NATL INST. OF STAND & TECH _,

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1 1! II PUBLICATIONS

AIlIDt tMt,375

NIST Technical Note 1531

DC Conductivity Measurements

of Metals

^ It J^*J S^ '' '"stitute of Standards and Technology

gy Administration, U.S. Department of Commerce IB3\

Michael D. Janezic

Raian F. Kaiser

James Baker-Jarvis

George Free

NIST Technical Note 1531

DC Conductivity Measurements

of Metals

Michael D. Janezic

Raian F. Kaiser

James Baker-Jarvis

George Free

Electromagnetics Division

Electronics and Electrical Engineering Laboratory

January 2004

U.S. Department of Commerce

Donald L. Evans. Secretary

Technology Administration

Phillip J. Bond Under Secretary ofCommercefor TechnologyNational Institute of Standards and TechnologN

Arden L. Bement. Jr.. Director
Certain commercial entities, equipment, or materials may be identified in this document in order to describe an experimental procedure or concept adequately. Such

identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the

entities, materials, or equipment are necessarily the best available for the purpose.

National Institute of Standards and Technology Technical Note 1531

Natl. Inst. Stand. Technol. Tech. Note 1531, 20 pages (January 2004)

CODEN: NTNOEF

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 2004

For sale by the Superintendent of Documents, U.S. Government Printing Office

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Mail: Stop SSOP, Washington, DC 20402-0001
Contents

1 Introduction 1

2 Theory of Electrical Conductivity 2

2.1 Classical Model of Electrical Conductivity 2

2.2 Quantum Model of Electrical Conductivity 4

3 MeEisurement of DC Conductivity 5

3.1 Measurement System 5

3.2 Measurement Theory 6

3.3 Measurement Procedure 7

3.4 Uncertainty Analysis 8

4 DC Conductivity Measurements 10

4.1 Verification of Measurement System 10

4.2 Measurements of DC Conductivity 11

4.3 Measurements of Variable Temperature DC Conductivity 12

5 Conclusion 13

6 References 14

Appendix A. Certificate for SRM 1461 15

ni

DC Conductivity Measurements of Metals

Michael D. Janezic, Raian F. Kaiser, James Baker-Jarvis, and George Free

Electromagnetics Division, National Institute of Standards and Technology,

Boulder, CO 80305

We examine a measurement method for characterizing the dc conductivity of metal

alloys commonly used in the manufactiore of weapons. From accurate measurements

of the voltage and current across a cylindrical metal sample, we calculate the metal's

dc conductivity. Equations for the dc conductivity are derived from first principles, in- cluding a detailed uncertainty analysis. In a measurement comparison with a National

Institute of Standards and Technology (NIST) Standard Reference Material (SRM)

for conductivity, we verified the performance of our measurement system. Using this

system, we measured the dc conductivity of ten metal alloys over a temperature range

of 15 to 40 °C.

Key words: dc conductivity; metal; resistivity; temperature; weapons.

1. Introduction

In this paper we summarize a technique for measuring the dc conductivity of metals commonly used in weapons, and present electrical conductivity results for several metaJ alloys as a function of temperature. Although the conductivity of many metals can be found in the

literature, the values are often for only a particular alloy or at a specific temperature. As new- metal alloys are developed the conductivity of some metals remains unknown or unpublished,

which is a problem for designers and manufacturers who require accurate conductivity data.

As a result, we constructed a system for measurement of dc conductivity that can accurately measure the conductivity of a wide range of metals using easily machined cylindrical met ad rod samples.

1
We begin this Tech Note with a brief introduction to the classical and quantum-mechanical

theories for describing electrical conduction in metals. This chapter provides some description of the phenomenon of electrical conductivity and gives the reader some insight into the

temperature dependence of metal conductivity.

Following this introductory chapter, we overview a technique for measuring the dc conductivity of metals. We begin by describing our measurement system and follow with a

section that derives the necessary equations used to calculate the conductivity of a metal

rod. Also covered in this chapter are a description of the measurement procedure and a

detailed uncertainty analysis.

