liter supply dewar. The helium will stay in the croystat

for several hours, if necessary, although most measurements are completed in less

than an hour. The time for the cryostat to go from room temperature to h.2 K and

back to room temperature is about 20 hours which allows daily runs.

Since the dewars are constructed of glass, no attempt has been made to measure

the dissipation factor as a function of increasing helium pressure. Also in these

measurements the sample is immersed directly in liquid helium while in the measure4 5 ments of others ’ the sample is in a vacuum.
-12-

FIG. 3 CRYOSTAT
-13-

Standard Capacitor

Since the dielectric properties of the sample are obtained by electrically

balancing the current in the sample capacitor with the current in the standard

capacitor, a knowledge of the properties of the standard capacitor is essential

for this measurement. A 100 pF compressed-gas (nitrogen) capacitor is used for

the standard. In the majority of high voltage measurements this type of capacitor

can be assumed to be lossless. (Commercial capacitors generally claim a dissipation

—6

factor of "less than 10 x

10~ "). In our measurements, where a total uncertainty

of ±1 x 10

-

^ is necessary, the dissipation factor must be accurately measured. The

current comparator bridge which will be described in the next section has the

capability of measuring relative dissipation factors to better than ±1 x 10 ^ but

the absolute dissipation factor of the standard must be known in order to determine

the dissipation factor of the material being measured. The dissipation factor of

our standard capacitor was measured by John Q. Shields of the Absolute Electrical

Measurements Section, Electricity Division, NBS. A brief discussion of how this

was done° follows.

A guard ring capacitor with variable plate separation is placed in one arm

of a transformer ratio arm bridge and the standard capacitor to be measured in the

other. Successive relative dissipation factor balances between the variable

capacitor and the standard capacitor with auxiliary capacitors in parallel with

it are made. Since the relative dissipation factors between the standard

capacitor and each of the auxiliary capacitors can readily be measured, then

the relative dissipation factor between the standard and the variable-plate

capacitor at several settings will be known. If the dissipation factor for

the variable plate capacitor is caused only by a surface film, a plot of the

relative dissipation factor versus capacitance should be on a straight line as

will be shown below. The guard-ring capacitor with electrode spacing, d, and

film thickness, t, is shown in Fig. Ua. This capacitor can be represented by an ideal

capacitor, , in series with a lossy capacitor with capacitance, C^, and parallel
-IhC.

FIG. 4 ELECTRODE FILM CONTRIBUTION TO D. F.
-15-

resistance, R , Fig. 4b. This series combination can be represented as in Fig. 4c

by an ideal capacitor, Cq, in parallel with a resistor, R .

where

and

From ( 4 ) , ( 5 ) , and ( 6 )

,

Y o

Y Y

1 2

L + Y,

Y

1 = ^1

Y

2 = 1/R2 + jmC2

Y

o = 1/Ro + j“c o

*

(3)

(4)

(5)

( 6 )

Y

Q = (1 + jmC

2

R

2 )/(l + ju)R2

(C

± + C

p

) )

or

Y

o

u

2

C

1

2

Eg + jwCg [1 + u

2

C

2 Eg

2

(Cg + Cg)

]

? ? 2

i + o) r

2

(c

x + c

2 r

Using (6) and (8)

R

o

? ? 2

1 + 0i R

2

(C x + C

2

)

2 „ 2 „ “

°1 R

2

and

C

Q = C

1

[1 + a) 2

C

2

R

2

2

(C

1 + C2

)]/[l + a) 2

R

,

2

(C

± + C

2

) 2

]

The dissipation factor, D.F.

,

is equal to (go CqRq)

- '*'.

D.F. = go Cx R

2 /[l + go 2

C

2

R

2

2

(C

x + C

2

)] .

( 7 )

( 8 )

(9)

( 10 )

( 11 )
-16-

where

C

1 d - 2t ( 12 )

ana

(13)

assuming an area. A, and permittivity for the film.

Since t << d or C_^ <<

D.F. = w R

2

e Q

A/[(d - 2t) (l + u) 2

C

2

R

2

)] (lk)

or

(15)

where for a particular frequency K is a constant independent of plate spacing.

The film thickness t is much less than the electrode spacing so (15) can he

further approximated

Therefore, if the dissipation factor is caused by surface films, the D.F. should

vary inversely with the electrode separation, d, and hence be proportional to the

capacitance. A plot of relative dissipation factor for the variable capacitor versus

capacitance should be on a straight line. The intercept of this line with the

dissipation factor axis represents the relative dissipation factor for infinite

electrode separation and, therefore, the dissipation factor of the standard capacitor.

The fact that the points do lie on a straight line supports this model.

A portable standard capacitor was calibrated in this fashion and found to have

-6 -6

a 60-Hz dissipation factor of -1.1 x 10 with an uncertainty of ±0.3 x 10 . Our

-6

compressed-gas standard capacitor had a relative dissipation factor of 2.9 x 10

with respect to this portable standard or an absolute dissipation factor of

DF £ K/d . (16)
-17-

1.8 x 10

0

± 0.5 x 10

6

.

The negative dissipation factor, seemingly worrisome, is easily explained.

To see how this is possible, consider Fig. 5* The three-terminal measurement of

a guarded lossless capacitor, C , is shown in Fig. 5a. C„ and/CT are the capacitances

formed by the guard and the high and low voltage electrodes . In a bridge measurement

,

the low voltage side is grounded. In this case, the short-circuit transfer admittance

of the circuit shown in Fig. 5a is y

^ = jwC

s

. Now suppose, as in Fig. 5b, the

capacitor's construction is flawed by loss in a common ground return. This frequencydependent mechanism is represented by a resistance, R. If l/Rto is large, compared

to both Ch. and CT , then y, 0 ^ jwC - co R CTT CT . The right hand side of this relation

xl L S ML

differs from the ideal case by containing a small term which is it/ 2 radians out of

phase with jwC . Since the measurement of y is made on a "black box", the results

S

of the measurement could be caused either by the circuit in Fig. 5b or Fig. 5c.

Fig. 5c is the schematic representation of a guarded capacitor with capacitance C

g

2 —1

and dissipation factor equal to -l/rnC R' where R' = (w R C C ) . The dissipation

s H L

factor is negative. In the case of our portable standard capacitor, the negative

dissipation factor was caused by the unsuspected presence of a layer of a high-loss

adhesive between the guard and ground.

Current Comparator Bridge

The real part of the dielectric constant and the dissipation factor of a

sample are measured by balancing the current in the sample capacitor against the

current in the standard capacitor using the current comparator bridge. A simplified

version of how this is done is illustrated in Fig. 6. The lossy sample capacitor is

represented by a parallel combination of an ideal capacitor, C^, and a resistor, R .

At balance (i.e., zero signal at the detector, D) since = IgNg,

C

X

nSD

nDX

C

X

(17)

and
-18-

y B llS(j«C--«2 RCL C H )

*12 V| S

R' = ( w

2 RC L C H )

-I

FIG. 5 NEGATIVE O.F. MODEL
-19-

QO

(0

CD

Li.

SIMPLIFIED

CURRENT

COMPARATOR

BRIDGE
- 20-

DF = (a) R

g

Cg)"

1

(18)

where

(19)

The transformer in Fig. 6 is a three-winding current transformer or a current

comparator. Extensive work on this type of bridge has been done at the National

Unfortunately, the bridge in Fig. 6 is not practical because resistance

standards for high voltages are impractical to make, and another method for balancing

out the in-phase or loss current must be sought.

The circuit in Fig. 7 provides a suitable method for balancing the loss component.

An operational amplifier, which provides a virtual ground for the current through the

/ bs

Ng winding (the amplifier's gain being greater than 10 ), outputs a voltage signal

equal to -V C 0 /C_, typically one thousandth of the source voltage, V, or smaller,

b r A variable resistance which is connected between the amplifier output and the third

current-carrying ratio winding, N» (opposite in polarity to N ) is used to balance

D b

the loss component. The balance equations now become:

so that the bridge can be made direct reading in dissipation factor for a particular

frequency (e.g., 60 Hz).

The resistance of the leads between the voltage source and the capacitors and

between the capacitors and the bridge will contribute to the dissipation factor.

In the case of the standard capacitor side of the bridge, it would take a lead

resistance of about 25 ohms to cause an apparent decrease in DF of 1 x 10 On the

rj Q Research Council in Canada and at NBS. ’

( 20 )

D.F. = (N

3

/N

g

) (1/w C

p

Rg) ( 21 )
- 21-

°o

oo2 <

c6

Ll

CURRENT

COMPARATOR

BRIDGE

USING

ACTIVE

CIRCUITRY

FOP

Q.F.

BALANCE
- 22-

sample capacitor side of the bridge, however, the lead resistance could become

significant. From (2) the capacitance for the sample capacitor could be as large

as 1000 pF so that an increase in DF of 1 x 10 ^ would be caused by a lead

resistance of 2 to 3 ohms. The actual lead resistance in our measuring circuit

is less than 1 ohm so that the lead resistance is still negligible. Future work

on larger capacitance sample holders will require careful consideration of the

effect of the leads. The bridge in Fig. 8 remedies this problem by automatically

compensating for the lead resistance between the sample capacitor and the bridge.

The small voltage, v, caused by this lead resistance results in the voltage drop

across the sample capacitor being V-v instead of V. To compensate for this, the

voltage v is inverted and passed through the capacitor, C ' , the resulting current

b

entering the N winding. The total current in the N winding then becomes

b b

I

g = VjtoCg - vjwCg (22)

or

I

g = jcoCg (V - vCg/Cg) (23)

If Cg is set equal to Cg, then

Ig = jrnCg (V-v) . (2k)

The resulting current is as if a voltage V-v was placed across the standard

capacitor, the same voltage that is across the sample capacitor. The compensating

circuit, therefore, has eliminated the effect of this lead resistance.

From (2), (20), and (2l) the dielectric-constant, s', and the dissipation

factor, D.F.

,

of the sample can be found from the bridge by the following equations:

s' = (1.08 x 10 S (d n

gD

n

DX

C

g

) (25)

D.F. = (N

3

/Ng) (1/co C

F

Rg) + 1.8 x 10 (26)
- 23-

O

<0

FIG.

8

CURRENT

COMPARATOR

BRIDGE
-2kThe effect of the dissipation factor of the standard capacitor discussed in the

previous section is included in ( 26 ).

The estimated uncertainty of (26) is ±1 x 10 ^ at 60 Hz. The uncertainty in (25), i

the dielectric constant, may be as large as ±10 percent even though the turns ratios,

-6

N and N , are known to ±1 x 10 . This is because the actual electrode spacing

at h.2 K is not known. In our measurements the room temperature value of d is used

thereby assuming no thermal contraction of the sample. The thickness of these thin

samples is not always uniform which also contributes to the error. Errors due to

coating the sample with paraffin oil (discussed below) are negligible.

RESULTS

The equipment described previously was used to measure samples of polymer tapes

and epoxies submitted by BNL, ORNL (Oak Ridge National Laboratory), and UCC-Linde. As

far as the polymer tapes were concerned, only those that proved to be among the most

promising from mechanical tests, low-voltage electrical tests, or economic

considerations were sent to us by BNL. Each sample was measured at least twice to test

repeatability and prevent erroneous values caused by the occasional cracking of some

sample materials at cryogenic temperatures. All values reported are at b.2 K and

atmospheric pressure, and all measurements were made with the material actually submerged

in liquid helium. The voltage values reported below are the root-mean-square values

of the applied 60-Hz voltage.

As a consistency check we measured the dissipation factor of liquid helium at k.2 K.

This was accomplished by placing three evenly spaced circular pieces (l mm diameter) of

polycarbonate on the guard ring to separate the active electrode from the high voltage

electrode. The resultant electrode spacing was 75 ym. The liquid helium filled

capacitor was somewhat noisy at elevated electric stress. At 1.5 kV/mm the noise was

absent and a measurement yields a 60 Hz dissipation factor of (+0.3 ± 0.7) x 10

This is consistent with the fact that liquid helium has no intrinsic ' loss mechanisms

at power frequencies.
-25-

The results of measurements on single layers of insulators are shown in

9 Tables I and II. The voltage dependence of the dissipation factor is in most cases

quite small. Measurements were terminated at the first signs of corona onset as

evidenced by noise spikes on the detector output. The repeatability of polymeric

samples from the same manufacturer is generally good although polymers with the same

generic name may differ markedly.

In private conversations with Mopsik of the Polymers Division, NBS, and King

and Thomas of Stanford University we found good agreement in the dissipation factor

data at b.2 K and 60 Hz.

General comments can be made about the different polymer films listed in Table I.

The polyethylenes and polypropylenes (similar in chemical structure) both have

-6 dissipation factors considerably less than 30 x 10 at design stresses of the order

of 20 kV/mm. These films along with the polyamide sample, however, have poor

mechanical properties at liquid helium temperatures. The polycarbonate and

polysulfone films are much better mechanically but have dissipation factors in the

range of 50 to 100 x 10 An attempt by the manufacturer to improve the dissipation

factor of one of these materials (green polysulfone) by reducing the concentration

of sodium impurities was somewhat successful.

While the dissipation factor of most of the materials increases slightly with

increasing voltage, the two polyether-sulfone samples have a negative voltage

coefficient. This is similar to the observed behavior of power-factor correction

capacitors that use oil-impregnated paper insulation. The effect in that case,

according to Garton^, is due to the trapping of the mobile ions before the half-cycle

is completed. Whether a similar mechanism is causing this behavior in polyethersulfone is not known to us. Since several of the polyether-sulfone films cracked

during our measurements, the mechanical properties of this material are evidently poor.

The results of the epoxy measurements are presented in Table II. The epoxies

j had a nonnegligible voltage coefficient so that the dissipation factors listed are
-26-

voo

x

-=r 1—

LTV t— 00 -=T LTV VO 00 LTV OV OJ o

OJ VO • OJ • Ov 1—

O t— VO C—

VO c— rH i—

rH

x

cd

a

cd Eh

a;w

cd P>rHO

>

VO

I O

x

C

Ov Ov CO c— VO LT\ o vo o CVl CO CVJ OJ vo rH OJ • o OJ rH CO OJ X UO i—

rH i—

rH

3

OJ

-cladC

cd

co W

o

VO

+5

cd

to P

G

co

CD ce

fto

>>

Si

CO

M

CD

i—

,0

ai Eh

coco

CDp

-pCO >M

o ad

bo <d

cd *h

-P rH

rH ft O ft >

a

•h

LTV t— o o vo o o o rH Ov Ov o bOJ C\J CVJ OJ rH on 1—

OJ '—

— p* OJ — — '

— — — '

'

— '

'—

COa

ft >

o o o o o o o o o o o o o

o o o o o o o o o o o o o

o o o CO o CM OJ o o OJ o Pi- GO

rH OJ CVJ OJ rH 1—

1—

CO 1—

rH

CO

COo

ft

7\

n <

o

rH 1 ad A .—

-—. . p -—

G d w v cd i—

CD ad ad ad ad cd ID as 0) v <3; PCd pa •H rH -P CD CD CD CD CD ft CD (V *H 1 CD 1 G -p -P -p -P i—

pH P d -P QJ CD

<u c CD G G G C o X bO tiO

* H a c G

-p o < -H CD CD c_> < CD pa cd V - 3 0 <D O

cd rH x 1 p Q -H PQ -H 1 r-^ 1 -H 1 -H 3 Pi -H ft

CD O 1 P J ^ CD ad CD P CD P pa U O W Pc 1—1 p rH S 0) -p CD O CD O C 0) G O G O i 1 J i a G 0 G OJ

' -P cd >> G r-" c CD -P CD CD CD <D as (D -H CO CO d G H <D >> ad CD >» pH G pH C>> rH !>> G G G G 1 1 c <u a) O rH H pH CD i—1 pH >> <D >> H pH O O O O cd P H P <u •d -h X as p6 H -p >> rH ft -H ft pH ft rH ft ft ft ft S3 <U h as •H •h ^ P -H X! a) cd X cd O P O cd o cd H rH pH rH X

§ ° cd tt P *rH G -p -H P O P -H . P *H 3 3 0 pi p p

“ X O CO 1 o cd ID X -H CD X ft 1 ft X CO CO CO CO CD CD 0 as

| >> G t>> -H >>d a >> cd £ G S 3 K cd >. >> >» >> > >> 3 >,

rH O p-H G rH *H 9 pH *<H rH O H -H pH *H pH pH pH rH CD H . H pH O O G o 3 O .o H O X O G O A O X O O O o ft O 0 O

CP CP CP CP CP CP CP

*=• CP CP CP CP cp C. CP
-27-

Table II. Summary of Epoxy Results at 60 Hz and k.2 K

Material'" Tan 6

Epoxy A, 1.6-mm thick 560 x 10

Epoxy B, 2.8-mm thick 3*+0

Epoxy B, U80-ym thick 280

Epoxy C, 360- ym thick 185

Epoxy C, 560-ym thick 210

Epoxy C, 630- pm thick 210
-28-

the extrapolated values for zero voltage. The resulting estimated uncertainties

for these epoxy measurements are ± 5 % of the tabulated value. Sample preparation

(including catalyst concentration) may account for the varying results on identical

materials of differing thicknesses. The apparent increase of the dissipation factor

with sample thickness may be a real effect resulting from the increased probability

of voids or other defects. The maximum dissipation factor acceptable for the spacers

in the UCC-Linde SPTL^ is about 500 x 10

In order to make these measurements, it was necessary to coat the electrodesample interfaces with paraffin oil. Presumably this procedure suppresses corona

at the interfaces. Measurements by King and Thomas and by us have placed an upper

-6

limit of 1 x 10 on the dissipation factor of paraffin oil at 60 Hz. It has been

our experience that when our samples have not been coated with paraffin oil prior to

insertion into the sample capacitor, the measured dissipation factor exhibits a

strong voltage coefficient. Perhaps this, in part, is caused by the presence

of helium bubbles. The corona might be suppressed in supercritical helium.

To examine further the effects of paraffin oil on various interfaces, we studied

several stacking arrangements of 30 ym-thick polypropylene films. The dissipation

factor of this material has a very small voltage coefficient over a wide range of

voltage stress. We measured the dissipation factor of three-sheet stacks of this

material. In one case both sides of each sheet were coated with paraffin oil. In

another instance only the metal-insulator interfaces were coated. We also measured

a two-sheet stack with oil only between the metal-insulator interfaces.

The results are plotted in Fig. 9. The slopes are consistent with measurements

12 made on polyethylene using the calorimetric method but it is clear that the exact

nature of the interfaces plays an important role. Present designs call for the

insulation of a flexible superconducting cable to be impregnated with helium at

temperatures of 7 to 9 K and pressures from 1 to 1.5 MPa (10 to 15 atmospheres).

It is therefore our intention to continue our measurements in an apparatus which will

operate at these conditions.
•

SINGLE

SHEET

OF

POLYPROPYLENE

50X|0~ 6h

COATED

WITH

PARAFFIN

OIL

-29-

o

o 111

111 »-

I- < < o

cr> CO UJ

m

UI

o

ui

a< <• u.

A z u. UI CC UI

UI

-I

ocUI Zui

UI i- z

UI

o

UI >

CL

J>A

1-< O cl

U*O

0C

CL>•

o

a:

a.>

_i

OCO

1-< o a:

a:o

0.

H > < a

9)

ui

o

a.

-13

9) 2 ^

9>

o

OL

o<

u.

