NBS SPECIAL PUBLICATION 260-31

Standard Reference Materials:

THERMAL CONDUCTIVITY OF

ELECTROLYTIC IRON,

SRM 734, FROM 4 TO 300 K
NATIONAL BUREAU OF STANDARDS

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j 5 1971

I

UNITED STATES DEPARTMENT OF COMMERCE • Maurice H. Stans, Secretary J . £ NATIONAL BUREAU OF STANDARDS • Lewis M. Branscomb, Director

\ r

Standard Reference Materials:

Thermal Conductivity of Electrolytic Iron,

SRM 734, From 4 to 300 K

J. G. Hust and L. L. Sparks

Institute for Basic Standards

National Bureau of Standards

Boulder, Colorado 80302

4 , National Bureau of Standards Special Publication 260-31

Nat. Bur. Stand. (U.S.), Spec. Publ. 260-31, 19 pages, (Nov. 1971) CODEN: XNBSA

Issued November 1971 For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. C13.10:260-31). Price 35 cents.

PREFACE

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.

This 260 Series is dedicated to the dissemination of

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vi
TABLE OF CONTENTS

PAGE

Introduction 2 Apparatus and Data Analysis 3 Specimen Characterization 3 Results 7 Summary 8 Acknowledgements 8

LIST OF FIGURES

PAGE

Figure No.

1. Thermal Conductivity Deviations for

Electrolytic Iron (SRM 734) 10

2. Thermal Conductivity of Electrolytic

Iron (SRM 734) 11

LIST OF TABLES

PAGE

Table No.

1. Residual Resistivity Ratio of Electrolytic Iron (SRM 734) 12

2. Parameters for Equation (4) 13

3. Thermal Conductivity of Electrolytic

Iron (SRM 734) 14

vii

THERMAL CONDUCTIVITY OP ELECTROLYTIC IRON,

SRM 734, from 4 to 300 K*

J. G. Hust and L. L. Sparks

Institute for Basic Standards

National Bureau of Standards

Boulder, Colorado 80302

Thermal conductivity data are reported for a specimen

of electrolytic iron, SRM 734, for temperatures from 4 to 300 K. Variability of this iron was studied by means of

electrical residual resistivity ratio measurements on 63 specimens . This study showed that with a two-hour anneal

at 1000 °C one can obtain a thermal conductivity Standard

Reference Material that has variability of less than 1% in

thermal conductivity.

Key words: Cryogenics; electrical resistivity; electrolytic iron; Lorenz ratio; Seebeck effect;

thermal conductivity; transport properties.

*This work was carried out at the National Bureau of

Standards, Boulder, Colorado under the sponsorship of the

NASA-Space Nuclear Propulsion Office, Cleveland, Ohio, and

the National Bureau of Standards Office of Standard Reference Materials (NBS-OSRM) , Washington,. D.C.

1
INTRODUCTION

This report results from a program to establish several

thermal conductivity Standard Reference Materials (SRM's).

Measurements are planned for Standard Reference Materials in

the high, medium, and low conductivity ranges. The material

reported on here, electrolytic iron SRM 73^ [1], is in the

high-to-medium range of conductivity.

Design and development engineers in the aerospace industry continue to have urgent need for thermal and mechanical

property data for new materials. For most materials, especially new or uncommon alloys, measured values of thermal

conductivity are not available and predictions cannot be

made with adequate confidence. To help satisfy these needs,

we have constructed an apparatus for the simultaneous mea- surement of thermal conductivity, electrical resistivity and

thermo-power . Another phase of this program, to establish

standard reference data on several Standard Reference Materials, has begun. We intend to measure several specimens of

materials that appear to be useful as standards. Standard

Reference Material data are useful for intercomparison of

existing thermal conductivity apparatus, for debugging new apparatus, and for calibration of comparative apparatus.

The apparent large differences among the results of various

investigators for a given material (50% is not unheard of)

is evidence of the need for intercomparisons , calibrations,

and standardization. The availability of Standard Reference

Materials will result in more accurate and more permanent

transport property data for t echxii_caJLly important solids.