In the final chapter, we present the measurement results for 10 different metal alloys

that cover a wide range of conductivities. We first verified the conductivity measurement

system using a National Institute of Standard and Technology (NIST) Standard Reference

Material (SRM). After the verification process, we characterized the selected metal alloys

and calculated dc conductivity results at ambient temperature. Since the conductivity of

metals is temperature-dependent, in this Tech Note we also describe how we employed an

environmental chamber to broaden our temperature range from 15 to 40 °C. From results

from this system, we present temperature-dependent dc conductivity for 10 metal alloys.

2. Theory of Electrical Conductivity

2.1 Classical Model of Electrical Conductivity

For over a hundred years, physicists have attempted to describe the phenomena of electrical

conduction in metals. At the beginning of the 1900's, Drude developed his classical theory

based on the concept of a gas of free electrons. Although this theory has limitations because

it ignores the quantum behavior of the electron, the classical model does present some useful

insight into electrical conduction and the calculation of electrical conductivity.

As outlined in Reference [1], the classical model assumes that the metal consists of

immobile positive ions and freely moving negative electrons that are randomly distributed

in the metal. Some of these electrons remain bound to the positive ions while the remaining

valence electrons are free to move far from the positive ions to which they were orginally

bound. The movement of these valence electrons is modeled using the classical kinetic theory

of gases, under the following assumptions.

First, the model assumes that the valence electrons experience collisions with the immobile positive ions. However, the precise details regarding how the electron is scattered is
unspecified. The average interval between collisions for a single electron is assumed to be

r. This time constant r has several names: relaxation time, collision time, or mean free

time. Through each collision, the electron's velocity and direction are changed. Between

collisions, the model assumes that the electron does not interact with either the positive ions

(free-electron approximation) or the other valence electrons (independent-electron approximation). With these assumptions in place, the classical free-electron model is used to model

the dc electrical conductivity of a metal.

A valence electron with charge —e collides with one of the immobile positive metal ions

at time i, giving the electron a velocity Vq. When electron is affected by an applied external

electric field E, its resulting acceleration is —eE/m. The electron's velocity is now a sum

of the velocity after the collision plus the velocity due to the electron's interaction with the

electric field:

Vtotal = ^0 + • 1) m

If instead of one electron, we consider n free electrons having collisions at time i = 0,

then each electron will have a velocity of the form (1). Note however that for each electron,

vq is random and will average to zero over all n electrons. Thus the average velocity Vavg of

the n electrons is given by

_ _ -eEt

m

If no other collisions occur, the electrons would continue to accelerate. However, other collisions do occur and the classical model assumes that the average interval between collisions

is r, resulting in an average electron velocity of

- -

-^-^^

r^^

^ m

Since there are n electrons moving with an average velocity Vavg, we define a current

density J by

- ^ ne^Er

J = -nevavg = • (4 m

Prom Ohm's law we also know that

J = aE, (5)

where a is the electrical conductivity of the metal. Using these two expressions for J, we

find that a can be expressed as a= . (6) m

In Drude's time, the electrical conductivity a of metals was known to be inversely proportional to temperature. There is nothing explicit in Eq. (6) about how the conductivity
varies with temperature. Drude tried to argue that r might also have a T~^ dependence,

but this assumption was found to contradict experimental results found for the thermal

conductivity [2]. Although Lorentz tried to modify the Drude model by assuming that the

electron velocities were governed by the Maxwell-Boltzmann distribution function, it was not

until quantum theory was developed that the conductivity of metals could be adequately

described [3].

2.2 Quantum Model of Electrical Conductivity

In the previous section, we summarized the classical free-electron model theory for metal

conductivity. Because it ignored the quantum behavior of the electron it had several limitations, including the inability to predict the temperature dependence of a metal's conductivity.

In this section we discuss how quantum mechanics was employed to improve the theory of

electrical conductivity in metals, including the effect of temperature on conductivity.