OF 1

OF -

IN OF

acUIH

9> -1 CO

Z

1- < H

Ul 1- UI J" Ul

J

UI U' UI “ UI -1 2 X 2 z <

9> CO CO

CM IO ro o +

OO

ro «©£

to

O

CVI ii

V.> OO

0)o

Ll

doiovd Nonvdissia

MULTI-LAYER

EFFECT
-30-

WORK IN PROGRESS: CORONA DETECTION SYSTEM

The results reported to date are the outcome of measurements designed

primarily to determine dissipation factors in single-layer samples at high

electrical stress. The actual design of a flexible AC SPTL calls for wrapped

plastic tape insulation impregnated with fluid helium. In such a system, the

occurrence of corona between tape layers or in butt gaps may dominate other loss

mechanisms. Corona could also prove to be the most important cause of insulation

aging in a regime in which "normal" thermal aging is suppressed.

For these reasons we are preparing to study corona losses in simulated

cable geometry and environment. The corona detection circuitry can be placed as

a shunt across the circuit already in use for dissipation factor measurements

(see Fig. 10). In this way, it will be possible to measure dissipation factor

and corona simultaneously. The coupling impedance, Z, is an LRC circuit which is

driven into oscillation by a partial discharge in the test sample (the other highvoltage circuit components must be discharge free). The amplitude of the first

oscillation is directly proportional to the magnitude of the partial discharge

so long as the characteristic period of the LRC circuit is long compared to the

rise-time of the partial discharge. The voltage appearing across Z can be

calibrated in picocoulombs by use of a pulse generator in accordance with standard

13,

1* practice.

For measurement of corona onset, usual practice requires that the signal across

Z undergo amplification and display on an oscilloscope. Narrow-band amplification

achieves a low noise level at the expense of a correspondingly limited response

time

Our corona detection apparatus will be designed to sort out partial discharge

events as a function of amplitude. These will then be displayed as a histogram of

discharge frequency versus magnitude in complete analogy to the pulse height analysis

experiments of nuclear physics. The area under the histogram is a measure of the
HIGH

VOLTAGE

- 31-

ifDO

z<

H*

^

COO

FIG.

10

COROfMA

DETECTIOIM

CIRCUIT
-32-

loss energy due to partial discharges. The shape of the histogram should provide

an indication as to the source of the discharges .

Aging of the dielectric can he

discerned by observing the evolution of histogram features.

Pulse-height analysis in our laboratory will be accomplished using a minicomputer

interfaced to an oscilloscope. Partial discharge events will be detected using the

circuit shown in Fig. 10. The magnitude of each event will be converted to a binary

number which is then stored and manipulated by the minicomputer. The intervening

circuitry between the voltage across Z in Fig. 10 and the A/D converter has been

designed and will now be described.

Electronics

The detection impedance, Z, is an LRC circuit whose characteristic response to

an impulse is a critically damped wave whose width is ^3 ps. The rest of the circuitry

is shown in Fig. 11. Since the response of the LRC circuit may be of either polarity

(depending on the polarity of the partial discharge) the first step is to rectify

the output using a diode bridge network. It is recognized that the non-ideality

of real diodes will make the output of the bridge somewhat non-linear with voltage

but this is not seen as a serious problem.

Next the signal is stepped up by a high-frequency transformer. This transformer

accomplishes several things. First, it isolates the output of the diode bridge from

ground. Second, it blocks the 60 Hz carrier signal from the rest of the circuitry.

Third, it can be used to step up the signal voltage to a level at which the signal

noise is equal to the inherent band-width noise of the succeeding amplifier stage.

This voltage transformation will then allow the maximum signal -to-noise ratio to be

achieved.

The signal is then amplified by a device with adjustable bandwidth. The bandwidth

j, selected is determined by the various constraints of ability to resolve rapidly

occurring events, bandwidth noise, and signal shape. The signal must have a shape

which is suitable for the peak-and-hold circuit which follows the amplifier.
- 33-

Ul

m

o

tr

H

CO

FIG.

II

SIGNAL

PROCESSING
Fig. 12 shows a schematic drawing of the peak-and-hold circuit we have chosen.

When a pulse which has been amplified and shaped appears at the input of A its peak

value will be held at the output of A^. The speed of the peak and hold circuit is

determined by the value of the 500 pF capacitor and the current available from A-^

d V

out

dt I/C .

In our circuit, C = 500 pF and I = 100 mA so that the slowest peak acquisition time

is 500 ns. The droop rate (i.e., rate at which the peak voltage decays) is equal

to the leakage current divided by the capacitance. Amplifier A^ has an FET input to

keep leakage current below 100 pA. This value then gives a maximum droop rate of

0.2 V/s. This rate is sufficiently slow for data to be transferred to the A/D

converter with negligible error.

The comparator in Fig. 12 signals the A/D converter to ignore any signal below

When the comparator receives a signal, V , , which exceeds V it sends a

delayed signal to the A/D converter to read V . The delay is necessary in order

OUT.

to give adequate time for the data pulse to reach its peak. The switch is opened

and is closed during the time the A/D converter is working.

When conversion is finished, discharges the capacitor, opens, closes

and the circuitry is ready to receive another pulse.

Data Analysis

The high-speed A/D converter (conversion time of h ys) will respond to each

corona event by sending 12 parallel bits of information to the computer for processing.

By using a selector channel input (direct memory access) the data enters the memory

without central processor involvement. This maximizes the rate that data can be

entered and allows the minicomputer to be doing other chores.

In order to minimize the dead-time, a two buffer scheme will be used to process

the data. While buffer A is being filled with data from the A/D, the contents of

buffer B are being sorted according to amplitude and then outputted on an oscilloscope
100 k

- 35-

FIG.

12

PEAK

-AND-HOLD

CIRCUIT
-36-

display. After A is filled, the contents of A are sorted and new data enters B.

After an experiment is completed, a record of the final display will he dumped

onto a floppy disc. Each disc contains about 60 tracks usable for data storage.

A track contains 32,768 bits—enough storage for one complete experiment. With the

use of the floppy discs, different experimental runs can be compared, averaged or

otherwise manipulated by the minicomputer.

Progress

The individual circuits described in the Electronics section have been

breadboarded and tested. The operation of the entire circuit, however, has not

yet been attempted. The A/D converter has been interfaced to the minicomputer.

Programs (in Assembly Language) need to be written to sort the data and output it

to the oscilloscope display.

CONCLUSION

The dissipation factors of insulating materials being considered for AC SPTL's

have been measured at high electric stress. During the course of this work

considerable effort was made to insure accuracy of dissipation factor measurements

to ±1 x 10 A current comparator bridge designed at NBS easily provided the needed

precision. The required accuracy was achieved by performing a careful determination

of the dissipation factor of a compressed-gas standard capacitor. The standard then

was balanced against unknown sample dielectrics using the current comparator bridge.

As a check of the experimental system, the dissipation factor of liquid helium was

measured and found to be less than 1 x 10 ^ in agreement with theory.

Technical papers describing the experimental technique and the results obtained

have been presented at two dielectrics conferences.

Measurements of stacked layers of plastic —in simulation of the insulation

of a flexible cable—suggest that interfacial losses cannot be ignored and, in fact,

may predominate. Future efforts will therefore aim at measuring the dissipation
- 37 -

factor of layers of plastic in a more faithful simulation of cable geometry and

environment. Partial discharges occurring in the samples will be studied using

pulse-height analysis techniques.
References

1. E. B. Forsyth, G. A. Mulligan, J. W. Beck and J. A. Williams, IEEE PAS -9^ , l6l (1975).

2. G. Bogner and P. Penczynski, Cryogenics, l6_, 355 (1976).

3. 1973 Progress Report, part I, BNL Power Transmission Project, p. 87.

U. F. I. Mopsik, 197*+ Annual Report, Conf. on Electrical Insulation and Dielectric

Phenomena, to he published.

5. C. N. King and R. A. Thomas, 197^ Annual Report, Conf. on Electrical Insulation

and Dielectric Phenomena, to be published

6. A. V. Astin, Journal of Research NBS , 22, 673 (1939).

7. N. L. Kusters and 0. Petersons, IEEE CE-82 , 606 (1963)

8. 0. Petersons and W. E. Anderson, IEEE IM-2U , 336 (1975).

9. Certain commercial materials are identified in order to adequately specify the

experimental results. In no case does such identification imply recommendation

by the National Bureau of Standards, nor does it imply the material is the best

available.

10. C. G. Garton, Proc. IEE 88 II, 103 (19^1).

11. Sept. 2, 1975-March 31, 1976 Progress Report, Union Carbide Corporation-Linde

Division, p. 9-

12. Semiannual Progress Report for NSF RANN Grant No. GI-3715» p. 10, Oct. 197^.

13. ASTM D-1868-68, 1969 Book of ASTM Standards , part 29, 88U.

ik. F. H. Kreuger, Discharge Detection in High Voltage Equipment , Elsevier, N.Y.,

(1965).

15. R. Bartnikas, IEEE IM-22 , U03 (1973).
- 39-

Al. Bibliography

The following list of references includes articles which we have found

particularly useful. There are four kinds of information represented:

general papers on design considerations for superconducting transmission

lines, papers dealing specifically with dielectric loss or breakdown at

cryogenic temperatures, papers which bear on methods for precise measurement of dissipation factor, and papers describing corona detection systems.

To this list must be added the progress reports of other ERDA- supported

ac superconducting transmission line research, specifically those of

Brookhaven National Laboratory, Stanford University, Oak Ridge National

Laboratory and Union Carbide Linde Division.

Allan, R. N. and Kuffel, E. , "Dielectric losses in solids at cryogenic

temperatures", Proc . IEE 113 , *+32 (1968).

Astin, A. V. , "Nature of energy losses in air capacitors at low frequencies".

Journal of Research NBS 22_, 673 (1939) •

ASTM D-150-68, "Standard methods of test for ac loss characteristics and

dielectric constant (permittivity) of solid electrical insulating

materials", 1969 Book of ASTM Standards , part 29, 66.

ASTM D-1371-68, "Recommended practice for cleaning specimens for insulation

resistance, surface resistance, and volume resistivity testing", ibid., 666.

ASTM D-1868-68, "Detection and measurement of corona pulses in evaluation

of insulating systems", ibid., 884.

Bartnikas, R. , "Effect of pulse rise time on the response of corona detectors",

IEEE EI-7 , 3 (1972).

Bartnikas, R. , "Use of a multichannel analyzer for corona pulse-height distribution

measurements on cables and other electrical apparatus", IEEE IM-22 , 4-03 (1973).

Baylis, J. A., et al., "AC losses in a composite tubular superconductor for

power transmission", Cryogenics l4_, 553 (1974).

Belanger, B. C., "Superconducting power transmission programme in the U.S.A."

Cryogenics 15, 88 (1975).

Belanger, B. C., "Dielectric problems in the development of resistive cryogenic

and superconducting cables", 1973 Annual Report Conf. on Electrical Insulation

and Dielectric Phenomena, 486 (1974).

Bobo, J. , et al. , "Dielectric strength of polymers at cryogenic temperatures

under vacuum", Vacuum l8_, 397 (1968).

Bogner, G. , "Transmission of electrical energy by superconducting cables", NATO

Advanced Study Institute, Entreves, Italy, 1973, Superconducting Machines and

Devices

,

S. Foner and B. B. Schwartz, eds, Plenum, 4 01 (1974).
-UOBogner, G. , "Cryopower transmission studies in Europe", Cryogenics 1_5_, 79 (1975).

Bosack, D. J. , "Development of the dielectric system for a helium cooled

superconducting transmission line", 197*+ Annual Report Conf. on Electrical

Insulation and Dielectric Phenomena, 59*+ (1975).

Burnier, P. and Moreau, J. , "Etude des dielectriques aux temperatures

de l'hydrog^ne liquide". Rev. Gen. l'Elec. 77 7 600 (1968).

Carson, R.A.J., "Low-temperature dielectric relaxation in polyethylene", Proc

Roy. Soc. Lond. A 332, 255 (1973).

Chant, M. J. , "Dielectric properties of some insulating materials over the

temperature range k. 2-300 °K" , Cryogenics 7_, 351 (1967).

Dubois, P. , et al., "Research and development of superconducting cables for

high power transmission", Proc. 1972 Applied Superconductivity Conf., IEEE

Pub. No. 72CH0682-5-TABSC , 173 (1972).

Fallou, B. and Bobo, M. , "Electrical properties of insulating materials at

cryogenic temperatures", 1973 Annual Report Conf. on Electrical Insulation

and Dielectric Phenomena, 51*+ (197*+).

Fallou, B. and Galand, J., "Proprietes de 1' helium liquide". Rev. Gen. l'Elec.,

77, 59*+ (1968).

Gallagher, T. J., "Mobility, conduction and breakdown in cryogenic liquids:

a review", 1973 Annual Report Conf. on Electrical Insulation and Dielectric

Phenomena, 503 (197*+).

Garton, C. G. , "Dielectric loss in thin films of insulating liquids", Proc.

'IEE 88 II, 103 (19*+1)

Gauster, ¥. F., et al., "Dielectrics for superconducting systems", 1973 Annual

Report Conf. on Electrical Insulation and Dielectric Phenomena, 53*+ (197*+).

Gerhold, J. , "Dielectric breakdown of helium at low temperature". Cryogenics 12 , 370 (1972).

Goldschvartz, J. M. and Blaisse, B. S., "Electrical breakdown of liquid helium",

Brit. J. Appl. Phys. 17, 1083 (1966).

Horigome, T., "The present state of R&D for superconducting transmission in Japan",

Cryogenics 15_, 91 (1975).

Iwata, Z. and Kikuchi, K. , "Electrical insulation for liquid nitrogen cooled

EHV cryogenic cable", 1973 Annual Report Conf. on Electrical Insulation and

Dielectric Phenomena, 49*+ (1974).

Jefferies, M. J. and Mathes, K. N., "Insulation systems for cryogenic cable",

IEEE PAS-89 , 2006 (1970).

Jefferies, M. J. and Mathes, K. N. , "Dielectric loss and voltage breakdown in

liquid nitrogen and hydrogen" , IEEE EI-5 , 83 (1970).
- 1* 1-

Kreuger, F. H. , Discharge Detection in High Voltage Equipment , Elsevier, N.Y.

,

(1965).

Kusters, N. L. and Petersons, 0., "A transformer-ratio-arm bridge for highvoltage capacitance measurements", IEEE CE-82 , 606 ( 1963 ).

Lampard, D. G. , "A new theorem in electrostatics with applications to calculable

standards of capacitance", IRE Institution Monograph Wo. 2l6M, 271 (1957).

Long, H. M. and Notaro, J., "Design features of ac superconducting cables",

J. Appl. Phys., **2, 155 (1971).

Mathes, K. N. , "Dielectric properties of cryogenic liquids", IEEE EI-2 , 2h ( 1967 ).

Mathes, K. N. and McGowan, E. J. , "Problems with dielectric measurements at

cryogenic temperatures". Measurement of Dielectric Properties Under Space

Conditions , ASTM STP 1*20, 3 ( 1967 ).

Meats, R. J., "Pressurized-helium breakdown at very low temperatures", Proc . IEE,

119 , 760 (1972).

Meyerhoff, R. W. , "AC superconducting power transmission", Proc. 1972 Applied

Superconductivity Conf . , IEEE Pub. No. 72CH0682-5-TABSC , 19U (1972).

Muller, A. C., "Insulating tape characteristics at cryogenic temperatures",

1973 Annual Report Conf. on Electrical Insulation and Dielectric Phenomena,

52l* (197*0.

Nelson, R. L. , "Dielectric loss of liquid helium". Cryogenics 1** , 3*4-5 (197*0*

Nelson, R. L. , "Bridge measurement of very low dielectric loss at low

temperatures", Proc. IEE 121 , 76** (197*0.

Petersons, 0. and Anderson, W. E., "A wide-range high-voltage capacitance bridge

with one ppm accuracy", IEEE IM-2** , 336 (1975).

Phillips, W. A., "Low temperature dielectric relaxation in polyethylene and

related hydrocarbon polymers", Proc. Roy. Soc. Lond. A 319 , 565 (1970).

Rigby, S. J. and Weedy, B. M. , "The effects of semiconducting screens on the

dielectric loss of liquid nitrogen impregnated taped cable insulation"

,

Cryogenics 15., 1*65 (1975).

Rigby, S. J. and Weedy, B. M. , "Partial discharges in liquid-nitrogen impregnated,

taped-cable insulation", Proc. IEE 123 , 165 (1976).

Shields, J. Q. , "Phase-angle characteristics of cross capacitors", IEEE IM-21,

365 (1972).

So, E. , "Losses in electrode surface films in gas dielectric capacitors",

thesis, 1973, unpublished.

Swan, D. W. and Lewis, T. J. , "Influence of electrode surface conditions on the

electrical strength of liquified gases", J. of the Electrochem. Soc. 107., 180 (i 960 ).
-k2-

Swift, D. A., "Dielectric design criteria for solid-insulated superconducting

ac cables", Proc . IEE ll8, 1237 (1971).

Swift, D. A., "Dielectric design for a superconducting ac cable with solid

insulation". Rev. Gen. l'Elec. 8U_, 7^1 (1975).

Thomas, R. A. and King, C. IT. , "Low-temperature dielectric loss in polyethylene",

Appl. Phys. Lett. 26_, 4o6 (1975).

Thompson, A. M. and Lampard, D. G. , "A new theorem in electrostatics and its

application to calculable standards of capacitance". Nature 177, 888 (1956).

Vincett, P. S. , "Calorimetric measurement of very low dielectric loss at low

temperatures", Brit. J. Appl. Phys. 2_, 699 ( 1969 ) •
43 -

PART II

INVESTIGATION IN THE POLYMERS DIVISION ON THE DIELECTRIC PROPERTIES

AND THE

STRUCTURE OF POLYMER TAPES FOR USE AS INSULATION IN SUPERCONDUCTING CABLES

Report Covering Period November 1974 to June 1976 (NBSIR 76-954)

by

F. I. Mopsik and S. J. Kryder (Bulk Properties Section)

and

F. Khoury, J. P. Colson and L. H. Bolz (Structure and Properties Section)
TABLE OF CONTENTS

ABSTRACT p. 45

SUMMARY p. 46

1. Dielectric Measurements (F. I. Mopsik and S. J. Kryder) p. 51

1.1 Introduction p. 51

1.2 Apparatus and Procedure p. 52

1.2.1 Cell p. 52

1.2.2 Measurement Procedure p. 56

1.2.3 Measurement Accuracy p. 57

1.3 Results p. 59

1.3.1 Polycarbonate p. 59

1.3.2 Nylon 11 p. 61

1.3.3 Polysulfone p . 61

1.3.4 Polyethylene p. 63

1.3.5 Polypropylene p . 68

1.4 Discussion p. 70

1.5 Summary p. 72

2. Aspects of the Fine Structures of Polymer Tapes

J. P. Colson, and L. H. Bolz)

(F. Khoury, p. 73

2.1 Introduction p. 73

2.2 Crystalline Orientation and Order in the Tapes p . 75

2.2.1 Background and Experimental p. 75

2.2.2 Polypropylene p. 77

2.2.3 Nylon 11 p. 93

2.2.4 Polycarbonate p . 96

2.2.5 Polyethylene p. 102

2.2.6 Discussion and Summary p. 108

2.3 Some Observations on the Surface Textures of Polymer Tapes p. 110

2.3.1 Polypropy lene-A Tape p. Ill

2.3.2 Polycarbonate-A Tape p. 113

2.3.3 Polyethy lene-A Tape p. 115

2.3.4 Summary and Comment p. 115

REFERENCES p. 117

TABLES p. 120

GLOSSARY p. 127
45 -

ABSTRACT

This report is divided into two sections. The first section is on the

dielectric properties of the polymer tapes which are being evaluated as insulation for the Brookhaven AC Superconducting Power Transmission Cable Project. In

order to measure dielectric loss levels in the tapes a special test cell has been

assembled that measures six polymer tape samples at temperatures from 4 K to 300 K.