The basic characteristics of a thermal conductivity

Standard Reference Material are that it be: (a) stable and

reproducible under the conditions of use, (b) uniform

throughout a single specimen and from specimen-to-specimen,

(c) similar in property value to the material that is to be

determined in terms of it, (d) readily machined and fabricated in appropriate size and shape, (e) chemically inert to

2
the materials in the system to which it will be exposed, and

(f) usable over a wide range of temperature. Electrolytic

iron, SRM 73^, does not satisfy (e) and (f) as well as might be desired; however, its availability from the Office

of Standard Reference Materials (OSRM) in a large homogeneous lot and the past use of a similar iron as a thermal

conductivity standard is considered sufficient justification

for this work.

APPARATUS AND DATA ANALYSIS

The apparatus is based on the axial one-dimensional heat

flow method. The specimen is a cylindrical rod 3-6 mm in

diameter and 23 cm long with an electric heater at one end

and a temperature controlled sink at the other. The speci- men is surrounded by glass fiber and a temperature controlled shield. Eight thermocouples are mounted at equally

spaced points along the length of the specimen to determine

temperature gradients in the range 4 to 300 K. The experimental data are represented by arbitrary

functions over the entire range and smooth tables are generated from these functions. The number of terms used to represent each of the data sets is optimized, through the

use of orthonormal functions, so that none of the precision

of the data is lost by underfitt ing , nor are any unnecessary

oscillations introduced by overfitting. A detailed description of this apparatus and the methods of data analysis are given by Hust, et al. [2]

SPECIMEN CHARACTERIZATION

Density as measured by air and water weighings (see

Bowman, et al . [3]) is 7.867 + 0.005 g/cmJ. Rockwell hardness and grain size are B23-5 and 0.0507 mm, respectively.

The grain size was determined by the American Society for

Testing and Materials (ASTM) comparative method. Each of

these values is for the material in the annealed state as described later. The purity of this electrolytic iron is

3
99-9 + wt . percent. The material is similar in composition

to SRM 1265, electrolytic iron, which is certified for its

chemical composition. The certificate of analysis for SRM

1265 is shown as Appendix I. Electrical resistivity, p, and thermal conductivity,

A, of metals, especially pure metals, are intimately related. This relationship exists because most of the heat

transfer in a metal is caused by the electrons. Some heat

is also transported by the lattice vibrations. The total

conductivity is therefore the sum of the electronic, A , and the lattice, A , (the German word for lattice is Gitter)

D components

.

A = A eg+ A (1)1 In most pure metals A is small compared to A : but in

transition metals A may be as large as 20% of A . For pure

g e metals and dilute alloys, the relationship between p and A at both high and low temperatures is reasonably well described

by the Wiedemann-Franz-Lorenz (WFL) law:

ip = L

q

= 2.443 x 10" 8 V

2 K-2

(2)

For our purposes the ice point is a sufficiently high tem- perature and liquid helium is a sufficiently low temperature

to satisfy the WFL law. In metals there are two mechanisms that account for most

of the scattering of electrons: the interaction of electrons

with chemical impurities and physical imperfections, and the

interaction of electrons with the thermal vibrations of the

ions of the lattice. The former mechanism is independent of

temperature while the latter is temperature dependent. If

we assume that each of these mechanisms is independent of

the other, we may assign a separate resistivity to each.

The resistivity arising from impurity and imperfection scat- tering is usually referred to as the residual resistivity,

4
p , while the resistivity due to thermal scattering is

called the intrinsic resistivity, p^CT). The total resistivity, p(T), may be written as the sum of these two terms:

p(T) = p Q + P± (T) (3)

This separation of the total resistivity into a constant

term (p

q

) and a temperature dependent term (p^(T)) is known

as Matthiessen ' s rule. Although Matthiessen ' s rule is not strictly valid, it is a sufficiently good approximation for our purposes

.

At ambient temperatures the residual resistivity is a negligibly small fraction of the total resistivity; con- sequently, the total resistivity, p(T), is nearly equal to the intrinsic resistivity, p^(T), and therefore a characteristic of the metal itself. As the temperature approaches

absolute zero, however, the intrinsic resistivity becomes

very small and the total resistivity is essentially the

value of p Q. The temperature at which p(T) becomes con- stant depends upon the purity of the sample, but for most

materials available at the present time, the intrinsic re- sistivity will be negligible at 4 K (the boiling point of

helium)

.

