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NBS SPECIAL PUBLICATION 260-50

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards

Standard Reference Materials:

THERMAL CONDUCTIVITY AND

ELECTRICAL RESISTIVITY

STANDARD REFERENCE MATERIALS:

ELECTROLYTIC IR0N,SRM's 734 AND 797

FROM 4 TO 1000 K

100

.U.57

WIS

L2-
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards 1 was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology

and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau consists of the Institute for Basic Standards, the Institute for Materials Research, the Institute for Applied Technology,

the Institute for Computer Sciences and Technology, and the Office for Information Programs.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United

States of a complete and consistent system of physical measurement; coordinates that system

with measurement systems of other nations; and furnishes essential services leading to accurate and uniform physical measurements throughout the Nation's scientific community, industry, and commerce. The Institute consists of a Center for Radiation Research, an Office of Measurement Services and the following divisions: Applied Mathematics — Electricity — Mechanics — Heat — Optical Physics — Nuclear

Sciences 2 — Applied Radiation 2 — Quantum Electronics 3 — Electromagnetics 3 — Time

and Frequency 5 — Laboratory Astrophysics 3 — Cryogenics 3. THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to improved methods of measurement, standards, and data on the properties of well-characterized

materials needed by industry, commerce, educational institutions, and Government; provides

advisory and research services to other Government agencies; and develops, produces, and

distributes standard reference materials. The Institute consists of the Office of Standard

Reference Materials and the following divisions: Analytical Chemistry — Polymers — Metallurgy — Inorganic Materials — Reactor

Radiation — Physical Chemistry.

THE INSTITUTE FOR APPLIED TECHNOLOGY provides technical services to promote

the use of available technology and to facilitate technological innovation in industry and Government; cooperates with public and private organizations leading to the development of

technological standards (including mandatory safety standards), codes and methods of test; and provides technical advice and services to Government agencies upon request. The Institute consists of a Center for Building Technology and the following divisions and offices: Engineering and Product Standards — Weights and Measures — Invention and Innovation — Product Evaluation Technology — Electronic Technology — Technical Analysis — Measurement Engineering — Structures, Materials, and Life Safety 4 — Building

Environment 4 — Technical Evaluation and Application 4 — Fire Technology.

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts research and provides technical services designed to aid Government agencies in improving cost effec- tiveness in the conduct of their programs through the selection, acquisition, and effective

utilization of automatic data processing equipment; and serves as the principal focus within

the executive branch for the development of Federal standards for automatic data processing

equipment, techniques, and computer languages. The Institute consists of the following

divisions: Computer Services — Systems and Software — Computer Systems Engineering — Information Technology.

THE OFFICE FOR INFORMATION PROGRAMS promotes optimum dissemination and

accessibility of scientific information generated within NBS and other agencies of the Federal Government; promotes the development of the National Standard Reference Data System and

a system of information analysis centers dealing with the broader aspects of the National Measurement System; provides appropriate services to ensure that the NBS staff has optimum

accessibility to the scientific information of the world. The Office consists of the following

organizational units: Office of Standard Reference Data — Office of Information Activities — Office of Technical

Publications — Library — Office of International Relations.

1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted; mailing address Washington, D.C. 20234.

2 Part of the Center for Radiation Research.

3 Located at Boulder, Colorado 80302.

* Part of the Center for Building Technology.
BUREAU Of STANDARDS

IN 1 9 1975

Standard Reference Materials:

r/^oTHERMAL CONDUCTIVITY AND ELECTRICAL RESISTIVITY

STANDARD REFERENCE MATERIALS: ELECTROLYTIC IRON

! ' SRM's 734 AND 797 FROM 4 TO 1000 K

" "

I J. G. Hust and P. J. Ciarratano

I

Cryogenics Division

Institute for Basic Standards

National Bureau of Standards

Boulder, Colorado 80302

U.S. DEPARTMENT OF COMMERCE, Rogers C.B. Morton, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

Issued June 1975
Library of Congress Cataloging in Publication Data

Hust, Jerome G. Thermal Conductivity and Electrical Resistivity. (Standard Reference Materials) (NBS Special Publication;

260-50) Bibliography: p. Supt. of Docs. No.: C 13.10:260-50

1. Electrolytic Iron—Thermal Properties. 2. Electrolytic Iron

Electric Properties. I. Giarratano, P. J., joint author. II. Title.