_ £ The loss resolution in tan 6 is 1 x 10 . Samples of polyethylene, polypropylene,

polycarbonate, Nylon 11 and polysulfone have been studied from 4 K to 273 K. Poly-

_ 5 ethylene, Polypropylene and Nylon 11 all exhibit a value of tan 6 of 20 x 10 or

less at temperatures of 6-8 K and 100 Hz and meet the required dielectric criteria

for use in the cables. The presence of antioxidant in polyethylene samples increases tan 6 below 30 K. The second section of the report is on aspects of the

structures of the polymer tapes. In particular, the crystalline orientation in

polyethyelene , polypropylene, Nylon 11 and polycarbonate tapes have been surveyed

using wide angle x-ray diffraction as the main probe. The results are briefly

discussed with reference to the mechanical and dielectric properties of the tapes.

Some initial observations illustrating differences in surface texture between

opposite surfaces in some tapes are also presented.
SUMMARY

This report on the evaluation of polymer tape insulation for the AC superconducting power transmission cable project at Brookhaven National Laboratory

(BNL) is divided into two main sections. Measurements on the dielectric properties

of polymer tapes are reported in the first section. Observations on the crystalline

orientation and the topography of the surfaces of some tapes are presented in the

second section.

1. Dielectric Properties

In order to determine the dielectric properties of the polymer tapes, a special

test cell has been assembled. The cell can measure the dielectric constant and loss

of six samples at the same time at any temperature in the range 4.2 K to room temperature at audio frequencies. The bridge used with the cell allowed a loss resolution

—6

in tan 6 of 1 x 10 . The materials studied were submitted by BNL and included

samples of tapes made from the following polymers: Polycarbonate (4.

f -dioxydiphenyl2.2'-propane carbonate), polysulfone, Nylon 11, polyethylene and polypropylene.

Most samples were measured over the entire temperature range 4.2 K to room temperature

at frequencies of 100 Hz and 1 kH. The 100 Hz data are sufficiently representative

of the expected behavior at 60 Hz.

The Polycarbonate-A, Poly carbonate-B, and Polysulfone-A tapes exhibited excessive loss at 6-8 K compared to the desired level of tan 6 = 30 x 10 ^ for use in the

— 6

power cable. These tapes had a tan 6 in excess of 80 x 10 . The Nylon 11-A sample

— 6 had a tan 6 of 20 x 10 at 6-8 K but poor mechanical properties has ruled out the

use of this tape in cables.
47 -

Most of the loss measurements were carried out on polyethylene and polypropylene, which are the main candidates for use in the power cables. Except

for a series of polyethylene samples specially prepared for BNL which contained

varying amounts of antioxidant and which are discussed separately below, all the

polyethylene and polypropylene tapes met the criterion for dielectric loss at

6-8 K. There were some significant differences among these tapes, however.

Except for one of the polypropylene tapes (Polypropy lene-D) all the polypropylene

and polyethylene tapes showed the presence of a loss peak below 4 K. Furthermore,

with the exception of three polypropylenes (Polypropylene A, B and D) tan 6 was

10 x 10 ^ or less at 4-10 K. The loss peak below 4 K was strong enough in the

— 6 Polypropy lene- A and Polypropy lene-B tapes to raise tan 6 at 4 K to 30 x 10

Polypropy lene-D showed a very broad loss peak at 30 K that caused tan 6 to remain

at 20 to 30 x 10 ^ over the entire 4-10 K range.

Measurements on a series of polyethylene samples in the form of sheets specially

prepared for BNL from polymer to which different amounts of antioxidant were added,

showed that the presence of antioxidant in polyethylene can give rise to a loss

peak below 4 K. The loss increased with the amount of antioxidant added to the

polyethylene and could be reduced by solvent extraction. The similarity in the

dielectric behavior exhibited by the polypropylene and polyethylene tapes indicate

that, excess loss observed in the former as the temperature approaches 4 K is also

due to the presence of antioxidant. The only exception seems to be the Polypropylene-D sample where a different but unknown mechanism seems present. It could not

be determined however, whether the additional loss due to antioxidant is related

only to its concentration in this tape or whether other factors affect the loss.
48 -

In general the dielectric measurements reported here show that both polyethylene and polypropylene should meet the criteria for dielectric loss at 6-8 K.

The possibility exists, however, that as these materials are modified in order to

enhance their mechanical properties, the changes in the polymer fine structure

could give rise to enhanced dielectric loss either from interactions with any

antioxidant present or the appearance of new loss peaks such as the 30 K loss

peak in the Polyp ropy lene-D sample.

2. Aspects of the Fine Structure of the Polymer Tapes

In addition to their dielectric properties, an important aspect of the selection of polymer tapes for use as insulation in the superconducting cables is their

mechanical properties both at cryogenic temperatures 6-8 K as well as at room temperature. A vital criterion is the ability of the tapes to withstand the tensions

they are subjected to during the tape winding process in cable manufacture. The

current guideline used by BNL in this connection is that the tensile modulus of

the tapes in the direction of their long axis should be 5 x 10^ - 6 x 10^ psi

(3. 4-4.1 GPa) or greater, at room temperature.

The mechanical properties of polymer films are sensitively dependent on the

structure of the films which can vary widely with respect to the overall crystallinity of the film, the orientation of the crystallites in the film, the manifestation

of chain-folding in the crystallites and the occurence of tie molecules between

neighboring crystallites. These various features are governed by the conditions

under which the polymer crystallizes and the extent to which it is subjected, as

is usual in film manufacture, to orientation inducing processes such as uniaxial

or biaxial stretching or rolling. In view of the dependance of the mechanical

properties of tapes on their fine structures and also because of the possible
49 -

influence of structure on dielectric loss at cryogenic temperatures (6-8 K) , a

screening of the respective fine structures of the different tapes was considered

desirable as a first step towards establishing guidelines on how their structures

could be modified or controlled at the manufacturing stage so as to optimize their

mechanical and dielectric properties. A qualitative determination of the nature

of the preferred orientation (s ) of the crystallites in the tapes was therefore

undertaken using x-ray diffraction methods.

Among the features necessary for achieving a high tensile modulus in the

direction of the long axis of the tapes are a high crystallinity, and a highly

preferred orientation of the crystallites with their constituent chains preferentially parallel to the long axis of the tape. The main observation which emerged

in this connection from the x-ray diffraction study of the tapes was that, with the

exception of the Poly carbonate-A, all the other tapes (i.e. the Polycarbonate-B , the

Polypropy lene-A, B, C, D, E, the Polyethylene-A, D, and the Nylon 11- A) fell short

with respect to either crystallinity, or crystallite orientation, or both. It is

correspondingly interesting to note from the measurements of the tensile modulus of

the tapes at room temperature carried out at BNL, that the present criterion for

the tensile modulus was approached closely only by the Polycarbonate-A tape in

which there is a distinct preferred orientation of the crystallites with the chain

molecules parallel to the long axis of the tape. This tape does not, however, meet

the present criterion for dielectric loss at 6-8 K, in contrast with the polypropylene, polyethylene, and Nylon 11 tapes which were satisfactory in this respect but

are mechanically unsuitable. It may be concluded that new tapes made from polyethylene, polypropylene, and Nylon 11 which have been subjected to high enough
50 -

stretching in the long axis direction during manufacture to impart judiciously

high degrees of crystallite orientation with the chain molecules parallel to the

long axis of the tape would most probably satisfy the current dielectric and

mechanical property criteria for use in the cables. The effects of increased

orientation and/or crystallinity on the dielectric properties of such tapes at

6-8 K would have to be checked, however.

It is not clear at this stage whether differences in dielectric loss levels

which were observed among the polypropylene tapes and among the polyethylene tapes

examined in the present study are due solely to differences in additive content, or

whether structural variations between the tapes were a contributing factor.

In addition to the examinations of crystallite orientation in the polymer tapes,

a study of another aspect of the structure of the tapes has been initiated, namely

the nature of their surface textures. This latter aspect is being investigated in

order to obtain insights into the nature of the interfacial contacts between successive windings of the tape in the superconducting cables. The nature of the

contacts between successive layers of tape is of interest to BNL in connection with

the desired flexibility of the cables, as well as the radial thermal conductivity

through the several layers of polymer tape in the cables. Some preliminary light

optical and scanning electron microscopical results on three tapes are reported.

In particular differences in texture between opposite surfaces of the Polypropylene-A, Polycarbonate-A, and the Polyethylene-A tapes are described.
51 -

1. Dielectric Measurements (F. I. Mopslk and S. J. Kryder)

1.1 Introduction

The aims of the Polymers Division in establishing a facility for the measurement of dielectric constant and loss at temperatures as low as 4 K were several.

The most important was to determine the dielectric constant and loss at cryogenic

temperatures of polymer films that were actively being considered as suitable insulating materials for the Brookhaven Superconducting Cable Project. Another was

to provide a facility for testing new materials of possible interest as cryogenic

insulation as they become available. Still another was to have enough measurement

capability to provide background information on possible sources of dielectric loss.

The electrical requirements for polymer insulating tapes used in superconducting

power cables are quite restrictive. They are a dielectric constant, e, less than

2.5 and a dissipation factor, tan 6, less than 30 x 10 at the operating temperatures

of the cable, 6-8 K. These requirements in turn present a difficult measurement

problem. This is both because of the very low loss levels that have to be determined

as well as the form of the samples, films 25-100 ym thick. However, past experience

in the Bulk Properties Section, Polymers Division, enabled the design of a suitable

sample cell that successfully carried out this measurement task.

These considerations and the emphasis on material properties has led to a facility

that allows for the measurement of six samples at the same time for both dielectric

constant and loss. The measurements can be made at frequencies in the audio frequency

range. The temperature can be maintained conveniently at any temperature from 4.2 K

to room temperature. No attempt was made to work at high applied potentials. This

is in contrast to the approach of the Electricity Division where the need for studying

the effects of high applied voltage has allowed the measurement of tan 6 for one

sample at a time of single samples at 60 Hz and 4.2 K only.
- 52 -

1. 2 Apparatus and Procedure

1.2.1 Cell

The main problem in establishing the ability to carry out the necessary dielectric measurements was the design and construction of a suitable sample holder.

The sample holder, or cell, had to be capable of determining very low losses in

thin samples at controllable temperatures. Because of the exploratory nature of

the measurements it was felt desirable, in particular, that the cell could be

used at any temperature between 4 K and room temperature. In addition, to minimize sample handling problems, another desirable feature was the ability to measure

more than one sample at a time. The design that was adopted is shown in Figures 1

and 2. The construction of all the necessary parts and the mechanical assembly was

done for us by Brookhaven National Laboratory.

The basic design consisted of six three-terminal electrode sets put together

as a single unit that is surrounded by two sealed cans. The inner can acts as an

isothermal shield and the outer can provides the necessary isolation from the cryogenic liquid in which it is immersed. As a result, six samples could be measured

during the same run at any temperature from 4 K to room temperature with the temperature held constant to about 0.002 K.

The electrode assembly is shown schematically in Figure 1. Six electrodes

1.5 cm in diameter were circularly arranged in the bottom block that acted as the

grounded guard. The electrodes were held in place by epoxy cement and beryllium

oxide washers for both good electrical isolation and good thermal contact. Six

separate leads were brought out to provide the means to switch from sample to sample.
53 -

THERMOMETER

Figure 1: Schematic diagram of the electrode assembly for the cryogenic dielectric

cell. The hatched areas represent insulating spacers.
- 54 -

(/)

Figure

2:

Schematic

diagram

of

the

entire

cryogenic

dielectric

cell

as

it

is

assembled.

The

rings

projecting

from

the

top

of

the

inner

can

are

used

for

thermal

tempering

of

all

leads

going

to

the

electrode

assembly.
55 -

After the electrodes were mounted, the entire assembly was ground and laped flat

and gold plated. The matching six upper electrodes, 2 cm in diameter, were individually ground, lapped flat and gold plated. They were attached to bellow

assemblies also by epoxy cement and beryllium oxide washers. To minimize thermal

conduction paths, the upper electrodes shared a common lead. The bellows were

connected to a small (0.3 cm dia.) stainless steel tube that was the only mechanical

tie between the upper block and the top of the inner can from which is was suspended.

Apart from electrical leads, the only other contacts to the inner can from the electrode assembly were four loose fitting stainless steel tubes to limit the strain

placed on the connecting tube.

Mounted on the upper electrode assembly were an auxiliary heater, a miniature

platinum resistance thermometer and a germanium resistance thermometer. All leads

going to the electrode assembly were wrapped one turn around tempering rings that

were provided on the top lid of the inner can. This was true for the electrode leads

as well as the others with care being taken to ensure complete shielding of the lead

from the upper electrodes, from the leads of the bottom electrodes.

The entire assembly is shown in Figure 2. The cell and two cans were suspended

by two thin-walled stainless steel tubes from the lid of a Dewar that had a 15 cm

inner diameter. The tubes carried the leads from the cell and also served to connect

the cans to a gas mainfold and diffusion pump. The tubes were 0.9 m long and had

several baffles attached along their length to minimize convective heat losses in

the Dewar. Uniformly wrapped around the inner can, including the top, was a heater

proportioned to maintain a constant heating rate on all surfaces. This heater was

used as the main heater for controlling temperature of the cell.
56 -

All the leads were brought out on the top of the assembly by vacuum feedthroughs to appropriate connectors. The bottom electrodes were connected to

separate coaxial connectors as was the common upper electrode lead. In use, the

electrode leads that were not being used for measurement were covered by shorting

caps to eliminate the effects of interlead capacitance. All the leads were 30

gauge enamel covered wire to minimize thermal conduction except for the electrode

leads which were 26 gauge Teflon insulated wire. This heavier gauge wire was used

to keep effective lead losses low compared to measurement resolution.

1.2.2 Measurement Procedure

Measurements were made by placing six samples 2 cm in diameter in the cell and

sealing the cans in place with indium wire. Both cans were evacuated and back

filled with helium gas at a pressure of 200 mm Hg at room temperature. When the

desired minimum temperature was achieved, the outer can was evacuated and the

temperature was controlled. Temperature was monitored above 20 K by the platinum

thermometer and below 20 K by the germanium thermometer, both of which were calibrated to better than 0.01 K. Both thermometers were supplied a constant current

known to 0.001% and the voltage across them was used both for temperature measurement and control. The current level used in both thermometers gave a sensitivity

of about 400 yV/K. A three mode proportional controller having a resolution of

1 yV and supplying 20 W of DC power to the inner can heater was able to keep the

temperature constant to within 0.002 K. During the electrical measurements, a

pressure of 0.2 MPa (2 atm.) of helium was maintained in the bellows to ensure

adequate electrode contact.
57 -

The bridge used to determine capacitance .and loss was a three- terminal

transformer bridge that used substitution. It had a resolution in terms of

tan 6 of 1 x 10 ^ or better, depending on the sample capacitance. By means of

a standard capacitor calibrated for loss by the Electricity Division, the loss

— 6

uncertainty of the bridge was shown to be 0.5 x 10 expressed as tan 6. Typical

working voltages were 20-40 V.

The useable frequency range of the bridge with the interchangeable transformers that were available was 30 Hz to 10 kHz but sensitivity and balancing time

considerations made a lower frequency of 100 Hz preferable and lead losses made an

upper frequency of several kHz desirable. In the measurements reported here, only

frequencies of 100 Hz and 1 kHz were used. With the frequency range available,

additional frequencies would not have added much additional information and would

have lengthened the measurement time excessively. While no data were taken at 60 Hz,

since tan <5 is a slowly varying quantity with respect to the logarithm of frequency,

the 100 Hz data can be used as 60 Hz data with little extra uncertainty.

1.2.3 Measurement Accuracy

The accuracy of e and tan 6 for the samples measured and reported here was

limited by the samples themselves. The temperature was determined well enough to

be considered exact. The bellows pressure chosen was found experimentally to be

high enough to get as good electrode contact as possible. Higher pressures were

not found to change the results significantly with respect to sample errors. The

only requirement on temperature was that it was constant to keep the cell capacitance constant to facilitate bridge balance. Similarly, the bellows system had to

be completely tight. At one time a small leak developed in the pressure line that

disturbed con ditons enough to make measurements difficult.
58 -

Errors associated with the determination of electrode area and the bridge

accuracy were negligible. The electrode area, needed to determine e, was measured

with the use of gauge blocks and a reference plane to an accuracy of 0.1%. The

bridge had an accuracy of better than 1 ppm. The only problem encountered was

that sometimes the leads vibrated excessively, leading to increased noise at 100

Hz, which deteriorated resolution, although usually not seriously.

The samples themselves were the main limit in the determination of e and

tan 6. One limitation was the determination of sample thickness which enters

directly in the computation of e. Sample thicknesses were measured by micrometer

at room temperature to 1 ym which is an error of 1 to 5% depending on sample thickness. It was this thickness value that was used for all temperatures with no correction made for thermal contraction since this data was not generally available to

us. The rise in e for a material such as polyethylene with decreasing temperature,

as reported later, is undoubtedly partly due to this neglect.

When thermal expansion data do become available, the values of e should be

corrected. Another source of error is the error that results from the films not

being perfectly flat and in perfect contact with the electrodes. This source of

error was checked by the use of Teflon FEP films of varying thickness and known

dielectric constant. The apparent dielectric constant for these films was 3% low

for 125 ym films and 12% low for 25 ym films. These values include the error from

using the micrometer and should be considered indicative only since they are dependent

on the condition of the film surface. Accordingly, these corrections were not applied

to the data. Finally, corrections for the guard gap were not made as they are less

than the other uncertainties in the measurements.
59 -

Sample conditions could also occassionally cause problems. Sometimes a

sample would warp or include a piece of dust, resulting in an unusually low value

of measured capacitance and often enhanced loss, especially at 100 Hz. In most

cases duplicate samples prevented this from being much of a problem and those cases

where it was will be indicated.

1. 3 Results

All the samples described in this report were supplied by Brookhaven National

Laboratory. They were used as received after being cut into 2 cm diameter discs.

Dust was excluded as much as possible.

1.3.1 Polycarb onate

Two different types of polycarbonate film were measured, Poly carbonate-A and

Polycarb onate-B. Both films were about 60 ym thick and both were dyed. Polycarbonate-A was yellow-green and the Polycarbonate-B was yellow-brown. Two samples

were measured for both films with good agreement between the samples. The data

are presented in both Table I and Figure 3.

Both films are characterized by a broad loss peak at about 180 K at 100 Hz.

The peak is broad also in a frequency sense as can be seen by comparing the 100 Hz

and 1 kHz data. While the loss peak for the Polycarbonate-A film is lower than

that of the Polycarbonate-B film, at 30 K and below both films were identical in

terms of loss

In Figure 3, an inset shows the loss behavior of both films in the cryogenic

cable temperature range of 4-10 K. The loss decreases slowly with decreasing

temperature with no indication of any loss peaks. Tan 6 changes from 80 x 10

^

“ 6

at 10 K to 60 x 10 at 4 K. Compared to the maximum loss criterion for use in
4000

60

PQ

9 0000l X 8 UD| 000

o 00- CD C\J

90lx 8 udj

Figure

3.

Tan

6

vs.

temperature

at

100

Hz.

The

circles

are

for

Polycarbonate-A,

the

squares

for

PolycarbonateThe

inset

showing

more

detailed

data

below

10K

is

for

both

polymers.
61 -

a power cable of 30 x 10 ^

, both films are definitely not satisfactory. Furthermore, since the B film has poor crystallinity while the A film is distinctly crystalline and exhibits a high degree of crystalline orientation (see Section 2.2.4),

structural modifications of these Polycarbonate films do not seem important '! n

modifying dielectric loss at cryogenic temperatures.