The residual resistivity which is caused primarily by

impurities and imperfections, provides a good indication of

a specimen's purity and freedom from strain. Rather than

using the residual resistivity itself for this purpose, the

usual procedure is to determine a specimen's resistance at the ice-point, ^273* an<^ at ^ ^' R

4

3 and to calculate the

ratio between these two, R^^/R^. This is nearly equal to the ratio of the resistivities at the same temperatures as the geometric form factor nearly cancels in the ratio. The

geometric form factors are not quite the same because of

thermal expansion, which is seldom over 0.5%. This ratio

is called the residual resistivity ratio, RRR, and its

magnitude is an indication of the purity and physical per5
fection of a specimen. [4] Thus the variability in RRR for

various specimens in a given lot of material is an indication of the variability in chemical impurity concentration

and physical imperfection concentration in the lot. Such

variability also affects the thermal conductivity as indicated by the WPL law. Therefore, a determination of RRR variability will directly indicate thermal conductivity

variability. The determination of RRR is considerably

easier than the determination of A. An extensive resistivity variability study was con- ducted on this electrolytic iron, the object being to determine if it could be heat treated in such a manner that

the thermal conductivity variability would be acceptably

small. This was achieved with a 2-hour, 1000 °C anneal in

either a vacuum or helium atmosphere. The results of this

study are shown as residual resistivity ratios in table 1. The ratio given is resistivity at 273.15 K to resistivity

at 4 K . Specimens labeled C2T, A6L, C5L, AIL, and A5T were obtained from the 6.35 mm diameter rods; the remaining

specimens were machined from 31-8 mm diameter rods. Based

on the 63 residual resistivity ratio measurements made on these specimens in various stages of heat treatment, the

following is concluded: The specimens machined from the

large diameter rods are significantly different in residual

resistivity ratio from the unmachined specimens in the as received condition. The ratio of the unmachined rods is

22.01 + 0.20 while the ratio of the machined rods is 19.52 + 0.44

Various heat treatments were tried to remove the differences in ratio of the two sets of rods. After heat treating at 500 °C for 1 hour, the ratios increased but were still

different (ratio of unmachined rods = 23.53 + 0.20; ratio of

machined rods = 22.14 + 0.34). Raising the temperature to 1000 °C for 2 hours produced rods which are indistinguishable, (ratio of unmachined rods, 23.39 + 0.28; ratio of

6
machined rods, 23.29 + 0.20; ratio of all rods, 23.33 + 0.24).

The variation shown is 2s, where s is the estimated standard deviation and includes material and measurement variability. To study the possibility of a change in these ratios

with age, one set of rods was measured after about 50 days

from the 1000 °C treatment; no significant change was detected (23.40 + 0.20)

.

These measurements show that electrolytic iron SRM 734 can be used as a thermal conductivity standard below room temperature with an estimated material variability of about

+ 1% if annealed at 1000 °C for 2 hours.

RESULTS

The thermal conductivity of specimen A5T was measured.

The experimental data were functionally represented with the

following equation:

n . inX = a[£nT] 1 (4)

1=1

where X = thermal conductivity and T = temperature. Temperatures are based on the IPTS-68 scale above 20 K and the NBS

P2-20(1965) scale below 20 K. The parameters, a^, determined

by least squares, are presented in table 2. Further details

of this procedure are described by Hust, et al. [2] The deviations of the experimental data from these equations are given in' figure 1. Calculated values of X are presented in

table 3 and in figure 2. A detailed error analysis for this system has been presented previously by Hust, et al . [2] Based on this analysis

of systematic and random errors, the uncertainty estimates

(with 95$ confidence) are as follows:

k 2.5$ at 300 K, decreasing as T to 0.70$ at 200 K,

0.70$ from 200 K to 50 K, increasing inversely with

temperature to 1.5$ at 4 K.