III. Series: United States. National Bureau of Standards. Stand- ard Reference Materials. IV. Series: United States. National Bureau of Standards. Special Publication; 260-50. QC100.U57 No. 260-50 [TN693.I7] 389'.08s [620.1'7'96] 74-619117

National Bureau of Standards Special Publication 260-50

Nat. Bur. Stand. (U.S.), Spec. Publ. 260-50, 41 pages (June 1975) CODEJV: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1975 For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402

er by SD Catalog No. C13.10:260-50). Price $1.00 (Add 25 percent additional for other than U.S. mailm;
PREFACE

Standard Reference Materials (SRM's) as defined by the

National Bureau of Standards are "well-characterized materials, produced in quantity, that calibrate a measurement

system to assure compatibility of measurement in the nation."

SRM's are widely used as primary standards in many diverse

fields in science, industry, and technology, both within the

United States and throughout the world. In many industries

traceability of their quality control process to the national

measurement system is carried out through the mechanism and

use of SRM's. For many of the nation's scientists and technologists it is therefore of more than passing interest to

know the details of the measurements made at NBS in arriving

at the certified values of the SRM's produced. An NBS series

of papers, of which this publication is a member, called the

NBS Special Publication - 260 Series is reserved for this

pur po s e .

This 260 Series is dedicated to the dissemination of

information on all phases of the preparation, measurement,

and certification of NBS-SRM's. In general, much more detail will be found in these papers than is generally allowed,

or desirable, in scientific journal articles. This enables

the user to assess the validity and accuracy of the measurement processes employed, to judge the statistical analysis,

and to learn details of techniques and methods utilized for

work entailing the greatest care and accuracy. It is also

hoped that these papers will provide sufficient additional

information not found on the c er t if i c a t e . s o that new applications in diverse fields not foreseen at the time the SRM

was originally issued will be sought and found.

Inquiries concerning the technical content of this

paper should be directed to the author(s). Other questions

concerned with the availability, delivery, price, and so

forth will receive prompt attention from:

Office of Standard Reference Materials

National Bureau of Standards

Washington, D.C. 20234

J. Paul Cali, Chief

Office of Standard Reference Materials

iii
OTHER NBS PUBLICATIONS IN THIS SERIES

NBS Spec. Publ. 260, Standard Reference Mate- NBS Misc. Pnbl. 260-12, Standard Reference

rials: 1973 Catalog, April 1973, $1.25.* Materials: Homogeneity Characterization of

NBS Misc. Publ. 260-1, Standard Reference Ma- NBS Spectrometric Standards III: White Cast

terials: Preparation of NBS White Cast Iron Iron and Stainless Steel Powder Compact,

Spectrochemical Standards, June 1964. COM September 1966. NBS Misc. Publ 260-12 **' 74-11061.** NBS Misc. Publ. 260-13, Standard Reference

NBS Misc. Publ. 260-2, Standard Reference Ma- Materials: Mossbauer Spectroscopy Standard

terials: Preparation of NBS Copper-Base. for the Chemical Shift of Iron .Compounds,

Spectrochemical Standards, October 1964. July 1967. NBS Misc. Publ. 260-13 ** COM 74-11063.** NBS Misc. Publ. 260-14, Standard Reference

NBS Misc. Publ. 260-3, Standard Reference Ma- Materials: Determination of Oxygen in Ferterials: Metallographic Characterization of an rous Materials - SRM 1090, 1091, and 1092

NBS Spectrometric Low-Alloy Steel Stand- September 1966. NBS Misc. Publ 260-14 **

ard, October 1964.COM 74-11060.** NBS Misc. Publ. 260-15, Standard Reference

NBS Misc. Publ. 260-4, Standard Reference Ma- Materials: Recommended Method of Use of

terials: Sources of Information on Standard Standard Light-Sensitive Paper for CalibratReference Materials, February 1965. COM ing Carbon Arcs Used in Testing Textiles for

74-11059.** Colorfastness to Light, June 1967. (Replaced

NBS Misc. Publ. 260-5, Standard Reference Ma- by Spec. Publ. 260-41.)

terials: Accuracy of Solution X-Ray Spectro- NB^ g publ 26Q 16 Standard Reference Z

etTu

C^tn ^rS Copper-Base Alloys,

Materialg: Homogeneity Characterization of

,oc m 2 ,i c

( i 1

PD

nf

)- M NBS Spectrometric Standards IV: Prepara- NBS Misc Publ. 260-6, Standard Reference Ma- tion