In trying to improve on the classical free-electron theory of conductivity, Sommerfeld

(1928) began with some of the same assumptions used in the classical model. Included in his

model was the assumption that between collisions the electrons would have no interactions

with either the fixed positive ions or the other electrons. Sommerfeld 's improvement in the

theoretical model came when he understood that the electron velocities were governed not

by the classical Maxwell-Boltzmann distribution function, but by the quantum-mechanical

Fermi-Dirac distribution function. The development of Fermi-Dirac statistics (1926) followed

from the Heisenberg uncertainty principle (1925) and the Pauli exclusion principle (1925),

both important new ideas in quantum mechanics. With this modification, the allowed electron energy levels become discrete rather than continuous, and the number of electrons with

the same energy is restricted.

Although Sommerfeld's use of Fermi-Dirac statistics was an improvement when describing

electrical conduction in metals, his model was still inadequate because it did not adequately

describe the effect of positive ions in the metal [1]. Specifically, the model assumed that

the ions were fixed and randomly distributed throughout the metal, and did not take into

account the effect of the positive ions on the dynamics of the moving electrons. As a result,

the model could not explain why the mean free path, the distance an electron travels between

collisions, was experimentally found to be several hundred angstroms greater than expected

at room temperatures for good conductors, and significantly higher at lower temperatures.

In addition to the problem of the large mean free path, this model did not correctly predict

the temperature dependence of electrical conductivity.
A major advance in the understanding of electrical conductivity was made when new

discoveries showed that the positive ions were not randomly distributed throughout the

metal. Using X-ray diffraction experiments, the ions were found to be actually arranged

in a periodic array or lattice. With this knowledge, Bloch (1928) developed a theory for

electrons in a metal by solving Schrodinger's equation for a periodic potential array. Bloch

showed that an electron moving at a constant velocity through a perfect array of fixed ions

would continue to move at that velocity. Surprisingly, the electrons do not scatter due to the

expected collisions with the fixed positive ions. For this ideal situation involving a perfect

array of positive ions, the electrons would still create a current even if there is no impressed

electric field, resulting in infinite conductivity. However, due to the small thermal vibrations

of the ions about their equilibrium positions, the ion array is not perfectly periodic. These

lattice vibrations are interpreted as quanta called phonons, and the moving electrons are,

in fact, scattered by electron-phonon scattering. As the temperature increases, the number

of phonons created is proportional to temperature and more electrons are scattered by an

increased populations of phonons. Theory predicts that this increased scattering leads to a T"^ temperature dependence of the electrical conductivity. At very low temperatures, where

the population of phonons is nearly zero, defects and voids in the periodic array can still

scatter electrons [4], so real metals cannot have an infinite conductivity even at absolute zero. The model of an electron traveling in a periodic array of thermally agitated positive ions

has been able to correctly explain the electron's large mean-free-paths and the temperature

dependence of the metal's electrical conductivity.

We have very briefly described how quantum mechanics was able to adequately describe

the process of electrical conduction in metals, although we have necessarily left out many

details. The quantum theory of electronic transport that describes the phenomena of electrical conduction in metals is complicated, and the reader who wants a greater understanding

of the quantum-mechanical model of electrical conduction should consult one of the many

solid-state physics books that cover this topic, including those we reference in this paper.

3. Measurement of DC Conductivity

3.1 Measurement System

In order to measure the dc conductivity of various metal alloys, we constructed the measurement system shown in Figure 1. This system is described in [5] and is similar to the

standard test method described in ASTM B 193-02 [6]. It is designed to measure the dc
conductivity of the metal under test from the geometrical dimensions of a cyUndrical metal

rod and the dc current and voltage difference along some length L of the metal specimen.

The equipment necessary for the measurement system includes two digital nanovoltmeters,

a dc power supply, a four-terminal standard resistor, and a two-terminal knife-edge probe.

The dc power supply is connected in series with the metal rod under test and the standard

resistor.

Voltmeter

Voltmeter

]Uh

Metal Rod

Knife-Edge Probe

Calibrated

Resistor

DC Power

Supply

Figure 1: System for measurement of dc conductivity.