7
SUMMARY

We have established low temperature thermal conductivity

standard reference data for electrolytic iron SRM 73^. Thermal conductivity measurements have been made on this iron

from 6 to 300 K. These data were fitted to an empirical

equation that was used to generate tabular values. Material variability is estimated to be less than + 1% in thermal

conductivity, and measurement uncertainty is less than 2.5%,

i ACKNOWLEDGEMENTS

We wish to thank R. E. Michaelis of NBS 3 OSRM, for supplying these specimens along with helpful discussions. This

measurement program has been carried out under the helpful

guidance of R. L. Powell.

8
FOOTNOTES AND REFERENCES

[1] This SRM is available in the form of rods of two different diameters and may be ordered from the Office of

Standard Reference Materials, National Bureau of Standards, Washington, D.C. 202 34 . SRM 734-S is a rod 6.4 mm (1/4 in.) in diameter and 305 mm (12 in.) in length.

SRM 734-L1 is a rod 31.8 mm (1 1/4 in.) in diameter and

152 mm (6 in.) in length; SRM 734-L2 is the same diameter

but 305 (12 in.) in length. Longer continuous lengths

can be obtained by special order to the OSRM.

[2] Hust, J. G . , Powell, Robert L . , and Weitzel, D. H.,

Thermal Conductivity Standard Reference Materials from

4 to 300 K: I. Armco Iron: Including Apparatus De- scription and Error Analysis, J. Res. Nat. Bur. Stand.,

(U.S.), 74A(Phys. and Chem.) 673-690(1970).

[3] Bowman, H. A., and Schoonover, R. M., Procedure for High

Precision Density Determinations by Hydrostatic Weighing,

J. Res. Nat. Bur. Stand., (U.S.), 71C (Engr . and Instr.)

179-198(1967).

[4] Since the specimens were in the annealed condition the RRR value should indicate the effective chemical purity

(electrical purity) of the specimen. Using the specific resistivities listed by Blatt [5] and the mea- sured chemical composition of this iron we obtain a residual resistivity of 5 nftm if all of the impurities

were in solution. Since the measured residual resistivity is 4 nftm, the electrical purity is essentially

the same as the chemical purity, 99 • 9 %

•

[5] Blatt, F. J., Physics of Electronic Conduction in Solids,

p. 199 (McGraw-Hill Book Co., Inc., New York, N. Y.,

1968) .

9
»n CM

10
TEMPERATURE (kelvin)

Figure 2. Thermal conductivity of electrolytic

iron (SRM 73^)

11
Table 1. Residual resistivity ratio (p 273 K / P 4 k) °f electrolytic

iron SRM 734

Specimen Ratio

As

received

500°C

lhr

500°C

8hr

1000°C

2hr

400 °C

Z~ days

Aging

50 days

C2T

A6L

C5L

AIL

A5T

21. 97(a) 22. 16 21.94

22. 04

22. 03(b)

23. 53 24. 12 23. 31(e) 23.22(f)

23.40(f)

23. 59(°) 23. 42(t)

24. 84

24. 85

25. 00

24. 97 23.47

23. 52

23. 42

7 A 11-11 2A-1-2

2A-1-3

2A-1-4

J - 1 2A-3-2

2A-3-3

2A-3-4

19. 35

19. 50

19. 30

19. 38

19. 77

19. 92

19. 73 19.93

21.96 22. 32 23.47(e)

23. 31(c) 25. 12 25. 24 23.35

23. 27( ± ) 23.20(e)

23. 20(c) 21. 83 22. 25 24. 94 25. 01 23. 25( d )

-

- 1 - 1 2C-1-2

2C-1-3

2C-1-4

19. 42

19. 12 19.46

19. 56

21. 70 22. 00 23. 23(e)

23.41(c)

< 23.44

23.40

2C-3-1

2C-3-2

2C-3-3

2C-3-4

19. 34 19.49

19. 57 19.40

21.93 21.99 23.27(e) 23.40

(a) repeat measurement, 21.91

(b) ratio of A5T thermal conductivity specimen, 21.89

(c) these were heat treated in vacuum, the remaining were

heated to 1000°C in a helium atmosphere (1 atm pressure),

(d) repeat measurements , 23. 39, 23. 31

(e,f) these were done in separate heat treatments to detect reproducibility of heat treatment

12
Table 2. Parameters for equation (4)

a.

i

1 -1. 48463068 X 101 2 6. 93779265 X 101 3 -1. 13470636 X 102 4 1 01420592 X 102 5 -5 68004853 X 101 6 2 10770015 X 101 7 -5 27537674 X 10°