1.3.2 Nylon 11

Only one type of Nylon 11 film, the Nylon 11-A was measured. This was a

poorly crystalline sample (see Section 2.2.3). The film was 40 ym thick. The

data are presented in Table II and Figure 4.

The loss behavior of the Nylon 11-A studied here is quite different from any

of the other polymers studied to date. The loss near room temperature is much

larger than any of the other polymers but decreases very rapidly with decreasing

_ 6

temperature. By 30 K tan 6 has become 30 x 10 and between 4 to 10 K tan 6 has

become 20 x 10 With the decrease in loss, the dielectric constant has decreased

from 3.0 to 2.5 at cryogenic temperatures. Therefore, in terms of dielectric properties, the Nylon 11 changes from a poor material at room temperature to one that

meets the desired criteria at the operating temperature of the superconducting cable.

No further work was done on Nylon 11 due to the unavailability of samples

with suitable mechanical properties. However, the data determined here suggests

that if a film could be found that is suitable mechanically, it could be suitable

electrically.

1.3.3 Polysulfone

Only one type of polysulfone, the Polysulfone-A which is a highly transparent

film 50 ym thick was measured. The data for this material are shown together with

the Nylon 11-A data in Table II and Figure 4.
0001

62 -

gOI X 8 m

o

O

m o

90IX8 UD|

Figure

4;

Tan

6

vs.

temperature

at

100

Hz.

The

circles

are

for

Nylon

11-A,

the

squares

for

Polysulfone-
63 -

The loss data show a very broad peak around 200 K at 100 Hz. The peak is

so broad in a temperature sense that it persists down to the lowest temperature

attained, 4.2 K. The loss mechanism is also very broad with respect to frequency

as seen in the near equality of the 100 Hz and 1 kHz data (see Table II). Tan 6

varied from 70 to 110 x 10 ^ in the temperature range of 4.2 to 10 K which is

clearly much too high for the power cable requirements.

1.3.4 Polyethylene

A larger number of measurements were made on many different samples of polyethylene. The samples measured include the Polyethy lene-A film (26 ym thick) for

which data were collected from both single and double layers, the Polyethy lene-C

and Polyethylene-D films (100 ym thick) , and a series of polyethylene sheets

specially prepared for BNL (Polyethy lene-BNL, see later and Table III). The data are

given in Tables IV and V and Figures 5 and 6. Significant differences in dielectric

behavior were found in the different samples of polyethylene. These differences

will be pointed out in the following discussion.

The Polyethy lene-A was measured both as single layers and double layers.

Within experimental accuracy, the data for the double layers were the same as the

single layers and, therefore, no separate data will be given for the double layers.

This shows that for these films, the presence of an additional interface was not

enough to influence the measurements.

At 100 Hz the loss data for the Polyethylene-A film show a loss peak at about

175 K, a slight rise in loss with temperature beginning at 250 K, and a low level of

__ ^ loss at all temperatures. The loss at 100 Hz below 10 K was constant at 6 x 10

which is well below the desired maximum. The 1 kHz data do show a slight rise at

4.2 K but are still quite low. As for all polyethy lenes , the dielectric constant

is always lower than the desired maximum of 2.5.
64

90lx8 udj.

o

o

o

o

ro

O

O

OJ

O

o

9 0IX8UDI

Figure

5:

Tan

6

vs.

temperature

at

100

Hz

for

various

polyethy

lenes

.

Circles

represent

Polyethylene-.

diamonds

Polyethy

lene-C,

squares

Polyethy

lene-D,

triangles

Polyethylene-BNL-2.

The

circle

inside

the

square

symbol

represents

overlapping

data.
- 65 - Ii

CO

a)

1“

od

•HO•

l-l MW

CD i—1 -O

cd Hd

•H • CN T3 1 QJ •U §

CO PQ •H

r—

CO

CO QJ

ai

d 1—

cO ex 3 s cr

cd CO

CO T)d § co PQl0)d 1 a) l_3 i—i >» PQ X4-1 QJ n

td

d i—1 o O

CU §

•H

CO to 3o #s r^.

S-i 1 cd>

pq

do

M-t co

QJ

N id

00d

O co o •H 1—1 d

4J

4-1 CO #\ OO

0) 1 d3 2 4-> PQ

CO

!-l 0) 0) i—l CX ex e E

qj CO

4-1 CO • 4-1 CO d > 0)co <o Q)d d cx

CO QJ H d

0)u3

00

•H
66 -

The Polyethy lene-C film shows an additional loss peak compared with the

Polyethylene-A at 260 K and generally higher loss levels above 125 K, but below

125 K, it seems indistinguishable from the Polyethy lene-A. The Polyethylene-D

film differs from the Polyethylene-A film even more. Above 125 K the loss is

similar but larger than that of the Polyethy lene-C. As the temperature decreases

— ft below 10 K the 100 Hz loss rises to a tan 6 of 12 x 10 and the 1 kHz loss to

__ g a tan 6 of 33 x 10 . This indicates that there is a definite loss peak in the

Polyethylene-D below 4.2 K although the loss level in both the C and D films

remains suitable at the power cable operating temperatures.

The other polyethylene samples measured consisted of 14 sheets (each about

200 ym thick) prepared from the same linear polyethylene polymer by Battelle for

BNL. The sheets differed in that they had various amounts of antioxidant added

and some were subsequently subjected to 24 hour extraction in different boiling

solvents. The Polyethy lene-BNL samples are listed in Table III. Sample BNL-2

was taken as characteristic of the base polymer for illustration in Figure 5. This

film showed a very low loss level at all temperatures, no indication of increasing

V

loss at room temperature, and a reduced peak at 150 K. The low temperature data

were similar to the Polyethylene-A data below 55 K except for a rise in tan 6 at 1

kHz below 6 K. In terms of dielectric properties, it too met all criteria.

The data for all the Polyethy lene-BNL samples are given in Table V and representative data are illustrated in Figure 6. Because only single samples of each

of the different sheets were measured and because their surfaces were not very flat,

the loss data show additional scatter. Also, some of the samples had noticeable

surface layers that were not easily removed with an acetone-ethanol-distilled water

rinse which was given to all the samples. Some of the sheets had noticeable inclusions but they were avoided, when possible, in cutting the discs used in the cell

and did not seem to effect the measurements.
67 -

Samples BNL-1 and BNL-2 are made from the base polymer which contains only

the antioxidant present in the original polymer, 0.015% These two samples

show the presence of a loss peak below 4 K, with the unextracted BNL-1 having

somewhat more loss. Both samples are very similar in behavior to previous samples

of polyethylene. The other unextracted samples, which have antioxidants XX, YY

,

and ZZ added, all have enhanced low temperature loss with the peak still being

below 4 K. The loss, with one exception is proportional to the additive content

and similar for all three additives. The exception is that the samples which had

0.1% antioxidant added seem to act as if they had only 0.05% antioxidant. DSC

data^ behaved in a like manner, so that this exceptional behavior of the 0.1%

additive content samples could be an artifact of the way the samples were prepared.

The data on the BNL samples show that the presence of antioxidant in polyethylene can give rise to enhanced loss in polyethylene at cryogenic temperatures.

The loss peak is below 4 K at the frequencies used here and is quite sharp with

respect to frequency. It is not as sharp as a Debye loss peak, however, as can

be seen by comparing the 100 Hz and 1 kHz data. For a Debye loss peak tan 6 would be

proportional to frequency in the low frequency wing, whereas the data for sample BNL

at 8 K show that the loss at 1 kHz is larger than that at 100 Hz by a factor of

6 rather than 10. Compared to normal polymer loss peaks, though, the loss peak

below 4 K is still very sharp. Also, this enhanced loss is confined to low

temperatures. Data on sample BNL-8, which shows the largest loss peak at cryogenic

temperatures, were obtained over the entire temperature range. When the temperature

was 80 K and above, the loss was very similar to that for sample BNL-2 which had

the lowest loss at cryogenic temperatures of all the BNL samples. Thus at low

frequencies, antioxidants seem to affect tan 6 only at cryogenic temperatures.
68 -

Solvent extraction with methanol and cyclohexane does reduce the low

temperature loss caused by the addition of antioxidant. For the one sample for

which there is data, cyclohexane seems to reduce the loss to that of the original

polymer while for the others with methanol the additional loss is reduced by about

half. This loss reduction is seen even in the base polymer, thus sample BNL-2, which

was extracted in methanol, has lower loss than sample BNL-1, which was not. Since

the original polymer contained antioxidant, this loss reduction is also related

to the antioxidant content.

1.3.5 Polypropylene

Four different polypropylene films were measured. They are identified as

Polypropy lene-A, B, C, and D, respectively. The A and B samples were nominally

the same except for surface treatment, the B having been corona treated. As the

A and B films appeared identical, only the data for the A film will be mentioned.

The sample thicknesses were A (27 ym) , C (130 ym) , and D (33 ym) . The data are

presented in Table VI and Figure 7.

Even more than in polyethylene, the loss data are quite different for the

different polypropylene samples. This is true throughout the entire temperature

range. The data for Polypropy lene-C, a film with low crystallinity (see Section

2.2.2b) show the beginning of a loss peak above room temperature, a loss peak at

_ g 120 K and a decrease in tan 6 with decreasing temperature to about 10 x 10

at 10 K and below. There is no evidence of a low temperature loss peak.
200

69

9

0l x § ud|

o

o

H

o o o o

t ro N -

gPI X §UDj

Figure

7:

Tan

6

vs.

temperature

at

100

Hz

for

various

polypropylenes.

The

squares

represent

Polypropy

lenethe

circles

Polypropy

lene-C,

and

the

triangles

Polypropy

lene-D.
70 -

Polyp ropylene-A shows just a gradual decline in tan 6 from 30 x 10 at

_6

room temperature to 9 x 10 at 30 K. The loss peak at 120 K exhibited by the

Polypropy lene-C seems to be completely supressed. As in the polyethy lenes

,

_ £

there is a low temperature loss peak below 4 K and the loss rises to 32 x 10

at 4.2 K at 100 Hz. Thus, at 100 Hz the low temperature loss becomes equal to

the room temperature loss, and it even exceeds it at 1 kHz.

The loss data for Polypropylene-D is different still. The loss peaks found

in the Polypropy lene-C are present except that the room temperature loss is somewhat less, and the 120 K peak a little more. In the D sample a new broad loss

peak appears at 30 K that seems to persist down to 4 K. There is no evidence of

_ 5 a loss peak below 4 K, but tan 6 stays between 20 to 30 x 10 throughout the

superconducting cable temperature range, making this polymer acceptable in terms

of loss.

1. 4 Discussion

The loss data for polycarbonate, polysulfone and Nylon 11 do not need much

explanation. Only a few samples were measured for each and they are not currently

( 2 ) favored candidates for the power cable insulation . The reasons range from poor

mechanical properties in the case of Nylon 11 to poor electrical behavior for the

others. Note that not many different forms of these polymers were available to

show the kinds of differences that were found in polyethylene and polypropylene.

Polyethylene and polypropylene do warrant some extended discussion. Both

polymers are considered to be low loss materials but the data show considerable

differences in behavior throughout the temperature range. While many of the film

samples seem to have very acceptable values of tan 6 at cryogenic temperatures two

samples approach the limit of acceptability and one of the two (Polypropylene-A)

even has a higher loss at 4 K than at room temperature.
71

All the polyethylene films (A, C, D) and the Polypropy lene-A showed at least

a hint of a loss peak below 4 K. From the data on the Polyethy lene-BNL samples,

it is clear that the addition of antioxidants to polyethylene can give rise to

( 3 ) such loss. This confirms, in a systematic manner, previous work . Also the

data suggest that the loss can get excessive at the cable operation temperatures.

Furthermore, solvent extraction does reduce this source of loss. From the similarities in behavior, the appearance of a low temperature loss peak in all the polyethylene films and the Polypropylene-A can be assumed to be due to the presence

of antioxidants.

Questions still remain with respect to antioxidants without even worrying

about possible mechanisms. It is not as yet known whether there is any interaction

between the polymer structure and the antioxidant content which affects the magnitude

of the loss. It should be noted in this regard that when more highly oriented films

having better mechanical properties become available, the possibility should be

examined of whether they exhibit enhanced antioxidant induced loss. The present

data are not able to answer this question.

The ability of solvent extraction to reduce the loss attributed to antioxidant

is also a little puzzling in one respect. The use of chromatography seems to indicate

that no more than 30% of the antioxidant was ever removed by extraction^"*") . This is

not enough to account for the reduction in loss seen here or the change in DSC data^"*")

Attempts to monitor the antioxidant concentration by infrared and Raman spectroscopy

at NBS were unsuccessful. If the chromatography results are correct, it is suggestive

that the antioxidant effects are surface related. The current measurements are unable

to answer this question.
72

For Polypropylene-D , the loss below 10 K does not seem to be related to the

presence of antioxidants. There is no indication of a peak below 4 K as seen

in other samples. Rather tan 6 is almost constant between 4.2 to 10 K. Also,

the level of loss was higher between 6-8 K than any other polyethylene or polypropylene. If the possible antioxidant contribution is ignored, the loss below

10 K seems to be connected with a broad, weak loss peak near 30 K. This peak has

( 4 ) been seen before in mechanical measurements but its origin is unknown. It is

possible that this loss peak is related to the structure of this film, (see Section

2.2.2c), but further work will have to be done to verify this. The results for

Polypropylene-D do suggest that there are sources of loss at cryogenic temperatures

that are not due to antioxidant level and could be troublesome.

1 . 5 Summary

The measurements of e and tan 6 on the polymer films looked at show that it is

possible to meet the requirements for the insulation in superconducting power cable

with polyethylene, polypropylene, and Nylon 11. However, the measurements also show

that it is possible to get excessive loss in these materials. Any modifications

made to these polymers to enhance their mechanical properties will have to be

examined for the possibility that they might affect their dielectric properties

adversely
73 -

2. Aspects of the Fine Structures of Polymer Tapes (F. Khourv, J.P. Colson, L.H. Bolz)

2.1. Introduction

The purpose of the work described in this section was to establish some background knowledge of aspects of the fine structure of the various polymer tapes whose

dielectric and mechanical properties are being investigated as part of the ongoing

screening process aimed at selecting tapes which are suitable for use as insulation

in Nb^Sn superconducting cables.

Tapes which are slit from commercially available polypropylene, Nylon 11, polycarbonate and polyethylene films are at present being evaluated for use in the cables

One aspect of the evaluation process is to compare the dielectric and mechanical

properties of different tapes made from each of these polymers, the aim being to

find whether any tape made from one of these polymers exhibits optimum dielectric

and mechanical characteristics. The reasons for undertaking a concurrent examinatieof the fine structure of the tapes are outlined below.

The structure of polymer films can vary widely with respect to the overall

crystallinity of the film, the orientation of the crystallites in the film, the manifestation of chain-folding in the crystallites, and the occurence and tightness of

tie molecules between neighboring crystallites. These various features are governed

by the conditions under which the polymer crystallizes and the extent to which it is

subjected, as is usual in film manufacture, to orientation inducing processes such

as uniaxial or biaxial stretching or rolling Furthermore, the dielectric loss

characteristics and, more particularly, the mechanical properties of polymers are

/ £ \ sensitively structure dependent v

. Thus, dielectric and mechanical losses can

vary depending on the crystallinity of the polymer sample, and the tensile modulus
74 -

of polymer samples in which the crystalline regions are unoriented can be as -2

much as two orders of magnitude smaller (x 10 ) than that in a sample in which

the crystalline regions are highly oriented with the chain molecules parallel to

the straining direction. Accordingly, knowledge of the respective structures of

different tapes made from the same polymer provides a basis for analyzing their

physical properties, for assessing the possible origins of differences between

their dielectric and/or mechanical properties, and for establishing guidelines on

how the fine structure of the tapes could be controlled at the film manufacturing

stage so as to optimize these properties. It should be noted in this connection

that the physical properties of the tapes are not only of importance with regard

to the functions of the tapes at cryogenic temperatures. The success of the polymer

tape winding operation in the manufacture of the cables is critically dependent on

the mechanical properties of the tapes at room temperature.

The main objective of our work at this exploratory stage has been to examine

the nature of the orientations of the crystallites (crystalline orientation) in the

tapes and to characterize, qualitatively, salient differences in orientation among

the tapes. To this end, wide angle x-ray differaction (WAXD) has been used as a

probe which, as will be seen, has also served to identify tapes having relatively

poor crystallinities. In addition, small angle x-ray diffraction (SAXD) data have

been obtained which pertain to the manifestation of chain-folding in the crystallites

and which also have a bearing on the crystalline orientation in the tapes.

Apart from their dielectric and mechanical properties, there are other aspects

of the polymer tapes which are being investigated at BNL and other laboratories in

connection with either the cable manufacturing process (the tape winding operation)

or the performance of the cables in end use. Two of these aspects are the frictional

properties of the tapes, and the radial thermal conductivity at cryogenic temperatures
75 -

of the helium bathed (-0.5-1") thick layer of polymer tapes wound spirally around

the core of the superconducting cable. A feature of interest in connection with

both of these aspects is the nature of the interface between successive layers of

tape. Some observations on the surface textures of a few of the polymer tapes are

summarized in the last section of this report.

All of the tapes which have been studied were supplied by BNL.

2 . 2 Crystalline Orientation and Order in the Tapes

2.2.1 Background and Experimental

Wide angle x-ray diffraction (WAXD see Glossary) patterns were recorded using

O a flat film camera and Ni-filtered CuKa (A=1.5418A) radiation. Diffraction patterns

were obtained with the x-ray beam oriented parallel to three different directions

in each tape. These directions which are identified in Fig. 8, are the machine

direction M (i.e., the direction parallel to the long axis of the tape), the transverse or edge-on direction T which is a right angle to M and parallel to the plane

of the tape, and N which is perpendicular to the plane of the tape. From a comparison

of the wide angle x-ray diffraction patterns obtained in these three directions,

deductions were made concerning the main characteristics of the crystalline orientation in the tapes, i.e. the preferred orientation (s ) of the constituent crystallites

in the tapes.

In addition to the wide angle x-ray diffraction experiments, small angle x-ray

diffraction (SAXD see Glossary) patterns of some of the tapes were recorded (on

photographic film) using a small angle x-ray camera with pin-hole collimation and

Ni-filtered CuKa radiation. These SAXD patterns were examined for the presence of

discrete diffraction rings, arcs, or spots corresponding to spacings in the range

O 50-400A, the latter dimension being near the limit of resolution of the instrument.
76

Figure

8:

Identification

of

the

axes

of

reference

in

the

tapes. M

is

parallel

to

the

machine

direction

which

corresponds

to

the

long

axis

of

the

tape. T

is

the

transverse

direction

which

is

at

right

angles

to

M

and

parallel

to

the

plane

of

the

tape. N

is

normal

to

the

plane

of

the

tape.
77 -

Briefly, the manifestation of such features is generally taken as evidence for

the occurrence of chain folding in the crystallites. Furthermore, since in the

simplest cases the chain molecules and hence the c-axis tend to be oriented at

right angles to the fold surfaces of the crystallites information concerning the

crystalline orientation in the tapes can also be derived from SAXD patterns. This

latter type of information complements that obtained from WAXD patterns.

The density of some of the polyolefin tapes was measured using a water/ethyl

alcohol density gradient column kept at 296 K. These measurements remain to be

checked for reproducibility; we nevertheless include them subject to duplicate

determinations

2.2.2 Polypropylene Tapes (Polypropy lene-A, B. C, D, E)

The most common unit cell structure of isotactic (see Glossary) polypropylene

o o is monoclinic (see Glossary). The unit cell parameters are a = 6.65A, b = 20.96A,

c = 6.5A, b = 99°20*

,

and this cell is usually referred to as the a-monoclinic

cell. Four chain molecules pass through the cell. The axis of each of these helical

molecules is oriented parallel to the c-axis of the unit cell.