3.2 Measurement Theory

In this section we outline the measurement theory used to calculate the dc conductivity

of the metal rod using the measurement system summarized in Section 3.1. We begin by

defining the electrical resistance of a metal rod of uniform cross-section, a value that is a function of the conductivity of the metal and the geometrical dimensions of the metal rod.
In particular, the electrical resistance R across the terminals of the knife-edge probe, whose

contacts with the rod are separated by a distance L is

where A is the cross-sectional area of the metal rod and a is the dc conductivity of the metal

rod. Solving for a, we obtain

Using the definition of resistance R,V — IR, we can rewrite Eq. (8) in terms of the measured

voltage Vm and current /^ seen at the terminals of the knife-edge probe:

Assuming that the current through the metal rod Im is the same as the current through the

calibrated resistor Ir we obtain for the conductivity

L 1 Vr

Note that Eq. (10) is general for any metal specimen that has a uniform cross-section A. In our case, we chose circular-cylindrical metal rods. Therefore, for a circular-cylindrical rod of

diameter d, Eq. (10) reduces to

'^ = ^^k; i^H. (11)

The dc electrical resistivity p of the metal rod is the inverse of the conductivity:

P = ^fir^ [fi-m], (12)

3.3 Measurement Procedure

Before assembling the measurement system, as shown in Figure 1, we allowed the two nanovolt meters and the dc power supply to warm up sufficiently to minimize possible measure- ment drift. Prior to making the conductivity measurement, we cleaned the metal rod and

measured its diameter d, taking many points along the length of the specimen to ensure that

the cross-section is uniform. We then placed the metal sample in the measurement system

and connected the knife-edge probe, making sure that the probe contacts were clean and

set firmly against the metal surface. With the dc power supply providing zero current, we
Table 1: Measured variables and calculated dc conductivity of a stainless steel T17-4P4

alloy at temperature T = 24.8 °C.

Variable Value

L 53.053 mm

d 2.9997 mm

Rr 10 mQ

Vr 1 mV

Vm 0.7622 mV

G 0.985 MS/m

zeroed both the nanovoltmeter connected to the standard resistor and the nanovoltmeter

connected to the knife-edge probe.

With the measurement system now calibrated, we increased the current supplied by the

dc power supply and read the resulting voltages across both the standard resistor V^ and the

knife-edge probe Kn. It is important to collect the voltage data as quickly as possible as the

temperature in the rod begins to increase as soon as the current begins to flow through the

metal rod, ohmically heating it. As the conductivity is a function of temperature, this is an

important issue.

Given the diameter d of the metal rod, the length L between the contacts of the knife-edge

probe, resistance Rr of the standard resistor, and the voltage differences across the standard

resistor K and knife-edge probe Kn, we can calculate the conductivity a of the metal rod

using expression (11).

In Table 1, we show an example of a typical conductivity measurement for a sample of

stainless steel T17-4P4 alloy at a temperature of 24.8 °C.

3.4 Uncertainty Analysis

In this section we identify the major sources of uncertainty and perform an uncertainty

analysis for the calculation of the dc conductivity of a metal rod. The uncertainties in dc

conductivity include the uncertainties Ad in the measured diameter of the metal rod, AL

in the length of the voltage probe, Ai? in the resistance of the calibrated resistor, AK in

the voltage difference across the calibrated resistor, and AKn in the voltage difference across the probe connected to the metal rod. Assuming that each of these sources of uncertainty
Table 2: Uncertainty budget for the measured dc conductivity of T17-4P4 stainless steel

Source of uncertainty Source uncertainty Standard uncertainty in a [S/m

Probe length L 53.053 mm 0.024 mm

Metal rod diameter d 2.9997 mm 0.002 mm

Resistor resistance Rr 10 mQ 0.5 rnn

Resistor voltage K- ImV 0.001 mV

Probe voltage Kn 0.7622 mV 0.002 mV

446 (A)

1313 (A)

49245 (B)

985 (B)

2584 (B)

Calculated dc conductivity

a (9.84 xlO^) [S/m]

Combined standard uncertainty

u(cr) = 0.49 xlO« [S/m]

IS mdependent, the combined root-mean-square standard uncertainty for Act is

Act n(S- + |": +

'da

dRr

ARr +

'da_

dVr

AK +

da

dVr,

AVrr (13)