8 8 81839451 X 10"

9 -9 43950407 X 10"

10 5 85191930 X 10"

11 -1 59785857 X

10"'

13
Table 3. Thermal conductivity of electrolytic iron (SRM 734)

Thermal

Temp Conductivity (K) (Wm_1 K" 1

) 6 38. 8

7 45. 3 8 51. 8

9 58. 2 10 64. 7 12 77.4

14 89. 7 16 101

18 113

20 123

25 146

30 162

35 171 40 173 45 171 50 167

55 160

60 153

65 145 70 139

Thermal

Temp Conductivity

(K) (Wm" 1 K" 75 132

80 127

85 122

90 117

95 114

100 110

110 105 120 101 130 98. 3 140 95. 8 150 93. 8 160 92. 0 170 90. 3 180 88. 9 190 87. 5 200 86. 2 220 84. 0 240 82. 3 260 80. 8 280 79. 3

14
U. S. Departing' of Commerce

Maurice .H. Stans

Secretary

i >>«." &j

National Bureau of Standards

L. M. BrartWmts, Director Rational ^ttram of jltatttlattte

Certificate of JVnalgsts

Standard Reference Material 1265

Electrolytic Iron

This standard is in the form of disks 32 mm (1 1/4 in) in diameter and 19 mm (3/4 in) thick, generally for use in optical emission and x-ray spectrometric analysis.3 Element Percent, by weight Carbon 0.0067 Manganese 0057

Phosphorus 002s Sulfur 0059

Silicon 0080 Copper 0058

Nickel 041 Chromium 0072 Vanadium 0006 Molybdenum 0050

Cobalt 0070 Titanium 0006

Arsenic (.0002)b Aluminum (Total) (.0007) Boron 00013

Lead 00002

Iron (by difference) 99.9

a This material also is available in the form of chips, SRM 365, for use in chemical methods of analysis; rods, SRM 1099, 6.4 mm

(1/4 in) in diameter and 102 mm (4 in) long for the determination of gases in metals by vacuum fusion and neutron activation methods of analyses; and rods, SRM 665, 3.2 mm (1/8 in) in diameter and 51 nun (2 in) long for application in microchemical methods of analysis such as electron probe microanalysis, spark source mass spectrometric analysis, and laser probe analysis. bValues in parenthesis are not certified since they are based on the results from a single laboratory. CERTIFICATION: The value listed for a certified element is the best estimate of the true value based on the results of the cooperative analytical program. The value listed is not expected to deviate from the true value by more than ±1 in the last significant figure reported; for a subscript

figure, the deviation is not expected to be more than ±5. Based on the results of homogeneity

testing, maximum variations within and among samples are estimated to be less than the accuracy

figures given above.

Washington, D. C. 20234 J. Paul Cali, Chief August 6, 1971 Office of Standard Reference Materials

(over)
PLANNING, PREPARATION, TESTING, ANALYSIS: This standard is one of five replacements!

for the original eight 1100 series iron and steel SRM's. Material from the same melt is available in a variety of forms to serve in checking methods of analysis and in calibrating instrumental techniques. The material for this standard was vacuum melted and cast at the Carpenter Technology!

Corporation, Reading, Pennsylvania, under a contract with the National Bureau of Standards. The

contract was made possible by a grant from the American Iron and Steel Institute. The ingots were processed by Carpenter Technology Corporation to provide material of the

highest possible homogeneity. Following acceptance of the composition based on NBS analyses, selected portions of the ingot material were extensively tested for homogeneity at NBS by J. R. Baldwin, D. M. Bouchette, S. D. Rasberry, and J. L. Weber, Jr. Only that material meeting a critical evaluation was processed to the final sizes. Chemical analyses for certification were made on composite samples representative of the; accepted lot of material. Cooperative analyses for certification were performed in the Research Laboratories of Armco

Steel Corporation by R. L. LeRoy and J. F. Woodruff.