^d Mi be Characterization of

terials: Methods for the Chemical Analysis of W. 2Q% Mo M Fabricated by Powder

White Cast Iron Standards, July 1965. COM Metallurgical Methods, January 1969. COM

74-11068.** 74-1106^**

NBS Misc. Publ. 260-7, Standard Reference Ma- NBS g publ 26017 Standard Reference

terials:^Methods for the Chemical Analysis of Materials: Boric Acid . Atopic and Assay NBS Copper-Base^ petrochemical Stand- Standard Reference Materials, February

ards, October 1965. COM 74-11067.** 1970 65 cents * NBS Misc. Publ. 260-8 Standard Reference Ma- NBg g

' puW/ 26Q_ 18 Standard Reference

terials: Analysis of Uranium Concentrates at Materials; Calibration of NBS Secondary

?96 IcOM 74 Tl066°**

Cm Standard Ma^etic TaP

C (C °mPUter AmPH" NBS Mis'c. Publ. 260-9, Standard Reference Ma- *ude *

efTnc*> ^^

J^S"*TM

Tap

f,

. , ti i/- t• /»*, - I tt , . Al Amplitude Measurement Process A,

terials: Half Lives ot Materials Used in the AT

1

, in^n /c c n l.i o^r> on \ n • , 0j_ , , „ r n/r x

• 1 November 1969. (See Spec. Publ. 260-29.)

Preparation 01 Standard Reference Materials , IDC c r, , , 0V n in r

c . j 1 D s

- i T

. L „ ,. ^ tvt i j t j 1 NBS Spec. Publ. 260-19, Standard Reference

01 Nineteen Radioactive Nuclides Issued by . r . , A ,

. , T . , , . 1 -jy-r . , „ p j j tvt

" i_ Materials: Analysis of lnterlaboratorv Measthe National Bureau 01 Standards, November . A. \r d t n u

1965 COM 74 11065 ** urements on the Vapor Pressure ot Gold

NBS Misc Publ 260 10 Standard Reference

(Certification of Standard Reference Material

iiDo iviisc iujjj.. iuu-iu, oidiiudiu ixcici ciicc Tanuar 1970 PB 190071 **

Materials: Homogeneity Characterization. on ms ^JTM^. 260-21, Standard Reference

NBS Spectrometric Standards 11: Cartridge , T . r . , A ,

. T . , , . »

„ 1 y . „ 0i , „ , micr Materials: Analysis ot Interlaboratory Meas- ^

TM*hZ~tl y ' DeCCmber 1965- urements on the Vapor Pressures of Cad-

»«• I* ,, 11 o j , nr mium an(i Si,vei% January 1971. COM

NBS Misc. Publ. 260-11, Standard Reference ^

11359 **

Materials: Viscosity of a Standard Lead-Silica

Glass, November 1966. NBS Misc. Publ.

260-10.**

iv
NBS Spec. Publ. 260-22, Standard Reference

Materials: Homogeneity Characterization of

Fe-3Si Alloy, February 1971. COM

74-11357**

NBS Spec. Publ. 260-23, Standard Reference

Materials: Viscosity of a Standard Borosili- cate Glass, December 1970. 25 cents.*

NBS Spec. Publ. 260-24, Standard Reference

Materials: Comparison of Redox Standards,

January 1972. $1.*

NBS Spec. Publ. 260-25, Standard Reference

Materials: A standard Reference Material

Containing Nominally Four Percent Austenite, February 1971. COM 74-11356.**

NBS Spec. Publ. 260-26, Standard Reference

Materials: National Bureau of Standards-U.S.

Steel Corporation Joint Program for Determining Oxygen and Nitrogen in Steel, February 1971. 50 cents.*

NBS Spec. Publ. 260-27, Standard Reference

Materials: Uranium Isotopic Standard Reference Materials, April 1971. COM

74-11358.**

NBS Spec. Publ. 260-28, Standard Reference

Materials: Preparation and Evaluation of

SRM's 481 and 482 Gold-Silver and GoldCopper Alloys for Microanalysis, August

1971. COM 71-50365.**

NBS Spec. Publ. 260-29, Standard Reference

Materials: Calibration of NBS Secondary

Standard Magnetic Tape (Computer Amplitude Reference) Using the Reference Tape

Amplitude Measurement "Process A-Modcl

2," June 1971. COM 71-50282.**

NBS Spec. Publ. 260-30, Standard Reference

Materials: Standard Samples Issued in the

USSR (A Translation from the Russian),

June 1971. COM 71-50283.**

NBS Spec. Publ. 260-31, Standard Reference

Materials: Thermal Conductivity of Electrolytic Iron SRM 734 from 4 to 300 K, November 1971. COM 71-50563.**