Since we use Eq. (11) to calculate the conductivity a, we can calculate all the partial

derivatives in Eq. (13)

da 4 1 VC

(14)

(15)

(16)

(17)

and

da 4 1 Vr

dL TTd^RrVm'

da

dd

8 L Vr

nd^RrVj

da 4. L Vr

dRr nd^R'rVm

da 4 L 1 dVr nd^RrVm'

da A L Vr

dVrr 7rd?RrV^ (18)

In Table 3.4 we show the uncertainty budget for stainless steel T17-4P4 metal alloy

considered in the last section. The table lists the various sources of measurement uncertainty,

the value and uncertainty of each measurement variable, and the associated uncertainty in

the dc conductivity a. We also denote whether each uncertainty source is a Type A or Type B uncertainty. Type A uncertainties may be statistically evaluated, while Type B

uncertainties are those that are evaluated using methods other than statistical.
4. DC Conductivity Measurements

4.1 Verification of Measurement System

In order to verify that the dc conductivity measurement system was working properly, we

measured a standard reference material (SRM) acquired from the National Institute of Standards and Technology (NIST). Specifically, we used SRM 1461, a standard reference material

for the measurement of electrical resistivity as a function of temperature . A copy of the SRM

certificate can be found in Appendix A.

Since the electrical conductivity is merely the inverse of the resistivity, SRM 1461 is an

appropriate standard for verifying our measurement system. Figure 2 shows a comparison

between our dc conductivity measurements and the data listed on the SRM certificate. The

certified values for conductivity were sparse near ambient temperature, so we used a polynomial fit to several of the certified data points to compare with our mea^sured conductivities.

Within the temperature range of 15 to 40 °C, our conductivity measurements are in very

good agreement with the certified SRM values.

o

T3CoU

U

Q

1.5

1.4

1.3-

1.2-

1.1 -

l.Qi '

' •100

O New Data • SRM 1461 Polynomial Fit to SRM 1461 Da-«;a

-I I I I 1 I I I I I i_ _1__J L. -50 50

Temperature (C)

100 150

Figure 2: Measurements of dc conductivity on NIST SRM 1461 conc3uctivity standard.

10
Table 3: DC conductivity of various metal alloys at 23 to 25 °C.

Metal alloy Conductivity [MS/m

Sample 1 Sample 2

Copper CIO 100 57.60 57.24

Aluminum 2011 21.11 21.13

Zamek 5 15.91 15.90

Brass C260 15.50 15.50

Alloy steel 4140 4.30 4.29

Stainless steel 430 1.77 1.77

Stainless steel 416 1.53 1.53

NIST SRM 1461 1.21 N/A

Stainless steel 17-4PH 0.98 0.98

Titanium 6A1-4V 0.58 0.58

4.2 Measurements of DC Conductivity

After we verified the conductivity measurement system with the SRM 1621 sample, we

selected nine additional metal alloys having a wide range of conductivities. Based on information provided by law enforcement agencies, a majority of the nine selected metal alloys

measured can be found in weapons such as handguns and knives. The high end of the

conductivity range is represented by an oxygen-free copper alloy, with a conductivity of approximate 57 MS/m, while the low end is represented by a titanium alloy, with a conductivity

of approximate 0.6 MS/m.

For each alloy to be measured, we machined two cylindrical rods 3 mm in diameter gind

150 mm in length. The voltage difference across the knife-edge probe must be sufficient to

read with a digital nanovolt meter. To accomplish this, either the current flowing through

the metal rod must be sufficiently large or the diameter of the rod must be sufficiently small.

Since we want to minimize the heating effects of the current flowing through the rod. we

reduced the specimen's resistance by avoiding a diameter too small, and specified a metal

rod diameter of 3 mm. To avoid any end effects with our knife-edge probe, we specified a metal rod length of 150 mm. approximately three times the length of our longest knife-edge

probe.

Using the measurement system described in Section 3. we measured the dc conductivity

of each sample at ambient temperature (23 to 25 °C). The results of these measurements are

11
oO

u

D

Copper C 10100 Aluminum 201

1

Brass C260

Zainak 5 Alloy SteeU 140

Stainless Steel 430

Stainless Steel 416 NISTSRM 1461

Stainless Steel 17-4 PH

Titanium 6A1-4V

Figure 3: DC conductivity of metal alloys as a function of temperature.

shown in Table 3. Good agreement between measurements on each pair of metal rods was

found for all of the metals characterized.