As an introduction to the crystalline orientations exhibited in the tapes the

following characteristics of the manifestation of orientation in stretched polypropylene samples may be pointed out.

In common with other crystalline polymers, stretching polypropylene along one

particular direction (uniaxial stretching) causes the crystallites to be oriented

with their c-axis (which is parallel to the chain molecules) preferentially parallel

to the stretching direction, the orientation of the crystallites is otherwise randomized in a cy lindrically symmetrical manner about that direction. We shall refer
- 78

to this type of orientation as c-axis orientation . Fig. 9a represents the WAXD

pattern which would be obtained with the x-ray beam oriented at right angles to

the stretching direction in an idealized sample having perfect c— axis orientation

parallel to the stretching direction. The calculated^ dispositions of the diffraction spots corresponding to the (110) , (040) , (130) , (111) , (131) and (041)

crystal planes are indicated in the diagram as they would be recorded on a flat

photographic film. A peculiarity of uniaxially stretched polypropylene should be

noted, however. Thus, in addition to the manifestation of c-axis orientation

parallel to the stretching direction and depending on the extent of stretching,

on the thermal conditions under which stretching takes place, and on thermal aftertreatments, a varying but usually relatively minor proportion of the crystallites

in uniaxially stretched samples are oriented with their a-axis (or possibly the

a'-axis, where a' is the projection of the a-axis onto the plane perpendicular to

the c-axis) parallel to the stretching direction^

The orientation of this

latter population of crystallites is otherwise randomized in a cy lindrically symmetrical fashion about the stretching direction. We shall refer to this type of

orientation as a-axis orientation , and Fig. 9b represents the corresponding calculated WAXD pattern.

The simultaneous occurence of two populations of crystallites, one with c-axis

orientation and the other with a-axis orientation , both parallel to the stretching

direction in uniaxially stretched polypropylene is believed to be a consequence of,

or related to, a mode of twinned crystal growth which is unique to polypropylene.

The main feature of this twinning phenomenon is that the c-axis in one twin is

parallel to the a-axis in its companion, the b-axis in each twin being parallel to

that in its companion

We shall not attempt to discuss current views on the
79

£

e 3 cd CO 3

<u CD 3 3

4J -CJ 4-J

X

•H •H

t-H r-H > i—

cd i—3 3 !h 3 54 u 1 4-J 1 CO X CO X

>.G CD 54 3 o X O -C H H

0) 3 G X H • H • £ g cd 3 • G • 54 00 —

00

4-J cd 4-1 3 x •H X •rH CD X 3 X) u 4-1 a) 3

0)

X 3 X • • 0) u 3 4J c CO CO

•rH

N—' C

G

•H •rH 3 a c c o c o c o •rH O •H o

•H 4-J •rH 4-J •r-f 4-1 cd 4-J 3 4-J o u CJ 4-J a 3 c 0) c 3 i—

a) >H 3 54

<4-1 •H •H •rH •rH 01 G X 54 X G O O

t-H i—1 i—

CO cd 3 3

<r •rH CJ •H 3 o X •H X •H

cd 4-J 3 -U

x i Jo 1 54 C o 0) 3 3 3 > >

00 00

#»

c ai

C 3

t-H •H -C

X 00 > 4-J > 4-J 1 1 cd 3 X o -G o

r» 4-J 4-1 i—1 0) 3 I 1 i—

i—1 i—1 t—1 t 1 a a) CO 3 £ i—

• cl T 1 •

e*' cd

t 1 CDT i CD

o CO cd 54 3 3 U

CO 5-J 3 G

D

T

—

0) cd oo 3 3 60 c co •rH C CO •H

r» 0) OH 3 M-l o i—

CO t-H 3

<3* >H •rH <D >. •rH CD o CO X -G CO X o Cd 4-1 o 3 •U

rt So 1 54 1 o CO a M—

CO 3 M-l

T 1 >T

O >,

O 1 1 t 1 5h r—t 5-4 o •rH 3 o •rH CD CO CD C CO 3 C O X cd -G Cd cd 4J i—

3 4-J t-H CO CO Cu c 4H -G C4H rC o o 4-J 3 o u 0) •H •H •rH rC

4-J

G

s 4-1

G 4-J •H So 54

CO CD XIo 3 X

o

O 4-1 CD 4J 4-J 3 -U Cu 4-1 4-J 4-J 4J

CO cd

G i—

3 G i—1 •H a. CD cd CO 3 Cd U •H •H j~ Q G 5-t Q G U >< O O >< O O

CD *3

C < C

4-J 0) 3

ctf 5-J CO

G CO

t

—

< cd •rH < 3 •H P31 1 r—s r~\ 3 3 U ^ ^

CT\3

!-i P

OO

•H

li
80 -

* , (H-13) _ , ... . . origins of this phenomenon . It is sufficient in the present context to

note that composite WAXD patterns corresponding to a parallel superposition of

the two patterns depicted in Fig. 9 are often exhibited by uniaxial stretched

polypropylene samples. In actuality, of course, diffraction arcs rather than

sharp spots are observed in experimental WAXD patterns due to deviations among

the crystallites from the idealized orientations represented in Fig. 9.

More intricate orientations or mixtures of orientations than occur in uniaxially stretched samples are manifested in samples subjected to more complicated

stretching regimes, e.g. simultaneous or stepped biaxial stretching (balanced

. . (14-17) .. ... (18) . . . . (19)

or unbalanced), cold rolling, or uniaxial compression

Confining our remarks to the case of biaxial stretching, it is sufficient

for our present purpose to indicate, with reference to Figs. 10a and 10b, two

preferred types of crystallite orientation which have been reported to occur

simultaneously (and in some cases in combination with both c-axis and a-axis

orientations ) in biaxially stretched films .

Adopting a nomenclature used by Adams, t^e ori entation illustrated in

Fig. 10a will be referred to as (040) planar orientation . This designation identifies a population of crystallites in which the (040) planes are parallel to the

plane (MT) of the film. The b-axis in these crystallites is parallel to N, their

orientations are otherwise randomized in a cy lindrically symmetrical fashion about

N. It follows that the c-axis in the crystallites is parallel to the plane (MT) of

the film, but there is no net preferred orientation of the c-axis along any direction

in that plane. Fig. 10a represents the calculated dispositons of the 110, 040, 130,

111, 131, and 041 diffraction spots in a WAXD pattern taken with the x-ray beam

parallel to either T or M (or any direction parallel to the MT plane) in a film

exhibiting (040) planar orientation .
81

CO

cd

4-1 4-1 <d •rH X (n i—

CD CO u i—

4-1

d CO CD P 00 4J CD rC

a)

e CO CD 4-J •u •rH Sp CO CD +j > U O P

cO cO

O 4-J cO a, x. CD i—

a)

P T—

a,

o

W rd cO a) >< e 4-4 i—

rH

H i—

CL i—

IS •H P cO MH •H Fh P CD

d cO rC

•H

£ CO P- 4-1 CD CD

w

e rC nd

o

C a) cO 4~> CD 4-1 o £ i—

4-J •H cti p- o p i—

4-J rH 4-) CD CO a C4 ^ N •rH b

<Do rH

p

P

rH F—

<r 03

O

O

4-1 jEl

o

&

P

CD

S'—'

P CD

P CD

O

P CD rd CD d co P i—

4-1

& cO <3" 4-J CO CO O o •H CD CO

4-J r>

d CD "d £ CO co X c i

1 o •rH rH cO

cO CD •H

X Pr

t

—

4-J CO 0) i—1 03 1 r

~*~' CD rH CO 4-J X o •rH CO P £ t—1 4-> i—1 cO (D CD i—

4-J CD •H -d ^ CO H 4-J i—

rH

c

O CD 1—1 o to jc i—

\—

•rH

U

d 4-j CO

4-J 03 co

o

a

£ r>

o

o CD o3

B

d

p

CO

P «—

H

o P<

t

—1 •H P. •H *rH •rH nd 4H 4-1 U

/^S cO <D

o

o CD 4-)

P

<r

c -dd

o cOo 4J CD •K

•rH i—

p PH P O

o

o

O

O rH

t

—

/* i—

1—

CO CD

P 1 H 1 d cO

co

d

P

o <?\ • • i—1 cO

O «—

S co P- rH t—

d P- *

00

o

H r—

CD

d •rH IS

O

o 4-1o i—

4-J i—

CO CD i

i i—

cfl 4-J rd rH v—

4H

d 4J •—

O

B CD CD cO •rH o rd

0) a)

P 4-1 4->

£ rd

o rO

o I—

Hd

•H CD CDd

•U C0 > i—

cO •H P •H i—1 •

CO 1 4-J cO /-v

B

O

X

o

P co rH

o. CD cO i—

•rH CO CD ft a-H <4H •H -d CO cO r‘d 4-J CD Hd 4H CD P CD CD rd • XJ rd 4J TO 4-1 /—

CD 4-J oo

d 4-j

4-J •H

£ (D CD <4H

X

03 •H •p

pO CD rH £ P o 4-J £ d o O B CD a CD rH d (D rH rX rH CD P cO (D

03 COO

P

O

t

—

c

n

o 4J 4H CO cw p< o1—

<DPP

00

•rH pH
82 -

The orientation illustrated in Fig. 10b, referred to as {110} planar

(17) orientation, identifies a population of crystallites in which {110} planes

i.e., the (110) or the (110) planes) are parallel to the plane (MT) of the film.

Correspondingly, the [110]* or the [llo]* reciprocal lattice axes in the crystallites are parallel to N and the orientations of the crystallites are otherwise

randomized in a cylindrically symmetrical fashion about N. In addition the c-axis

in the crystallites is oriented parallel to the (MT) plane of the film. Fig. 10b

represents the calculated dispositions of the 110, 110, 040, 130, 111, 131, and

041 diffraction spots in a WAXD pattern taken with the x-ray beam parallel to

either T or M (or any direction parallel to the MT plane) in a film exhibiting

{110} planar orientation .

M-axis or T-axis WAXD patterns obtained from a film in which both the (040)

planar and the {110} planar orientations are manifested, would correspond to a

parallel superposition of the calculated patterns shown in Fig. 10a and Fig. 10b.

In actuality, due to deviations from the perfect orientations depicted in Fig. 10

the reflections will be arced. The orientations depicted in Fig. 10 represent in

fact the preferred orientations of the crystallites and correspond to peaks in the

distribution of crystallite orientations in the films. There is another feature

of the diagram depicted in Figs. 10a and 10b which should be pointed out. In the

case of perfect (040) planar orientation , the (040) planes which are oriented

parallel to the plane of the film will not satisfy the Bragg conditions for diffraction when the x-ray beam is parallel to M or T, so that the (040) reflections

which are situated along N in Fig. 10a should have been omitted in principle. The

same consideration applies for the 110 reflections situated along N in the case of

{110} planar orientation depicted in Fig. 10b. Due to the distribution in the
83 -

orientations of the (040) and (110) planes in the crystallites relative to the

ideal orientations represented in Figs. 10a and 10b respectively, one would expect

M-axis or T-axis diffraction patterns from films to exhibit in practice 040

reflections along N. corresponding to preferred (040) planar orientation , and 110

reflections also along N, corresponding to preferred {110} planar orientation .

We have therefore marked the dispositions of these reflections in the respective

diagrams since they are to be expected, and are indeed observed diagnostic features

2.2.2a Polyp ropy lene-A and Polypropylene

Since the WAXD patterns exhibited by the Polypropy lene-A tape were similar to

those obtained from the Polypropylene-B , we illustrate in Fig. 11 examples from the

former tape only. The patterns may be indexed according to the a-monoclinic unit

cell of polypropylene. The following features may be noted in Fig. 11:

(i) The M-axis WAXD pattern (i.e., diffraction pattern with the x-ray beam

parallel to M in Fig. 11a, and the T-axis WAXD pattern in Fig. lib, in both of

which the reflections are distinctly arced, are essentailly indistinguishable from

one another. This feature taken together with the ringed character of the N-axis

WAXD pattern, Fig. 11c, strongly suggests the existence of a crystalline orientation,

or orientations, which are cy lindrically symmetrical about N.

(ii) Intense 110 and 040 arcs occur along N in both Fig. 11a and Fig. lib. From

a consideration of Fig. 10, it can be seen that these two features are consistent

with the occurence of preferential (110 planar orientation and preferential 040

planar orientation respectively in the tape.

(iii) Considering the case of 040 planar orientation first, it can be seen from

Fig. 10a that one would expect the occurence of 110 arcs situated along two diameters

oriented at close to + 72.5° relative to N in both M and T axis WAXD patterns. Such

arcs are present in Figs. 11a and lib. Examination of Fig. 10a also shows that one
84

e

CUe

•H

CJ

0)&

to

o

00c

<U (0 W O c e

rH

W

<DCC

Figure

11:

(a)

M-axis,

(b)

T-axis,

(c)

N-axis,

WAXD

patterns

from

the

Polypropylene-A

tape.

The

film

distances

were

not

identical.

These

are

contact

prints

of

the

originals.

The t1

arcs

situated

along N

in

(a)

and

(b)

are

110

and

040

reflections

respectively.

The i

in

(c)

is

the

110

ring.
85 -

would expect 111 arcs to occur along two diameters oriented at close to + 78°

relative to N. Although faint, such arcs can be discerned in both Figs. 11a

and lib - they were clearly evident in the original films. In short, the

features indicated above are consistent with and indeed confirm the occurrence

in the tape of a population of crystallites having preferential (040) planar

orientation .

(iv) Turning to the case of (110) planar orientation , it can be seen from Fig.

10b that one would expect 040 arcs to occur along two diameters oriented at close

to + 72.5° relative to N in both T-axis and M-axis WAXD patterns. Such arcs are

present in Figs. 11a, and lib. A consideration of Fig. 10b also indicates that

one would expect the occurences of 110 arcs along diameters oriented at + 34°

relative to N. No such discrete arcs can be convincingly resolved in Figs. 11a

and lib. This may be attributed to the merging of these arcs with the 110 arcs

situated along N, and the 110 arcs situated along diameters at +72.5° to N which

were identified above as resulting from (040) plane orientation . Such merging would

account for the apparent continuity between these last two sets of arcs. This consideration and the clearer evidence provided by the occurrence of the 110 arcs along

N and 040 arcs along diameters at + 72.5° to N certainly point to the occurrence in

the tape of a population of crystallites having preferentail {110} planar orientation .

We shall not attempt to analyze and discuss the diffraction patterns further,

except to point out that a consideration of the patterns in Figs. 11a and lib in

the light of the calculated patterns shown in Fig. 10 with reference to the dispositions of the (130) , (131) and (041) reflections arising from both (040) and

(110) planar orientations , confirms the deductions pointed out above, namely that

two identifiable populations of crystallites, one with preferred ( 040 planar orientation

and one with preferred {110} planar orientation , occur in the Polypropylene-A and
86 -

Polyp ropy lene-B tapes. It must, however, be emphasized that these two orientations

are preferred orientations and that, as evidenced by the arced character of the

reflections and continuities between others due to apparent overlaps, appreciable

deviations from the idealized cases represented in Fig. 10 occur among the crystallites.

A SAXD pattern was taken with the x-ray beam parallel to N in the Polypropy lene-A

tape, no small angle reflections could be discerned in the photographic film. This

may be due to a broad distribution of fold periods in the crystallites. Annealing

the tapes at elevated temperatures and examination of the SAXD patterns exhibited

by the annealed specimens would shed further light on this matter which is however

not being pursued at this juncture.

Finally, the density of a sample of the Polypropylene-A tape and one from the

Polypropy lene-B tape were measured and found to be 0.904,. and 0.904^ respectively.

These values correspond to a weight fraction crystallinity of 0.63.

2.2.2b Polypropy lene-C

No detectable evidence of crystalline orientation was observed in the WAXD

patterns obtained from this type of tape. In addition, the WAXD patterns were

indicative of poor crystalline order. The patterns differed from the type of pattern

expected for unoriented a-monoclinic polypropylene. Fig. 12a represents a diffraction

pattern obtained with the x-ray beam parallel to N. A diffraction pattern from the

same tape after it had been annealed at 413 K for two hours is shown in Fig. 12b,

the x-ray beam was also parallel to N in this case. The powder (ringed) type pattern

exhibited by the annealed sample is typical of a-monoclinic polypropylene as evidenced

by the five distinct rings which, proceeding from the inner ring outwards, can be

identified as the 110, the 040, the 130, the 111 and the composite 131, 041 diffraction

rings. In contrast, the pattern from the unannealed (as received) tape shown in

Fig. 12a exhibits what appears, at first examination, to be only two diffuse rings
87 !i o

CD CO Co 3

cO 3

4-1 3

44

CD 44 e 4J 3

cO

o CO

co

G 3

CD CD

X

X >4 44

4-1 CD5 3 B 3 o N 3 3 X s

<4-1 '—

443 G XI X 3 3

<D cO 3

4-1

O

4-1

f

N 3

CO CO •H

CO

—• 33 n f4 CD O B

<d 44

o

co

a

CO 3 3

•H CJ

o

X 3 44

cO 3 1 4-1 44 3 CO X

•rH 3 ^—

X 44 rd' ' B 3 1—

3

•H 3 • 44

CDa

O 3

co 44 i—

4-1 3 3 3 u 3 •H 1 e 00 • CD •H •H 3 c CJ 3 CO 3 CD O 3 ,—

CO 44

>-, cn 3

co

X

X

o 44 3

>4 • rH

co CO 44 3 3 O 3

rH 3 3 0 o

Pu

X

01

O

•P 4-1 B U o o 3 44

04

i4

G3 co

0) ,—

4-1 <f

4-1 CO 4-1 CO ns o £>o § -H * 3

CO 3

•H 33

CO

CO 3

4-1 CO c 3

•H 3

>4CO

CJ

cO

4-1 3O3

0)3

CO

OJCO

0) X I 53 " CO rH *H

CO

X

CJ CO •H | *-> 3 3

CD

\ TO CJ •H

CN

CD33

00

•H

ft,

SAXD

pattern

of

the
88 -

corresponding to spacings of ~4A and ~6A. Upon closer examination it appears that

the inner ring is a composite of a relatively sharp and a more diffuse ring. It

may be concluded that the crystalline order in the tape, as received, lies between

that of the smectic mesomorphous state of polypropylene (which state of order

occurs when the polymer is rapidly cooled from the molten state) and the ot-monoclinic crystalline form associated with samples crystallized or annealed at relatively

elevated temperatures.

The density of a sample of the unannealed tape was found to be 0.884^ which

corresponds to a weight fraction crystallinity of 0.39. This low crystallinity is

consistent with the WAXD results described above.

A SAXD pattern obtained from the unannealed (as received) tape with the x-ray

beam parallel to N is shown in Fig. 12c in which a readily distinguishable diffraction

O ring can be seen. This ring corresponds to a spacing of 110 A. The occurrence of

such a diffraction ring is consistent with the presence of a chain-folded lamellar

morphology and a random orientation of the lamellae in the tape. This latter

feature is in turn consistent with the absence of evidence for crystalline orientation in the WAXD patterns.

2.2.2c Polypropy lene-D

The M-axis, T-axis and N-axis WAXD patterns obtained from this tape are shown

in Figs. 13a, 13b, and 13c respectively. These patterns can be indexed according

to the a-monoclinic unit cell of polypropylene. Conciseness and simplicity in

description are better served in this case by first summarizing the conclusions

concerning the orientation characteristics of this tape. The evidence, based on

Fig. 13, will subsequently be described.
89

Figure

13:

(a)

M-axis,

(b)

T—

axis,

(c)

N—

axis

WAXD

patterns

from

the

Polyp

ropy

lene-D

tape.