NBS Spec. Publ. 260-32, Standard Reference

Materials: Standard Quartz Cuvettes For

High Accuracy Spectrophotometry. December 1973. 55 cents.*

NBS Spec. Publ. 260-33, Standard Reference

Materials: Comparison of Original and Supplemental SRM 705, Narrow Molecular

Weight Distribution Polystyrene, H. L. Wagner, May 1972. COM 72-50526.**

NBS Spec. Publ. 260-34, Standard Reference

Materials: Thermoelectric Voltage, April

1972. COM 72-50371.**

NBS Spec. Publ. 260-35, Standard Reference

Materials: Thermal Conductivity of Austenitic Stainless Steel, SRM 735 from 5 to 280 K, April 1972. 35 cents.*

NBS Spec. Publ. 260-36, Standard Reference

Materials: A Referee Method for the Determination of Calcium in Serum. SRM 915,

May 1972. COM 72-50527.**

NBS Spec. Publ. 260-37, Standard Reference

Materials: Methods of Analysis of NBS Clay

Standards, June 1972. COM 72-50692.**

NBS Spec. Publ. 260-38, Standard Reference

Materials: Preparation and Calibration of

Standards of Spectral Specular Reflectance,

May 1972. 60 cents.*

NBS Spec. Publ. 260-39, Standard Reference

Materials: The Eddy Current Decay Method

for Resistivity Characterization of HighPurity Metals, May 1972. 55 cents.*

NBS Spec. Publ. 260-40, Standard Reference

Materials: Selection of Thermal Analysis

Temperature Standards Through a Cooperative Study (SRM 758, 759, 760), August

1972. 65 cents.*

NBS Spec. Publ. 260-41, Standard Reference

Materials: Use of Standard Light-Sensitive

Paper for Calibrating -Carbon Arcs used in Testing Textiles for Colorfastness to Light,

August 1972. COM 72-50775.**

NBS Spec. Publ. 260-42, Standard Reference

Materials: The Characterization of Linear

Polyethylene, SRM 1475, September 1972.

45 cents.*

NBS Spec. Publ. 260-43, Standard Reference

Materials: Preparation and Homogeneity

Characterization of an Austenitic Iron-Chromium-Nickel Alloy, November 1972.

45 cents.*

NBS Spec. Publ. 260-44, Standard Reference

Materials: Preparation and Use of Superconductive Fixed Point Devices, SRM 767,

December 1972. 75 cents.*

NBS Spec. Publ. 260-45, Standard Reference

Materials: Powdered Lead-Based Paint, SRM

1579, March 1973. COM 73-50226.**

v
NBS Spec. Publ. 260-46, Standard Reference

Materials: Thermal Conductivity and Electrical Resistivity Standard Reference Materials: Austenitic Stainless Steel, SRM's 735

and 798, from 4 to 1200 K. (In press)

NBS Spec. Publ. 260-47, Standard Reference

Materials: Electrical Resistivity of Electrolytic Iron, SRM 797, and Austenitic Stainless

Steel, SRM 798, from 5 to 280K, February

1974. 55 cents.*

NBS Spec. Publ. 260-48, Standard Reference

Materials: Description and Use of Precision

Thermometers for the Clinical Laboratory,

SRM 933 and SRM 934, May 1974. 60

cents.*

NBS Spec. Publ. 260-49, Standard Reference

Materials: Calibrated Glass Standards for Fission Track Use, November 1974. 75 cents.*

NBS Spec. Publ. 260-50, Standard Reference

Materials: Thermal Conductivity and Electrical Resistivity Standard Reference Materials: Electrolytic Iron, SRM's 734 and 797

from 4 to 1000K (in press).

*Send order with remittance to: Superintendent of Documents, U.S. Government Printing Office,

Washington, D.C. 20402. Remittance from foreign countries should include an additional one- fourth of the purchase price for postage.