4.3 Measurements of Variable Temperature DC Conductivity

As mentioned previously, the dc conductivity of metals is inversely proportional to temperature, so we wanted to characterize the metal over the temperature range of interest. By

placing the metal rod under test inside an environmental chamber, we were able to measure

the dc conductivity over a temperature range of 15 to 40 °C. Our particular environmental test chamber had a volume of 0.06 m^. Using a combination of resistance heaters and

chilled gas from a liquid nitrogen dewar, we were able to achieve temperature stability of

approximately 0.5 C.

In order to verify the accuracy of the temperature-dependent conductivity measurements,

we first measured the sample of NIST SRM 1461 stainless steel over a temperature range of 15

to 40 °C. The results shown in Figure 2 agree well with the certified SRM data. After we had

verified the system, we proceeded to measure the remaining metal alloys we had previously

measured at ambient temperature. In Figure 3 we show the temperature-dependent results

for dc conductivity for all 10 metal alloys. As expected, we observed a very small, but

detectable, decrease in the dc conductivity as the temperature was increased.

12
5. Conclusion

In this publication we described a technique for accurately measuring the dc conductivity

of metals. Using a relatively simple measurement system composed of two digital nanovolt

meters, a dc power supply, and a standard resistor, we measured dc conductivities of cylindrical metal rods that ranged from 0.06 x 10^ to 5.8 x 10^ S/m. We derived an equation for

calculating the conductivity of cylindrical metal rods and developed an uncertainty analysis.

After verification of the measurement system with a NIST Standard Reference Material,

we measured nine additional metal alloys that had a wide range of conductivities. In addition to measuring dc conductivity at ambient temperatures, we measured each of the ten

metal alloys over a temperature range of 15 to 40 ° C. These data showed that conductivity

decreased slightly with temperature, as expected.

Special thanks to George Free who developed the measurement system for this research.

Funding for this research was provided by the National Institute of Justice through the

Office of Law Enforcement Standards at the National Institute of Standards and Technology

13
6. References

[1] N.W. Ashcroft and N.D. Mermin, Solid State Physics, W.B. Saunders Company,

Philadelphia, 1976.

[2] B. Donovan, Elementary Theory of Metals, The International Encyclopedia of Physical

Chemistry and Chemical Physics, Pergamon Press, Oxford, 1967.

[3] J.S. Blakemore, Solid State Physics, W.B. Saunders Company, Philadelphia, 1974.

[4] C. Kittel, Introduction to Solid State Physics, John Wiley and Sons, Inc., New York,

1996.

[5] G. Free, "High Accuracy Conductivity Measurements in Non-Ferrous Metals," STP 722,

Americal Society for Testing and Materials, pp. 121, February, 1981.

[6] Standard Test Method for Resistivity of Electrical Conductor Materials, ASTM B 193-02

Standard, ASTM International, West Conshohocken, PA, USA 2002.

14
Appendix A. Certificate for SRM 1461

This appendix contains a copy of the NIST SRM certificate tabulating the values of electrical

resistivity as a function of temperature for the SRM 1461 sample we used for verification of our measurement system.

15
L'. S OtpjnnwtH of CammcKe

Rational ^ureau of ^inndnvdB

fiertifitatc

Standard Reference Materials

1460, 1461, and 1462

Austenitic Stainless Steel Thermal Conductivity (>)

and Electrical Resistivity (o) as a Function

of Temperature from 2 to 1200 K

J. G. Must and A. B. Lankford

These Standard Reference Materials (SRM's) areio be uKd in calibrating methods for measunng thermal conductivity and electrical resuiivity. They are available in rod form. SRM 1460 is 0.64 cm in diametcn SRM 1461 is 1.27 cm in diameter; and 1462 is 3.4 cm in diameter. All rods are SO cm in length.