Analyses were performed in the Analytical Chemistry Division of the National Bureau of Standards by the following: R. Alvarez, J. R. Baldwin, E. Belkas, B. S. Carpenter, M. M. Darr, E. R. Deardorff, E. L. Garner, T. E. Gills, L. A. Machlan, E. J. Maienthal, L. J. Moore, C. W. Mueller, T. J. | Murphy, P. J. Paulsen, K. M. Sappenfield, B. A. Thompson, and S. A. Wicks. The overall direction and coordination of the technical measurements at NBS leading to certifi- cation were performed under the direction of 0. Menis, B. F. Scribner, J.I. Shultz, and J. L.

! Weber, Jr. The technical and support aspects involved in the preparation, certification, and issuance of this Standard Reference Material were coordinated through the Office of Standard Reference Materials by R. E. Michaelis.
ij ADDITIONAL INFORMATION ON THE COMPOSITION: Certification is made only for the

I elements indicated. The five replacements, however, contain a graded series for 40 elements and

|| information on the elements not initially certified may be of importance in the use of the material.

;| Although these are not certified, upper limit values are presented in the following table for the

! remaining elements. (Some may be certified at a later date.)

j Elements Detected (ppm by weight)

1 Upper (Estimated Element Limit value) W < 1 ( 0.4 ) Sn < 5 ( 2 ) |Nb < 0.5 (<0.1 )

1 Ag <s U.Z ( 0.02)

j Zn < 3 ( 2 ) In <20 (Ml ) Ge <50 (~14 ) Jo <70 /AO \ ( °3 ) H < 5 ( 1 )

! Elements Sought But Not Detected (ppm by weight)

11 r

! Upper

1 Element Limit Ta <0.5

Zr <0.1

Sb <0.5

Bi <0.1

Ca <0.1 Mg <0.2

Se <0.1

Te <0.1

Ce <0.05

La <0.05

Pr <0.05 Au <0.02

Hf <0.2 Nd <0.05

Method

Neutron activation Spark source mass spectrometry Spark source mass spectrometry Spark source mass spectrometry Spark source mass spectrometry

Distillation-photometric Spark source mass spectrometry Vacuum fusion Vacuum fusion

Method

Neutron activation Spark source mass spectrometry Neutron activation Spark source mass spectrometry Atomic absorption Atomic absorption

Spark source mass spectrometry Spark source mass spectrometry Spark source mass spectrometry Spark source mass spectrometry Spark source mass spectrometry Neutron activation Spark source mass spectrometry Spark source mass spectrometry

orm NBS-114A (1-71)

! U.S. DEPT. OF COMM. 1 . PUBLIC ATION OR REPORT NO. 2. Gov't Accession bibliographic data Spec. Publ. 260-31 No* 3. Recipient's Accession No.

TITLE AND SUBTITLE Thermal Conductivity of Electrolytic

Iron SRM 734 , from 4 to 300 K

5. Publication Date November 1971

6. Performing Organization Code

7. AUTHOR(S) J. G. Hust and L. L. Sparks

8. Performing Organization r

!

2.

t

PERFORMING ORGANIZATION NAME AND ADDRESS NATIONAL BUREAU OF STANDARDS DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 3020585

11. Contract/Grant No.

Sponsoring Organization Name and Address Same

13. Type of Report & Period Covered Final

14. Sponsoring Agency Code

5. SUPPLEMENTARY NOTES

j6. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

j bibliography or literature survey, mention it here.) Thermal conductivity data are reported for a specimen of

electrolytic iron, SRM 734, for temperatures from 4 to 300 K. Variability of this iron was studied by means of electrical

residual resistivity ratio measurements on 63 specimens. This

study showed that with a two-hour anneal at 1000 °C one can obtain a thermal conductivity Standard Reference Material

that has variability of less than 1% in thermal conductivity.

If. KEY WORDS (Alphabetical order, separated by semicolons)Cry Ogeni C S ; electrical res Istlvlty ; electrolytic iron; Lorenz ratio; Seebeck effect; thermal con- ductivity; transport properties

18 AVAILABILITY STATEMENT 19. SECURITY CLASS

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21. NO. OF PAGES

19 E UNLIMITED. UNCLASSIFIED

1 1 FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE

TO NTIS.

20. SECURITY CLASS

(THIS PAGE) UNCLASSIFIED

22. Price 35*

USCOMM-DC 66244-P71
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