The

specimen

to

film

distances

are

not

identical,

these

are

contact

prints

of

the

originals.

The

three

intense

arcs

situated

along

N

in

(a)

and

M

in

(c)

are

the

110,

040

and

130

reflections

respectively.

The

three

innermost

rings

in

(b)

are

110,

040

and

130

rings.

(d)

N-axis

SAXD

pattern

from

the

same

tape.
90 -

The predominant feature of the crystalline orientation characteristics in

this tape is the cy lindrically symmetrical orientation of crystallites about the

T-axis of the tape with the c-axis (and hence the chain molecules) in the crystallites oriented preferentially parallel to T. In addition, a relatively minor population of crystallites in which the a-axis in the crystallites is oriented preferentially parallel to T, is also present in the tape. In short, the c-axis

orientation and the a-axis orientation , which were mentioned in Section 2.2.2

(see also Fig. 9) as occuring simultaneously in certain circumstances in uniaxially

stretched polypropylene, also occur in this tape. The important feature to note

in the case of this tape, however, is that the c-axis and the a-axis orientations

of the two populations of crystallites are respectively oriented parallel preferentially to the transverse direction T in the tape and not parallel to M. This indicates that the film from which this tape was slit was stretched predominantly

in the transverse direction T.

The first aspect to note in Fig. 13 is that the M-axis (Fig. 13a) and the

N-axis (Fig. 13c) WAXD patterns are similar to one another. Furthermore, consideration of the calculated WAXD pattern in Fig. 9a indicates that preferential c-axis

orientation (and hence preferential stretching) parallel to T in the tape would

result in the occurrence of 110, 040, and 130 arcs situated along N and M in M-axis

and N-axis WAXD patterns respectively. This is indeed found to be the case in the

corresponding patterns in Fig. 13a and 13c. Further, reference to Fig. 9a indicates

that 111, 041 and 131 arcs would be expected to occur along diameters at + 40° to

the axis along which the 110, 040, and 130 arcs are situated. This is found to be

so in both Fig. 13a and Fig. 13c, and confirms the occurrence among the crystallites

of preferential c-axis orientation parallel to T.
91 -

The evidence for crystallites having preferential a-axis orientation parallel

to T in this tape is by comparison very weak and limited to the occurrence of two

faint and overlapping (110) arcs which straddle the T-axis in the M-axis and N-axis

diffraction patterns. Such arcs are faintly perceptible in Figs. 13a and 13c, they

could, however, be discerned more clearly in the original x-ray films.

A small angle x-ray diffraction pattern taken with the x-ray beam parallel to

O N is shown in Fig. 13d. Two diffraction spots corresponding to a spacing of 280 A

can be seen situated along T. This pattern indicates in itself the occurrence in

the tape of chain-folded crystallites which are oriented with their fold surfaces

perpendicular to T, and hence with the c-axis and the chain molecules parallel to

T, which features are consistent with the WAXD observations, and thus provide further

confirmation that the predominant orientation among the crystallites in this tape

is preferential c-axis orientation parallel to T.

The density of a sample of this tape was found to be 0.908^ which corresponds

to a weight fraction crystallinity of 0.69.

2. 2. 2d Polypropy lene-E

The M-axis, T-axis and N-axis WAXD patterns obtained from this tape are shown

in Fig. 14. These patterns can be indexed according to the a-monoclinic unit cell

of polypropylene. An examination of these patterns leads to the conclusion that

there apparently exist in this tape four distinguishable populations of crystallites

having different preferred orientations namely, (040) planar orientation , (110)

planar orientation , c-axis orientation parallel to T, and a-axis orientation also

parallel to T. In short, the two orientations identified in the Polypropylene-A

tape and the two identified in the Polypropy lene-D tape occur collectively in this

tape. We shall not attempt to discuss the patterns or the complexities involved
92

Figure

14:

(a)

M-axis,

(b)

T-axis,

and

(c)

N-axis

,

WAXD

patterns

from

the

Polypropy

lene-E

tape.

The

spotty

outer

ring

in

each

pattern

is

the

111

ring

from

poly

crystalline

Si

used

for

calibrating

the

specimen

to

film

distance

which

is

not

the

same

in

all

threediagrams.
- 93 -

in their analysis. We will limit ourselves to pointing out that the simultaneous

existence of these four orientations in the same tape results in the occurrence,

in the WAXD patterns, of several complicating coincidences and overlaps between

arcs corresponding to particular crystallographic planes (e.g., (110) or (040))

in the crystallites of the differently oriented populations. These complications

can be judged, in part for example, from a consideration of the superposition of

the calculated patterns shown in Fig. 9 and those in Fig. 10 when appropriately

oriented relative to one another. The resulting complications and ambiguities

were taken into account in deducing the presence of the four preferred orientations

indicated above. The occurrence of crystallites exhibiting preferred c-axis orientation parallel to T indicates that the film was stretched to a greater extent parallel

to T than to M in manufacture. The density of a sample of this tape was found to be

0.909^ which corresponds to a weight fraction crystallinity of 0.69.

2.2.3 Nylon-11 (Nylon 11-A)

Two different triclinic (see Glossary) unit cells have been proposed for

(21 22 ) Nylon- 11 *

. As background for our observations on the Nylon-11 tape it is of

( 22 ) interest to note that according to Slichter the side by side packing of the

chain molecules and their arrangement in hydrogen bonded sheets in the Nylon-11

crystal lattice is similar to that found in the well established a-triclinic unit

(23) cells of Nylon 6.6 and Nylon 6.10 . The Nylon-11 unit cell parameters given by

Slichter are a = 4.9A, b = 5.4A, c = 14. 9A, a = 49°, 3 = 77°, y = 63°. One chain

passes through this cell with its long axis parallel to the c-axis. These unit

cell parameters are identical with those of Nylon 6.6 and Nylon 6.10 except that the

c-axis is shorter in accordance with the difference in length between the co-amino

undecanoic acid repeat unit in Nylon-11 and the diamine-dioic acid repeat units in
- 94 -

Nylon 6.6 and Nylon 6.10. As is the case for the latter two polymers, one would

expect WAXD patterns of unoriented crystalline Nylon-11 to exhibit in particular,

two characteristic intense rings, one of which corresponds to diffraction from the

(100) planes and the other, which is a composite ring, corresponds to diffraction

from the (010) and (110) planes in the crystallites. The calculated interplanar

O o o spacings are d.^ = 4.36A, d.^ = 3. 7A and d^^ = 3.67A. It is pertinent to note

in anticipation of what follows that the (100), (010) and (110) spacings (which

define the lateral packing of the chains) are known to vary in the case of Nylon 6.6

(24-27) and Nylon 6.10, according to the degree of crystallinity of the polymers

Thus, in rapidly quenched samples which have very low crystallinity, a single broad

diffraction ring replaces the two above mentioned rings. Upon annealing such samples

at elevated temperatures the broad ring resolves itself into two rings whose corresponding spacings approach the (100) and (010) CH0) interplanar spacings in the atriclinic cell as the annealing temperature and hence the crystallinity is increased.

The WAXD patterns obtained from the Nylon-11 tape showed no indication of

crystalline orientation. In fact, as shown in Fig. 15a which was taken with the x-ray

beam parallel to N, they exhibited a broad diffraction ring corresponding to a spacing

O of 4.14A. Based on the previous experience with Nylon 6.6 and Nylon 6.10 summarized

above, this feature was taken as evidence of the prevalence of poor crystalline order

(crystallinity) in the tape. The conclusion was confirmed by the fact that a WAXD

pattern obtained from the tape after it was annealed at 433 K for two hours, exhibited

two distinct rings as may be seen in Fig. 15b. The spacings corresponding to these

O O rings are 4.37A and 3.86A. In view of the fact that Nylon-11 is currently not being

considered as a prime candidate for use in the super conducing cable we have discontinued

work on this tape and Nylon-11 generally for the present. The apparent existence of

(21 22 ) two crystal forms of Nylon- 11 5 is an aspect which needs to be examined further

in any future work on tapes of this polymer.
95

mrH

<UUo

bQ

•H

(a)

N-axis

WAXD

pattern

from

the

Nylon11-A

tape.

(b)

N-axis

WAXD

pattern

from

the

same

tape

after

annealing

at

433 K

for

two

hours.

The

spotty

outer

ring

in

each

pattern

is

the

111

ring

from

polycrystalline

Si

used

for

calibrating

the

specimen

to

film

distance.
- 96 -

2.2.4 Polycarbonate Tapes

Two types of tapes made from poly (4, 4’-dioxydipheny 1-2, 2*-propane carbonate)

were examined, namely Polycarbonate-A and Polycarbonate-B. Both tapes were dyed

in manufacture. The polymer will be referred to below simply as polycarbonate.

(28) According to Bonart v this polycarbonate has a monoclinic unit cell. Its

parameters are a = 12. 3A, b = 10. 1A, c = 20. 8A, y

= 84°. Four chains pass through

the cell with the chain axes parallel to the c-axis.

As an aid to the ensuing discussion of the WAXD patterns obtained from the

tapes we show in Fig. 16 the calculated dispositions of some of the more intense

reflections expected in a WAXD pattern from a polycarbonate film in which the

crystallites are oriented with the c-axis parallel to the machine direction M,

their orientations being otherwise randomized in a cy lindrically symmetrical manner

about M. The reflections which are shown correspond to some of the most intense

ones observed experimentally by Bonart in uniaxially stretched samples, in which

case the most intense ones were the 020 and the 202 reflections. In keeping with

the nomenclature used for polypropylene, the type of orientation depicted in Fig. 16

will be referred to as c-axis orientation parallel to M.

2.2.4a Polycarbonate-A

The M-axis, T-axis and N-axis WAXD patterns obtained from this tape are shown

in Figs. 17a, b, and c respectively.

The WAXD pattern obtained with the x-ray beam parallel to N (Fig. 17c) exhibited

arcs which could be indexed 101, 103, 202, 203, 213, and 303 based on their corresponding interplanar spacings. Furthermore, a comparison of the dispositions of these

arcs relative to the M-axis in the diffraction pattern, with the dispositions of the

same reflections in the calculated pattern illustrated in Fig. 16 showed that they

were indeed similar to one another. Particularly conspicuous features were the

occurrence of the 101, 202, and 303 arcs along diameters oriented at very close
- 97 -

co

t

Q 01

O

CO 4J •H

&

u i—

•H £4 cO

cO 0) S

JO 5-4

c 03 4-1

O

ai

O

c

•u

CO

G OJ CO

c a) 5-4 •H o •H cO •H 5-i g

4-1

O CO CO CJ C cu

a) CU

O J3 i—i 5-i *H

4-1 cO 4-J

QJ cO

G

5-i CO 4-J 5-4 ai c 1 CO 4J 0) >0 O •H •H co t—H !-i r-l O «

#5 CO

c

co 4-J 5-4

o i—l CO •H •H CM &

0) JO

4-1 a

a 4-J a; co S-i o ai •rl CM -C e 43 P cO

<•«

G 4-J

O MlG

CM • cO JO O c •r4 4-J o 43

P\ •H 4-J CM 4-J 0) 3 O CO JO O

CM 4-1 4-J JO c G

«N OJ

G

T“H •r-l •H

C

oG

O

CM

O

c •H o JO

«s CO •H CO CO •H 4-1 G o X U 4-4 pH CO a) 1 5-4 i—

«s

a •r-tG

CM 43O

O Ml •H i—

G i—

G

•H cO 4-J

VO

a)

5-i 3

Ml H

pti
Figure

17:

(a)

M-axis,

(b)

T-axis,

(c)

N-axis,

WAXD

patterns

from

Polycarbonate-A

tape.

Contact

prints

of

originals,

specimen

to

film

distances

are

not

identical.

The

strong

arcs

situated

along

N

in

(a)

and

(b)

are

020

reflections.

In

(c)

the

most

intense

arcs

situated

along

diameters

at

about

+

60°

to M

are

202

reflections.

(d)

N-axis

SAXD

pattern

from

the

same

tape.
99

to + 60° relative to M, and that the 202 arcs were the most intense - they are the

most prominent ones in Fig. 17c. The other arcs were considerably fainter and are

somewhat difficult to distinguish in Fig. 17c, in particular the 101 arcs which are

overshadowed by the scattering around the central beam stop. All these weaker reflections were however discernable in the original photographic film.

The above mentioned coincidence between the calculated dispositions of the 101,

202, 303, 103, 203, and 213 reflections and the experimentally observed ones in the

N-axis diffraction pattern, leads to the conclusion that the crystallites in the

tape are oriented with the c-axis preferentially parallel to M. There is, however,

a feature which is conspicuous by its absence in the experimental N-axis WAXD pattern

(Fig. 17c), namely the absence of 020 arcs. As may be seen from Fig. 16, 020 reflections would have been expected to occur along T in Fig. 17c, and would also have been

expected to be as intense as the 202 reflections, if the preferred orientations of

the crystallites in the tape corresponded to the cy lindrically symmetrical c-axis

orientation parallel to M represented in Fig. 16. In short, the absence of 020

reflections along T in the N-axis WAXD pattern, taken together with the evidence

obtained from the same pattern which indicates that the crystallites are oriented

with their c-axis preferentially parallel to M, suggest the manifestation of some

preferential orientation of the (020) planes relative to the surface (i.e., the MT

plane) of the tape. This is substantiated by the WAXD pattern obtained with the

x-ray beam parallel to M (Fig. 17a) in which the most prominent diagnostic feature

is the occurrence of intense 020 arcs along N indicating that the (020) planes in

the crystallies tend to be preferentially oriented parallel to the plane MT of the

tape. It may also be noted that the T-axis WAXD pattern (Fig. 17b) exhibits 020

arcs along N, and is also characterized by the absence of 101, 202, and 303 reflections along diameters at + 60° to M. Both of these features are consistent with

the deductions summarized above.
100 -

A SAXD pattern taken with the x-ray beam parallel to N is shown in Fig. 17d.

It exhibits distinguishable if diffuse diffraction spots situated along M and

O corresponding to a periodic spacing of about 170A. These features point to the

occurrence of chain folding in the crystallites, to the orientation of the fold

surfaces at right angles to M, and to the orientation of the c-axis in the crystallites preferentially parallel to M. This latter aspect is in agreement with the

WAXD results concerning the orientation of the c-axis of the crystallites.

In summary, the WAXD diffraction patterns obtained from this tape indicate

that the crystallites are oriented with their c-axis (and hence their constituent

chains) preferentially parallel to M, and that the (020) planes in the crystallites

tend to be preferentially oriented parallel to the plane (MT) of the tape. The

SAXD data which point to the manifestation of chain folding in the crystallites,

substantiate the orientation of the c-axis in them preferentially parallel to M.

2.2.4b Polycarbonate-B

The WAXD patterns obtained from this tape exhibited no distinguishable crystalline orientation. Indeed, as illustrated in Fig. 18a which is a pattern obtained

with the x-ray beam parallel to N, the patterns were characterized by the occurrence

of a diffuse halo indicative of poor crystalline order and hence very low crystalO Unity. The spacing corresponding to this halo is about 5.3A. After annealing the

tape at 473 K for twenty hours a sharper diffraction pattern indicating increased

crystallinity was obtained. Such a pattern is illustrated in Fig. 18b in which the

O inner and most intense ring corresponds to a spacing of 5.08A, which agrees closely

O with the (020) interplanar spacing, of 5.02A, calculated on the basis of Bonart’s

-unit cell parameters'1 . We have not investigated the effects of annealing this

tape at higher temperatures on WAXD patterns in order to characterize the changes

in the patterns as a function of crystallinity. It was considered sufficient, for

the purpose of the present survey, and for qualitative comparison with the Polycarbonate-A tape, to have established the poor crystallinity and the lack of detectable

crystalline orientation evidenced by the WAXD patterns of the Polycarbonate-B tape.
101

-O

Figure

18:

(a)

N-axis

WAXD

pattern

from

the

Polycarbonate-B

tape.

(b)

N-axis

WAXD

pattern

from

the

same

tape

after

annealing

at

473

K

for

twenty

hours.

Contact

prints,

specimen

to

film

distances

not

the

same.

See

text

for

comparison

of

patterns.
102 -

2.2. 5 Polyethylene Tapes

We report below some observations on the characteristics of crystalline

orientation in the Polyethylene-A and the Polyethy lene-D.

As background to the observations described below it may be first pointed

out that the unit cell of polyethylene is orthorhombic (see Glossary) . The unit

cell parameters as determined by Bunn are a=7.4oA., b=4.93A, c= 2 . 534&^^. Two

chains pass through the unit cell and are parallel to the c-axis. Apart from the

usual manifestation of preferential c-axis orientation (same nomenclature as used

for polypropylene and polycarbonate) parallel to the stretching direction in the

case of uniaxially stretched samples, a variety of preferred types of orientation

have been achieved in polyethylene films or sheets by, for example, subjecting

them to biaxial stretching rolling followed by heat relaxation or combina-

(32) tions of uniaxial stretching, rolling, and annealing

2.2.5a Polyethylene-A

WAXD patterns taken with the x-ray beam parallel or very close parallel to

M, T and N are shown in Figs. 19a, b, and c, respectively.

The fact that the N-axis diffraction pattern (Fig. 19c) was ringed in character,

coupled with the fact that the positions of the diffraction arcs in the M-axis

(Fig. 19a) and T-axis (Fig. 19b) patterns were essentially similar to one another,

suggested at the outset the occurrence of a preferred crystalline orientation, or

of preferred crystalline orientations, which are cylindrically symmetricaly about N.

This indication, coupled with the occurrence of (200) and (110) arcs along N in both

the M-axis and the T-axis diffraction patterns suggested in turn the existence of

two populations of crystallites in the tape, having preferential (200) planar

orientation and {110} planar orientations respectively (same nomenclature as for

polypropylene Section 2.2.2). Such orientations have been previously reported

by Adams .
Figure

19:

(a)

M-axis

,

(b)

T-axis,

(c)

N-axis

,

WAXD

patterns

from

the

Polyethy

lene-A

tape.

The

spotty

ring

in

(c)

is

the

111

ring

from

poly

crystalline

Si

used

for

calibrating

the

specimen

to

film

distance.

The

intense

inner

arc

situated

along

N

in

(a)

and

(b)

is

a

110

reflection.

The

inner

ring

in

(c)

is

a

110

ring.
104 -

A comparison was made between the experimental M-axis and T-axis WAXD

patterns and the pattern shown in Fig. 20 which represents the dispositions of

the 110, 200, 210, and 020 reflections in an M or T axis WAXD pattern of a

hypothetical tape in which one population of crystallites exhibits (200) planar

orientation and the other population exhibits {110} planar orientation . It

should be emphasized in this connection that the angular spreads of the arcs in

the experimental WAXD patterns in Figs. 19a, and 19b, are large. This feature,

coupled with uncertainties involved in estimating the positions of maximum intensity along the arcs, has made it difficult to analyze and compare these patterns

rigorously with the calculated composite pattern in Fig. 20. We shall not enumerate

or discuss these difficulties. We point out that the incidence in the experimental

M-axis and T-axis diffraction patterns, of 200 arcs along N, of 110 arcs along

diameters at about + 56° relative to N, and of 020 arcs along T and M respectively,

are consistent with the occurrence of a population of crystallites having preferential

(200) planar orientation in the tape. Furthermore, the occurrence of 110 arcs along

N and the manifestation of distinguishable 200 arcs along diameters at + 50° to 55°

relative to N, and (020) arcs along diameters at about + 30° to N are indicative of

the occurrence of preferential {110} planar orientation .