T(K) X(Wm''K'') p (nAm) T{K) X(W-n>''K:"') p{nnm)

50 6. OS 599 2 0.152 593 60 6.98 606

3 .249 593 70 7,72 613 4 352 593 &0 8.34 622

S .462 594 90 8.85 630 6 .575 594 100 9.30 639

7 .693 594 150 JO. 94 683

S .814 594 200 1120 724 9 .938 594 250 13.31 767

10 1.064 594 300 14.32 810 U 1.323 594 400 16.16 885

14 1.588 594 50O 17.78 944

16 t.8S8 593 600 19-23 997

IS 2.132 593 70O 20.54 1045 20 2.407 593 800 21.75 1088

25 3.092 592 900 22.86 1127 30 3.763 592 1000 23.90 1162

35 4.404 593 1100 24.86 1197 40 S.OI 595 1200 25.77 1234 45 5.57 597

The technical and support aspecU involved in the preparation, certification, and issuance of this Standard Reference

Material were coordinated through the OfTice of Standard Reference Materials by Lee J. Kicffer.

Washington, DC 20234 Stanley D. Rasberry, Chief May 14. 1984 Office of Standard Reference Materials (Revision of Certificates dated 12.11-74, 3-5-75, and 1-17-79)

(over)

16
Me&surernetiu

A. Before 1979

Rased on low-temperaiure (b«low ambient) thertoa] conductivity, electrical rejijtivity, and thcrraopower mcaiure- ments on three specimens; liquid helium and ice-point electrical resistivity meaiureEnenta on twenty specimens: and

other characteriration data such as composition, hardness, density, and grain size [1], the homogeneity of this lot of

austenitic stainless steel was determined to be excellent. These reeasurements indicated that the effect of material vanabitity on thermal conductivity and electrical resistivity is no larger than ±1%.

High temperature (above ambient) data, reported by Fitzer[2] as a result of the AFML-AGARD (Air Force Materials Laboratory. Dayton. Ohio-Advisory Group for Aerospace Research and Development. NATO) reference program, form the basisforextendingthetemperaturerangeof thisSRMto 1200IC. These data have been analyzed and correlated with the low temperature data (I] to obtain the certified values.

B. After 1979

These SRM's were used in an international round-robin study of thermal and electrical properties under the auspices of the Task Group on Thermophysical Profwrlies of CODATA (Committee on Dau for Science and Technology). As a consequence of this cooperative program, a considerable quantity of new data and information were obtained [3]. The

certified values are changed slightly frotn the previous values, however, they are wiihio the previously reported

uncertainty band except in the vicinity of 7 K. The estimated uncertainties of the thermal conductivity data, including material variability, are: 2% belav 100 K.

incrcasingto 3% at ambient temperature, and 5% above ambient. Tbeestimated uncertainties ofthe electrical resistivity data, including material variability, are: 1% below ambient and 2% above ambient temperature. The certified values are

corrected for thermal expansion. The chemical composition is given for information only: Fe 62.0 wt. % Mo 1.2 wt. %

Ni 20.2 Si 0.2« Cr 16.2 C <0,0t

The density is 8.007 ± 0.002 gmcm"'

[1] Hus(, J.G, and Giarratano, P.J., Standard Refcrenoe Material*: Thermal Conductivity and Electrical Resistivity Standard Reference Materials: Austenitic Stainleu Steel. SRM's 115 and 798, from 4 to 1200 K, Nat. Bur. Stand.

Special Publication 260-46 (1975).

(2] Fitzer, E., Thermophysical Properties of Solid Materials, Advisory Report 12 (1967); Advisory Repon 38 (1972); Report 606 (1972), AGARD. NATO, Franee.

[3] Hust, J.G.. and Lankford, A.B.. Update of Thermal Conductivity and Electrical Resistivity SRM's of Electrolytic Iron. Tungsten, and Suintess Steel, Nat. Bur. SUnd. Special Publication 260-90 (1984).

17



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Technical Notes—Studies or reports which are complete in themselves but restrictive in their treatment of a subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of

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Voluntary Product Standards—Developed under procedures published by the Department of

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understanding of the characteristics of the products. NIST administers this program in support of the

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