Additional WAXD experiments involving the recording of diffraction patterns

with the x-ray beam tilted systematically at different angles relative to the M,

N, and T axes should shed further light on the crystallographic orientations in

this tape. The main features which we derive from the present WAXD experiments are

that the c-axis and hence the chain molecules in the crystallites are oriented preferentially parallel to the plane (MT) of the tape and that the WAXD patterns do

not reveal any preferential orientation of the c-axis about any direction in that
[oh] - 105 - gGgI—

>> Xug

4HO

44 01g

oo

G

H fi

H

00C a) 3 § c -H o a a

CO

H

o

g

ft

o •ft

a ftG

a. gj

o

X

G Ph

o 4-t

G

Oa1 CO

o

G CO

G

G 44 •H G X o

ft 4-4 iH rH

G ft 4-1

G

G

c

O

o CJ rH

ft

G

O 4-t

G i—

G rH i—

G

4-1 CL, CO

t

—4H ft

4-4

C

GG

G

G Eh

o rH ft

a CU •ft rH

4-t

G

G CO

QG

O ft

X

G

rGG

G

G

4-1 < U i—

CU

G

S 4h

G rH

G

o

G CO ft

a 4-J ft G G G r-*-\

G rH

G

G CO

o •H G X rH G .—

rH 4-1

a rH

t

—

A rH U '-r-' CO G G /-N ft G ft ft o •rH ft O G G o O •H •H CU CM G

4-1 CO V—' H3)

X

a

G

G CU 4-1

G

O rH ft rH

mhg

ft oCMo

T3

•H

44OG

ft •HG

CO

ftO

•rl<U X44

0)>

CL. CO O X

<D -CH

0)>

CO -C

CO

CD

4-1 •ft

(D X!H

CO

CD

4-1

O « H

CM

9\ - g o

ItHO

rH 44 o

rH

CD X4J

COCo

•H

4-1 G

4-t G

CD •H

ftOO&

CU 4-4 * i—

GG

ftG

G

4-4 COaG

00 -G

a

c

w

G

-GG

4-1 CO

o

4-4

COG

-G

•U

O

X -ft 00 X t *

4-4 -S G

00

o

Lft

S 00

G

G -ft

OG

C -ft •H 44

G -H

GG

fl

X

&GX 44

o

o

o

G

•rH >> i1 •rH CO

G

44

G rH 44 •H -H

•H ft

OG

X ft

CO 1 <44 44

G

O OX G 1 a g g G ft CO G X -iH G

•H

X 44 ft

G

G

G 44

o

X

g

00 44 i—

X x G ft a G

4-1 G

rH3Oi—

GU

4-4 -H>G

-G

GG

'G

S

rH

O

•H

4-4 CM

rH

O •ft i—

GX4-4

o

4-4

00

4-4 X00

•H

ft

4JG

COGXGGO

•H

4-t

4-1 GGOO

fta

•HaG

ft G

rC

4-t

T3 ° S 4-4 G

O

CMG

ft3

oo •H

fn
106 -

plane. A SAXD pattern obtained with the x-ray beam parallel to N is shown in

Fig. 19d. It exhibits a very diffuse diffraction ring which, in addition to

indicating the presence of chain-folding in the constituent crystallites in the

tape, also points to the absence of (or very poor) preferential orientation of

the chain molecules in the crystallites relative to M. The spacing corresponding

O to the diffraction ring in Fig. 19d is - 200A. Finally, the density of a sample

of this tape was 0.932 which corresponds to a weight fraction crystallinity of

0.57.

2.2.5b P o lye thy lene

M-axis , T-axis and N-axis WAXD patterns obtained from this tape are shown in

Figs. 21a, b, and c. The N-axis WAXD pattern is characterized by the incidence

of 110, 200, and 020 arcs along diameters oriented at close to + 45° relative to

M. These features indicate that the crystallites in this laminated tape, which

Consists of two layers of film, are oriented with their c-axis preferentially at

either + 45° or -45° relative to M. This is consistent with a description of how

this tape is constructed from its constituent two layers of film. It may be concluded that in one layer the crystallites are oriented with their c-axis preferentially in the (MT) plane and preferentially at + 45° relative to M but with their

orientation otherwise randomized about the +45° direction, whereas in the other

layer they are oriented with their c-axis preferentially parallel to the -45°

directio and randomized about that direction.

A SAXD pattern obtained with the x-ray beam parallel to N is shown in Fig. 21d.

No discrete reflections were observed. The continuous scatter around the beam stop

is almost square-like in appearance with the corners of the squares situated at + 45°

to M. This feature can be interpreted as indicating the presence of elongated microvoids oriented with their long dimension at + 45° to M. The manifestation of fourfold symmetry in the scatter around the beam stop is consistent with the two preferred

orientations indicated above.
107

Figure

21:

(a)

M-axis,

(b)

T-axis,

and

(c)

N-axis

WAXD

patterns

from

the

Polyethy

lene-D

tape.

The

spotty

ring

in

each

pattern

is

the

111

ring

from

poly

crystalline

Si

used

for

calibrating

the

specimen

to

film

distance.

(d)

N-axis

SAXD

pattern

from

the

same

tape.
-108 -

2.2. 6 Discussion and Summary

Using primarily WAXD as a probe and SAXD as an ancillary tool, a qualitative

survey has been carried out of the crystalline orientation in the following tapes:

Polypropylene (A,B,C,D,E), Nylon 11 , (Nylon 11- A) . Polycarbonate (A,B), Polyethylene (A,D) .

It has been pointed out in Sections (1.3.2), (1.3.4) and (1.3.5) that the

Nylon 11, the polyethylene, and the polypropylene tapes meet the established

riteria in so far as their dielectric properties in the range 6-8 K are concerned.

They are considered unsuitable however with regard to at least one aspect of

(33) their mechanical properties . This aspect is considered below in conjunction

with our observations on the structural characteristics of these tapes.

The matter of what are the desirable mechanical properties which polymer tapes

must have is a complex problem which remains to be fully resolved in so far as

establishing comprehensive criteria. Among the factors which are to be considered

are the tensile modulus, the yield stress, the elongation to break, the breaking

strength, creep and stress relaxation, and non-linear viscoelastic characteristics.

These properties which are structure dependent, and which are interelated, are of

interest not only at cryogenic temperatures, but also at room temperature. The

interest in this latter case is in connection with the tape winding process used

in the manufacture of the superconducting cables. The current view is that the

tensile modulus E of the tapes at room temperature and in the machine direction M

5 5 (33) should be 5 x 10 - 6 x 10 psi (3.4 - 4.1 GPa) or greater , as determined under

(34) testing conditions adopted at BNL . In addition the compressibility of the tapes

is a factor whose importance to the success of the tape winding operation is currently receiving much attention.
109

Confining our remarks to the tensile modulus E (parallel to M-axis) of the

tapes at room temperature, it is important to bear in mind at the outset that

there are limitations to using the magnitude of E obtained under one set of testing conditions as a general performance criterion. Not withstanding these limita-

(35) tions which have been outlined in a recent communication and will not be

(34) repeated here, data on E derived from a single set of testing conditions

(specimens 12,7 cm long, 1.9 cm wide, cross-head speed 1.27 cm/min. temp. 293 K)

provide a basis for comparison relative to the tentative criterion of E = 5 x 10^ -

6 x 10^ psi (3.4 - 4.1 GPa).

The tensile properties of the tapes which have been measured at BNL are listed

in Table Vila, from which it can be seen that the tensile moduli of the polypropylene

,

the Nylon 11 , and the polyethylene tapes fall short of the above mentioned criterion.

The respective structural characteristics of these tapes are certainly not favorable

in this connection. It is sufficient in the present context to point out that

among the features necessary for achieving a high tensile modulus are a high crystallinity, and the orientation of the crystalline regions (crystallites) with their

c-axis (i.e. the chain molecules) parallel to the straining direction which is M

in the case of the tapes. The better the alignment of the c-axis in the crystallites

parallel to that direction, the higher the tensile modulus. The polypropylene, the

Nylon-11 and the polyethylene tapes fall short with respect to either one and/or the

other of these features as can be judged from the summary given in Table Vllb of

the qualitative WAXD results described in Sections (2.2.2) to 2.2.5). Finding

commercial films, or alternatively, producing special films or tapes which have

been subjected to high draw ratios in the machine direction M during manufacture

is clearly necessary if the criterion for E is to be met. A factor to bear in

mind in this connection, however, is the tendency for samples having ultra-high

c-axis orientation to fibrillate.
no -

In the case of the polycarbonate tapes, it has been pointed out in Section

(1.3.1) that at 30 K and below the dielectric loss behavior of the Polycarbonate-A

and the Polycarbonate-B are identical to one another (see Fig. 3) and do not meet

the required specifications at the superconducting cable operating temperatures,

6-8 K. In view of the evident fine structural differences between these two tapes

as revealed by their WAXD characteristics and as summarized in Table Vllb (see also

Sections 2.2.4a and 2.2.4b), it appears that this polymer is intrinsically unsuitable in so far as its dielectric properties are concerned. It may be noted that

the structual differences between the two tapes are reflected in the distinct

difference in intensity between their respective loss peaks at circa 180 K. Furthermore, as would be expected, the tensile modulus of the crystalline and oriented

Polycarbonate-A is higher than that of the poorly crystalline Polycarbonate-B (see

TAble VII). Indeed, of the various tapes listed in Table VII, the Polycarbonate-A

satisfies most closely the criterion for E, its use in the cables is negated, however, due to its dielectric properties.

Finally, although, as we have pointed out above, the polypropylene and the

polyethylene tapes meet the required dielectric performance criteria at the superconducting cable operating temperatures, 6-8 K, differences between dielectric loss

levels were observed among tapes of each of these polymers in the range 4-10 K.

The origins of these differences remain obscure. It is at present not clear whether

these differences are caused wholly due to differences in additive content or

whether structural features are a contributing factor.

2.3. Some Observations on the Surface Textures of Polymer Tapes

Following some background remarks, we illustrate below a few initial observations

on the surface textures of some polymer tapes. These observations point to the fact

that opposite surfaces of some tapes exhibit different textural features on a coarse

scale. In addition some of the examples which will be shown serve to illustrate

diverse surface textural features encountered in different tapes.
Ill -

The long term objective of the study of the surface textures of promising

or trial polymer tapes is to characterize them at different levels of resolution.

The techniques which will be used include the application of optical microscopy

and electron microscopy to examine replicas of the tape surfaces, and the application of scanning electron microscopy to examine the surfaces directly. The

reason for undertaking such studies stems from interest at BNL in the following

tape properties which are being investigated both at BNL and elsewhere, namely:

(a) The frictional properties of the tapes, which are of interest in connection

with the desired flexibility which the superconducting cables must have so that

they can be wound around 8-10 ft. diameter reels for transportation to installation

sites. (b) The radial thermal conductivity at cryogenic temperatures of the

(~ 0.5-1") thick layer of polymer tape insulation in the cables. This is of interest in connection with the problem of the dissipation of heat generated in

the insulation due to dielectric loss. Knowledge of the nature of the interfacial

contact between successive tape layers, and hence knowledge of the surface textures

of the tapes is clearly relevant to both (a) and (b).

Our current observations on the surfaces of the tapes are presented below in

the form of short notes.

2.3.1 A coarse textural difference between opposite surfaces of the

Polypropylene-A Tape

(3 Fig. 22a and Fig. 22b are phase contrast light optical micrographs of replicas

of opposite surfaces of this tape. The particular features we wish to point out are

the somewhat irregular, but roughly circular or oblong, outlines in the central part

of Fig. 22a (see arrows) where three such features may be seen. These features were

observed throughout this particular surface of the tape. The diameters of the

circumscribed areas varied, the largest being ~ 120 pm. No similar features were

observed in replicas of the opposite surface of the tape as may be judged from

Fig. 22b.
112

Figure

22

:(a)Replica

of

one

of

the

surfaces

of

the

Poly

propyleneA

tape.

(b)

Replica

of

the

opposite

surface

of

the

same

tape.

Phase

contrast

light

optical

micrographs.

(c)

Scanning

electron

micrograph

of

the

same

surface

of

the

tape

as

that

which

exhibits

the

features

shown

in

(a).
- 113 -

Fig. 22c is a scanning electron micrograph taken of a portion of the same

(37) tape surface as that whose replicas exhibit the type of features seen in

Fig. 22a. It can be seen from Fig. 22c that the features observed in the replicas

correspond to the occurrence of ridges which protrude from that tape surface. Detailed knowledge of the production procedures used in the manufacture of this film

would shed some light on the origins of these ridges and their occurrence on only

one side of the film. We point out parenthetically that examination of replicas

of the Polypropy lene-B tape under the optical microscope revealed the occurrence

of similar ridges on only one side of that tape. No such ridges were observed in

replicas of the Polypropylene-D or the Polypropylene-E tapes.

2.3.2 Texture differences between opposite surface of the Poly carbonate-A tape .

Fig. 23a and Fig. 23b are phase contrast light optical micrographs of replicas

of opposite surfaces of this tape. The main feature we wish to point out in this

case is the apparently cellular appearance of the area shown in Fig. 23a in which

oblong outlines (see arrow) which are elongated in the direction parallel to M can

be seen. These bright outlines correspond to a difference in height at the surface

of the tape relative to the surroundings. These features occur throughout this

surface of the tape. They are absent, however, in replicas of the opposite surface

as may be judged from Fig. 23b. Whether the outlines seen in Fig. 23a correspond

to pronounced ridges at this surface of the tape remains to be determined.

It is also of interest to note the occurrence in Fig. 23b of lines which transverse the area shown in a variety of directions. Such lines which correspond to

a difference in height relative to the surrounding area of the tape surface were

seen in several replicas of this surface. No similar profusion of such lines was

observed in replicas of the other surface as may be judged from Fig. 23a.
- 114 -

O

Figure

23:

(a)

Replica

of

one

of

the

surfaces

of

the

Polycarbonate-A

tape.

(b)

Replica

of

the

opposite

surface

of

the

same

tape.

Phase

contrast

light

optical

micrographs.
115 -

2.3.3 Texture differences between opposite surface of the Polyethylene- A tape .

In this particular case differences between the opposite surfaces of the tape

could be resolved under the phase contrast light optical microscope by focussing

it on the opposite surfaces of the tape itself. Focussing on one particular

surface always revealed a profusion of tree-branch like features exhibiting different configurations and extents of branching as may be seen in Fig. 24a (see

arrows). Fig. 24b represents the same area of the tape as that shown in Fig. 24a,

but with focussing on the opposite surface. The tree-branch like features seen

in Fig. 24a are clearly out of focus in Fig. 24b in which a profusion of faint

narrow lines running parallel to M can be seen.

2.3.4 Summary and Comment

The main feature of the observations described in the previous Sections

(2. 3. 1-2. 3 . 3) on the surface textures of some of the polymer tapes is the manifestation of differences between opposite surfaces of those tapes. The differences

which were pointed out may be described as being coarse in that they are readily

detected at relatively low magnifications (e.g. x 160) in the light optical microscope using phase contrast optics. The term coarse, however, applies to the

lateral extent of the features, their topographical characteristics remain to be

examined in detail using scanning electron microscopy and the examination of

surface replicas in the transmission electron microscope. This latter technique

will also shed light on the finer aspects of the textures of the tape surfaces.
116

O

Figure

24:

Phase

contrast

light

optical

micrographs

of

the

same

region

in

the

Polyethy

lene-A

tape.

(a)

Microscope

focussed

on

upper

surface

of

the

tape.

(b)

Microscope

focussed

on

lower

surface

of

the

tape.
117 -

References

1. G. P. Nance and F. A. Sliemers, Summary Report to Brookhaven National

Laboratory, Battelle Columbus Laboratories, Feb. 13, 1976.

2. A. Muller, Private Communication.

3. R. A. Thomas and C. N. King, Appl. Phys. Lett. 406 (1975).

W. A. Phillips, Proc. Roy. Soc. London, A 319 , 565 (1970).

4.

J. M. Crissman, J. A. Sauer, and A. E. Woodward, J: Polymer Sci. A _3,

5075 (1964)

5

.

The crystallization and fine structure (morphology) of crystalline polymers

is discussed in the following two books: (a.) P. H. Geil, "Polymer Single

Crystals", Interscience Publishers, N. Y. (1963); (b) B. Wunderlich,

"Macromolecular Physics", Vol. I (1973), Vol. II (1976), Academic Press, N. Y.

For shorter reviews on the morphology of crystalline polymers see: (c) A.

Keller, Reports on Progress in Physics 31 , Part 2, 623 (1968). (d^) F. Khoury

and E. Passaglia in, "Treatise on Solid State Chemistry", Vol. 3, Chapt. 6,

Plenum Press (1976) . For models depicting crystalline orientation, chain

folding, and tie molecules in uniaxially stretched polymers see: (e) R.

Hoseman, Crit. Revs. Macromol. S.ci. 1 (No. 3), 351 (1972). (f) A. Peterlin,

J. Matls. Sci. j>, 490 (1971). (jg) A. Peterlin, Text. Res. J. , 42:, 20 (1972).

6 . Relationships between the fine structure and the physical properties of polymers

are discussed in the following books: (a) N. G. McCrum, B. E. Read, G.

Williams, "Anelastic and Dielectric Effects in Polymeric Solids", Wiley (1967);

(b) I. M. Ward, "Mechanical Properties of Solid Polymers", Wiley 1971.

Relationships between the fine structure of stretched samples, their mechanical

properties, and the extent of stretching (draw ratio) have been reviewed by

(c) D. M. Biggs, Battelle Columbus Laboratories Summary Report to BNL,

Dec. 2nd (1975) . Basic discussions on the elastic moduli of polymers may be

found in the following papers: (d) I. Sakurada and K. Kaji, J. Polymer Sci.

Part C 31 , 57 (1970); (e) L. Holliday and J. W. White, Pure and Appl. Chem.

26 , 545 (1971); (f) I. Sakurada and K. Kaji, Makromol. Chem. Suppl. _1

,

599 (1975).

7. G. Natta and P. Corradini, Nuovo Cimento JJ5, (Suppl. No. 1), 40 (1960).

8. See for example International Tables for X-ray Crystallography. Volume II,

p. 177 (Kynoch Press, 1959).

9 .

10 .

11 .

12 .

13 .

P. G. Andersen and S. M. Carr. J. Matls. Sci. ^0, 870 (1975).

E. S. Clark and J. E. Spruiell, Polymer Preprints ll5, (No. 2),

F. Khoury, J. Res. Natl. Bur. Stand. 70A , 29 (1966).

F. J. Padden and H. D. Keith, J. Appl. Phys. J37, 4013 (1966).

F. J. Padden and H. D. Keith, J. Appl. Phys. _44, 1217 (1973).

S. Okajima, K. Homraa, J. Appl. Polymer Sci. 12^, 411 (1968).

343 (1975).

14 .
118 -

15. M. Kawai, Proceedings of the Fifth International Congress on Rheology Vol. 1,

p. 97 (S. Onogi Edit., University Park Press, Baltimore, 1969).

16. M. Wejo and S. Hoshino, J. Appl. Polymer Sci. ^4, 317 (1970).

17. G. C. Adams, Structure and Properties of Polymer Films, Polymer Science

and Technology, Vol. 1, p. 169 (R. W. Lenz and R. S. Stein Edits., Plenum

Press, N. Y. 1973)

18. Z. W. Wilshinsky, J. Appl. Polymer Sci. _7, 923 (1963).

19. R. Kitamaru and S. H. Hyon, J. Polym. Sci.: Polymer Phys. Ed. _13, 1085 (1975).

20. G. Natta, M. Peraldo and P. Corradini, Stereoregular Polymers and Stereospecific

Polymerization, Vol. 2. (F. Natla and F. Danusso Eds.) p. 600, Perganon Press,

1967.

21. K. Little, Brit. J. Appl. Phys. 10, 225 (1959).

22. W. P. Slichter, J. Polymer Sci. 36. , 259 (1959).

23. C. W. Bunn and E. V. Garner, Proc. Royal Soc. (London) A189 , 39 (1947).

24. P. F. Dismore and W. 0. Statton, J. Polymer Sci. Part C JL3, 133 (1966).

25. P. G. Stern, Kolloid Z. Z. Polymer, 215 , 140 (1967).

26. M. Starkweather, Jr., J. F. Whitney and D. R. Johnson, J. Polymer Sci. A,

715 (1963).

27. I. Sandeman and A. Keller, J. Polymer Sci., 401 (1956).

28. R. Bonart, Makromol. Chera. 92 , 149 (1966).

29. C. W. Bunn, Trans. Faraday Soc. J15, 482 (1939).

30. G. C. Adams, J. Polymer Sci. Part 2, 9^, 1235 (1971).

31. I. L. May and A. Keller, J. Matls. Sci. _1, 41 (1966).

32. J. J. Point, G. A. Homes, D. Gezovich, and A. Keller, J. Matls. Sci. _4,

908 (1969).

33. A. Muller, private communication.

34. A. Muller, RGE, j?4_, 568 (1975) , paper presented before the 12th Section of

the Societe des Electriciens , des Electroniciens , et des Radio-electriciens

35. Letter from F. Khoury to A. Muller (BNL) , May 21st (1976)
119

36. The replicas are prepared as follows: A drop of a 10% solution of cellulose

nitrate is deposited on the surface which is to be replicated. The solvent

is allowed to evaporate at room temperature leaving behind a dry film of

nitrocellulose whose side in contact with the tape is imprinted with the

details of the topography of the tape surface in reverse. The nitrocellulose

replica is then gently stripped from the tape surface with tweezers and

examined under the phase contrast light optical microscope.

O 37. As is common practice, the tape surface is coated with a thin layer (-200 A)

of evaporated gold prior to examination in the scanning electron microscope

in order to prevent charging.
120 -

Table I

Dielectric Constant and Loss at 100 Hz and 1 kHz

Polycarbonate-A Polycarbonate-B

t = .057 mm t = .060 mm

T e tan 6 x 10^

100 Hz (1 kHz)

e

£ tan 6 x 10

100 Hz (1 kHz)

4.2 2.33 60(61) 2.48 59(61)

6 2.32 63(69) 2.48 63(70)

8 2.32 77(79) 2.48 77(81)

10 2.32 80(89) 2.48 87(92)

30 2.28 160(169) 2.48 158(165)

55 2.49 256(257)

80 2.28 478(438) 2.47 515(441)

100 2.49 1019(819)

120 2.30 1365(1164)

125 2.49 2031(1690)

150 2.51 3161(2927)

175 2.53 3765(3990)

190 2.33 1875(2503)

200 2.55 3443(4300)

225 2.56 2318(3497)

250 2.56 1196(2091)

273. 2.39 938(820) 2.50 443(625)
121 -

Table II

Dielectric Constant and Loss at 100 Hz and 1 kHz

Nylon 11-A Polysulfone-A

t = .040 mm t = .053 mm

T £

tan 6 x 10

100 Hz(l kHz) £

tan 6 x 10

100 Hz (1 kHz)

4.2 2.52 20(23) 2.52 68(71)

6 2.52 16(21) 2.51 80(85)

8 2.52 20(21) 2.50 95(100)

10 2.52 18(20) 2.51 113(110)

30 2.52 30(34) 2.49 207(209)

80 2.52 296(247) 2.49 528(524)

120 2.53 1729(1333) 2.47 712(737)

190 2.67 10590(11750) 2.42 815(822)

273 2.99 20330(19310) 2.41 755(758)
122 -

Table III

Polyethylene-BNL Samples and Treatment History

BNL

No

Antioxidant

Extraction

Solvent

1 As received none

2 As received methanol

3 XX

0.0492%

none

4 XX

0.1024%

none

5 XX

0.1024%

methanol

6 XX

0.1024%

cyclohexane

7 XX

0.258%

none

8 XX

0.5004%

none

9 YY

0.0488%

none

10 YY

0.1086%

none

11 YY

0.1086%

methanol

12 ZZ

0.0492%

none

13 ZZ

0.1028%

methanol

14 ZZ

0.1028%

none
123 -

Table IV

Dielectric Constant and Loss at 100 Hz and 1 kHz Polyethylene

Polyethy lene-A Polyethylene-C Polyethy lene-D P o ly e thy lene- BNL- 2

6

T

t = .026

e

mm

£ tan 6 x 10

100 Hz(lkHz)

t =

e

. 104 mm

tan 6 x 10^

100 Hz (1 kHz)

t =

e

. 102 mm

tan 6 x 10

100 Hz (1 kHz)

t =

e

.170 mm

tan 6 x ! 100 Hz (1

4.2 2.13 5(13) 2.14 12(33) 2.09 6(16) 2.41 6(29)

6 2.12 3(12) 2.14 9(26) 2.09 4(12) 2.41 3(13)

8 2.12 6(9) 2.14 8(21) 2.09 4(10) 2.41 7(4)

10 2.12 5(8) 2.14 5(18) 2.09 6(9) 2.41 5(6)

30 2.12 6(9) 2.14 6(13) 2.09 15(7) 2.41 5(8)

55 2.11 6(9) 2.13 5(10) 2.08 5(8) 2.41 3(5)

80 2.10 13(15) 2.13 12(12) 2.08 10(12) 2.40 4(7)

100 2.09 26(27) 2.12 25(23) 2.07 20(18) 2.40 10(8)

125 2.07 44(41) 2.11 42(46) 2.07 42(37) 2.38 17(16)

150 2.05 71(69) 2.11 90(97) 2.06 80(80) 2.37 27(30)

175 2.03 61(82) 2.10 102(145) 2.05 98(118) 2.36 22(33)

200 2.01 34(44) 2.08 141(140) 2.03 138(121) 2.34 12(10)

225 1.98 32(36) 2.07 187(213) 2.02 202(203) 2.33 6(6)

250 1.96 36(38) 2.06 375(372) 2.01 296(307) 2.31 9(4)

273 1.93 51(52) 2.04 365(459) 1.99 268(331) 2.30 6(7)
BNL

No.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

124 -

Table V

Loss Data Polyethylene-BNL Samples

Tan 6 x 10^ at 100 Hz (1 kHz)

Temperature

4.2 K 5.1 K 6 K 8 K 10 K 30 K

7 4(21) (5(17) 7(8)

6(29) 3(13) 7(4) 5(6) 5(8)

26 11(48) 9(36) 0(16)

16 11(48) 7(35) 4(15)

9 28(18) 7(12) 0(7)

2 0(9) 0(4) 0(4)

88 4(214) 21(165) 0(62)

232(869) 126(636) 73(448) 50(332) 20(129)

25(106) 17(70) 15(47) 9(34) 5(15)

14(79) 5(47) 19(34) 2(23) 2(14)

8(36) 6(13) 2(3) 2(2) 5(1)

14(58) 10(32) 0(19) 0(14) 6(8)

0(46) 0(21) 0(13) 1(6) 3(5)

9(61) 9(32) 5(21) 9(11) 8(5)
T

4.2

6

8

10

30

55

80

100

120

125

150

175

190

200

225

250

273

125

Tab re VI

Dielectric Constant and Loss at 100 Hz and 1 kHz Polypropylene

Polypropylene-A Polypropy lene-B Polypropy lene-C Polypropy lene-D

t = . 027 mm t = .028 mm t = . 134 mm t = .033 mm

£ tan

100

6 x 10^

Hz (1 kHz)

e tan 6 x 10^

100 Hz (1 kHz)

£ tan 6 x 10^

100 Hz (1 kHz)

£ tan 6 x 10^

100 Hz (1 kHz)

2.09 32(98) 2.17 30(91) 2.18 8(10) 1.99 17(19)

2.08 22(71) 2.16 19(65) 2.18 5(10) 1.99 27(22)

2.08 13(53) 2.16 14(48) 2.18 4(9) 2.00 19(18)

2.09 11(44) 2.17 12(40) 2.18 10(10) 1.99 28(18)

2.10 8(29) 2.18 9(27) 2.18 18(17) 1.98 35(23)

2.06 9(12) 2.15 9(12) 2.00 27(23)

2.09 9(10) 2.17 29(24) 1.98 39(34)

2.08 11(13)

2.15 69(73)

1.99 65(48)

2.07 14(17) 1.97 100(95)

2.06 14(19) 1.96 5.9(63)

2.06 20(22)

2.14 46(64)

1.95 60(61)

2.02 25(28) 1.94 55(59)

2.00 28(32) 1.93 55(60)

1.99 29(34) 2.12 33(38) 1.93 73(71)

1.96 33(37) 2.06 37(43) 2.11 129(129) 1.92 204(169)
126 . to • TO TO c TO • P *H o e TO O X

•H

o

c *H TO

4-1 *H

o 4-1 1 • CO 4-1 •H TO TO H 4-» TO 4-1 4-1 P 4-1 TO P TOD O

QJP 4-1 QJ

d 4J •H QJ C •H TO

L« *H QJ Li rH O Li *H O QJ O U 4-1 rH

QJO 4J

d rH

C Ll

c TO TO *H TO u 0) d l. rH C TO TOD •H TO rH TO P •H E a

CO rH TO > o

4-1

a rH 0) TOD XL

CD a. QJ 4-1 Jo o Li O

X

C

Q

O r*->

c CL

X

MU 5X rHo S-X

M <d rH rH rs > td :s s-< rH 50 d l.

QJ w* 4-1

o

o

QJ L<E TOD *H *h

d

rH Li

OP TOD

P 4-1 *H

-O (1) Li TO

c •pH to

e

CO 4-1 4-1 TO rH 4J

W

H QJ Lt rH

d

Li TO Ll TO a)

d

CL

P TO 4-1 *H

O

TOd TO Li *H

4J •H TO fO

O 4-1

ca rH

U TO

0)

a CJ TO 4-1 Li rs h d

CO

O© Li

X QJ

a •‘3’ <r

O TO *H

a

Ooo 1 u < CL. a o xCO

QJU

CQ

4-> CO

CM • 00 CO

c co rH in o 00 CO pH m

«H rH

4-1 CO00co

iHWx4J00d

QJLi /-v

4-1 *H

o

mo

UO CD vO

o SO

o

a. CO in

QJ ^rH CM vo n- H CM CO

CDc

<u H <

CO

CO

CO TO

ffl

s QJ « M

4-1 CO *H

O *3-

o « W v£> 00 co

tod a. CM co OV CO

CO rH

W CO CO CM

O'. QJ cm *H5*

4J

to

cd TO M QJ M a 2 > co 3 H rH

QJ 3 in in

m

rH Ll TOD

oo

o

m

jq QJ

o rH rH rH

o

co

sX ^ rH

H Jo •H

X

XX

pH QJ

®

X

o rH Q, OV CO

m

CL *H ' CM >3- co vo

TO - • • • •

4-4

P CO <r

o CM

o QJ H

CDQJ

4-1 < * CQ CJQ

Ll 1 1 1 QJ QJ QJ QJ QJ a P P d d o QJ QJ 0) 0) u rH rH rH rH

cl So 5o 5o 5o iH a CL CL a

QJ TOo

O

O

o

rH *HuUu

H

*H

H cl

a CL CL

to QJ 5o 5o 50 5o c 4-1 rH rH rH pH

QJ TO

oO

oO

H

X CL CL. CL, CL,

H 5o

QJ rH

O rH 1 pH

4J rH

d to

TO QJ Li rH •H • U TO • *» QJ • 4-1 X QJ CL • TO pH d TO d <4-1 d d rH o d QJ o 0) TO o o TO *ri o Li 4-1 Li Q> •H •H Li 4-1 •H QJ cl d 4J

4-1 TO TO 4J IM

m TO TO

TO CL 4-1 TO QJ M3- TO rH 4-1 4J d 4-1 Li •H CL d d X QJ d a +1 X QJ

<u 4-1 *H 0) TO /TV •H O Li •H TO TO 1 o Li

Li

XO Li *H CJ CJ CM

O

O

O

X

O TO 4J TO •H <U v-' 4-1 Li d d L 1 CJ X d

TO

o QJ TO CJ 4-1 QJ QJ

d •H TOD

d 4-1X TOD CO 4-1 •H TO X TO X LI pH TO > rH 4-1 4-1 >

CL 4-1 QJ

a *H TOD •H TOD QJ

d 3 d 5 c

r-*-\ 0)

O TO TO

O

O *H

d

o TOD TOD

d

rH Li rH QJ QJ QJ

X rH O » rH 4-1 d 4-1 *

*-r' 5o w-*

d TO

d

o

TO 4J a> rH QJ 4-1

&

TOD *H •H TOD *H CL •H • •H d X d d Li Li rH 0) d

TO TO *H TO

O L-4O Q>

d

H 1 rH y rH TO rH

Li TO rH Li TO TO rH rH rH

TO TO TO QJ

o QJ TO CL TO

d TOD 4-1

d 4-1 4-1 4-1 Li 4J

TO

d TO TO *H •H TO

H TO rH TO & CL pH rH rH rH CL g & a pH QJ rH

TO

O TO rH TO ?o QJ CJ *"s •rH /—

4J pH 4-1 rH

o

X Li

o TO TO TO rH 4-1 Li

*3- O

TO1 Oo

oCM

&

L4

TO

o

OO

(J CL

U CL CJ 4-1 4-1 CL

00 CM

m • • m CM CM

CO CO o O o

o

m

o

o

o

rH 00 rH

00

m

m

m

CM rH

OO

o

o

vO

o

M3-

mo CO

CM 1"*.

m

m in o m m o

pH

o

o rH

rH rH

X

XX

X

vO *3- O rH Ov o

rH rH ^3- CO

w < « 1 < Q 1 1 QJ 1 1 QJ QJ d QJ 0) 4-1 4J

0)

dd TO TO rH < QJ QJ P C

5o 1 rH pH

O

o

a pH 5o 5o

X -O

o iH

XX Li Li

Li 1 4-1 4-1 TO TO CL d QJ QJ CJ CJ 50 o 5o 5o 5o 5o rH *H rH rH rH rH o 5o O o o o

CL,

Z CL CL CL CL
127

Glossary

Isotactic Polypropylene:

R

Polypropylene is a member of the polyolefin family of polymers, [-CH^ - CH-]

where -R is an alkyl side group. In the case of polypropylene -R is -CH^. One

of three types of stereoisomeric chains of polypropylene (or other polyolefins) can

be synthesized depending on the type of catalyst and the conditions used in the

polymerization process. The three types of chains differ from one another in the

dispositions of the side groups, -R, relative to the backbone carbon atoms in the

chains. The configurational differences between the three types of chains are demonstrated in Fig. 25 where, for the sake of simplicity in illustration the backbone

carbon atoms are depicted to be in a planar zig-zag conformation. Fig. 25a represents

an isotactic chain which is characterized by the fact that all the side groups occur

on the same side of the plane which contains the backbone carbon atoms. Fig. 25b

represents a syndiotactic chain in which there is a regular alternation of successive

side groups from one side to the other of the plane containing the backbone carbon

atoms. Fig. 25c depicts a chain in which successive side groups occur randomly, on

one side or the other, relative to the plane of reference, such chains are referred

to as atactic . Isotactic and syndiotactic polypropylene undergo crystallization,

atactic polypropylene does not. [A detailed discussion of tacticity in polyolefins

and other polymers may be found in "Stereoregular Linear Polymers" by I. Pasquon in

"Encyclopedia of Polymer Science and Technology", Vol. 13, pp. 13-86, (Interscience

Publishers, New York, 1970)].
128 -

Figure 25; Illustration of the chain configuration in (a) isotactic, (b)

syndiotactic and (c) atactic chains in polyolefins (see text)
-129-

Wide Angle and Small Angle X-ray Diffraction (WAXD and SAXD)

In both the wide angle and small angle x-ray diffraction experiments described

in this report, the polymer samples were exposed to pinhole collimated x-ray beams,

and the diffracted rays were recorded on photographic film. The terms wide angle

and small angle refer to the range of angles, between the incident x-ray beam and

the diffracted rays, over which the diffracted rays are recorded. In WAXD the

range is from a few degrees to 30-50°, whereas in SAXD the range is from a few

seconds of arc up to one degree or so. [A brief introduction to the type of

information which can be derived from WAXD and SAXD regarding the fine structure

V of polymers is given in "Experiments in Polymer Science" by E . A. Collins, J. Bares,

and F. W. Billmeyer, Jr., pp . 191-197 (Wiley- Interscience , New York, 1973). More

advanced treatments of the use of WAXD and SAXD in polymer structure characterization

are given in "X-ray Diffraction Methods in Polymer Science" by L. E. Alexander

(Wiley- Interscience , New York, 1969],

Orthorhombic, Monoclinic, Triclinic:

Crystal lattices are conveniently grouped according to seven types of conventional unit cells, three of which are the orthorhombic, the monoclinic and the

triclinic cells. The unit cell axes are conventionally denoted a, b and c, and

the angles between these axes are denoted a, B, and y, where a = b c, (3 = a^c, and

y = a\. In orthorhombic cells a^b^c,a = B = y

= 90°; in monoclinic cells a ^ b ^

c, a = y

= 90° ^ B; in triclinic cells a^b^c, a^B^Y* [For a discussion of

the fundamental types of crystal lattices see "Introduction to Solid State Physics",

by C. Kittel, pp . 12-33 (John Wiley and Sons, New York, 1971, 4th Ed.)].

Distribution List

No. of Copies

High Voltage Measurements Section 75

Electricity Division

National Bureau of Standards

Washington, D.C. 20234

Dr. R. K. Eby 10

Chief, Polymers Division

National Bureau of Standards

Washington, D.C. 20234

Dr. M. Broadhurst 1 Polymers Division

National Bureau of Standards

Washington, D.C. 20234

Dr. B. Fanconi 1 Polymers Division

National Bureau of Standards

Washington, D.C. 20234

Dr. F. I. Mopsik 1 Polymers Division

National Bureau of Standards

Washington, D.C. 20234

Dr. F. Khoury 1 Polymers Division

National Bureau of Standards

Washington, D.C. 20234

Mr. J. P. Colson 1 Polymers Division

National Bureau of Standards

Washington, D.C. 20234

Mr. L. H. Boltz 1 Polymers Division

National Bureau of Standards

Washington, D.C. 20234

131
No. of Copies

Mr. S. J. Kryder

Polymers Division

National Bureau of Standards

Washington, D.C. 20234

Mr. E. B. Forsyth

Brookhaven National Laboratory

Associated Universities, Inc.

Upton, Long Island, N.Y. 11973

Dr. W. E. Keller

Los Alamos Scientific Laboratory

University of California

Los Alamos, New Mexico 87544

Dr. Mario Rabinowitz

Electric Power Research Institute

3412 Hi 11 view Avenue, P.0. Box 10412

Palo Alto, California 94303

Mr. A. C. Muller

Brookhaven National Laboratory

Associated Universities, Inc.

Upton, Long Island, N.Y. 11973

Mr. A. J. McNerney

Brookhaven National Laboratory

Associated Universities, Inc.

Upton, Long Island, N.Y. 11973

Dr. R. W. Meyerhoff

Union Carbide Corporation

Linde Research Laboratories

Tarrytown, N.Y. 10591

Dr. R. J. Densley

Power Engineering Section

National Research Council

Ottawa, Canada K1A 0R8

- 132 -

*U . S . GOVERNEMNT PRINTING OFFICE: 1977 - 740 - 0S2/ 62