**May be ordered from: National Technical Information Services (NTIS), Springfield, Virginia

22151.

vi
CONTENTS

Page

1. Introduction 2

2. Historical Review 4

2.1 Early Efforts 4

2.2 Iron 4

2.3 NBS, Washington Efforts 5

2.4 NBS, Boulder Efforts 5 2.5 AFML-AGARD Project

.

5

3. SRM Selection Criteria 6

4. Material Characterization 7 4.1 Electrical Resistivity Characterization 7 4.2 Other Characterization Data 11

5. Apparatus and Measurements 13

5.1 Low-Temperature (below ambient) Measurements 13

5.2 High-Temperature (above ambient) Measurements .... 14

6. Data Analysis (Selection of Best Values) 15

7. Discussion 23

8. Summary 29

9. Acknowledgments 30

10. References 31

vii
LIST OF FIGURES

Figure Page

1. Thermal conductivity of NBS electrolytic iron, ORNL

high-purity iron, and ingot iron above 100 K 16

2. Electrical resistivity of NBS electrolytic iron, ORNL

high-purity iron, and ingot iron above 100 K 17

3. Lorenz ratio of NBS electrolytic iron, ORNL high-purity

iron, and ingot iron above 100 K 18

4. Intrinsic electrical resistivity of NBS electrolytic

iron, ORNL high-purity iron, and ingot iron above 100 K. . 20

5. Deviations of intrinsic electrical resistivity data for

iron from p . = aTn + bT 21

x

6. Thermopower of NBS electrolytic iron, ORNL high-purity

iron, and ingot iron ( above 100 K 22

7. Recommended electrical resistivity values for NBS

electrolytic iron (SRM 797) 24

8. Recommended thermal conductivity values for NBS

electrolytic iron (SRM 734) 27

9. Lorenz ratio values of NBS electrolytic iron 28

LIST OF TABLES

Table Page

1. Residual resistivity ratios of various specimens of

NBS electrolytic iron 10

2. Chemical composition of NBS electrolytic iron and

ORNL high-purity iron and typical values for ingot iron . . 12

3. Electrical resistivity, SRM 797, thermal conductivity,

SRM 734, and Lorenz ratio values for NBS electrolytic

iron. . . 25

viii
Thermal Conductivity and Electrical Resistivity

Standard Reference Materials: Electrolytic Iron,

SRM's 734 and 797 from 4 to 1000 K.

J. G. Hust and P. J. Giarratano

Cryogenics Division

NBS - Institute for Basic Standards

Boulder, Colorado, 80302

Abstract

A historical review of the development of Standard Reference

Materials, SRM's, is given and selection criteria of SRM's are listed.

Thermal conductivity and electrical resistivity data for electrolytic

iron and similar irons are compiled, analyzed, and correlated. Recommended values of thermal conductivity and electrical resistivity for

electrolytic iron, SRM's 734 and 797, are presented for the range

4 to 1000 K. These values are based on NBS measurements up to 280 K

and on measurements by Oak Ridge National Laboratory on a similar iron

above 280 K. The average uncertainty of the thermal conductivity values

below ambient is 1.5% and 3% above ambient. The corresponding uncertainties in electrical resistivity are 1% and 2%.

Key Words: Electrical resistivity; electrolytic iron; high temperature;

iron; Lorenz ratio; low temperature; standard reference material; thermal

conductivity; thermopower.

1
1. Introduction

Design and development engineers continually demand thermal and

electrical property data of technically important materials. Often

these data are not in the published literature and immediate measurements must be performed. Since only a handful of laboratories have the

proven expertise to make such measurements, usually they are performed

by inexperienced personnel using unproven apparatus. The results, as can be seen from the literature, exhibit excessive scatter; 50% differences are commonplace. In such situations, Standard Reference Materials,

SRM's, are invaluable to ascertain the accuracy of the engineering measurements. Currently, an inaccuracy of 10% is allowable for most engineering thermal property data, and therefore, SRM's for engineering applications need to be established with an uncertainty no larger than about 5%.

A few research laboratories performing thermal and electrical measurements are obtaining data with uncertainties at the state-of-the-art

level, 1% for thermal conductivity and lower for electrical resistivity.

SRM's for use at such laboratories must be correspondingly more accurate

and may indeed be possible but have not yet been established.

Considerable effort has been directed toward the development of

suitable thermophysical SRM's*, over a period of many years, with limited

success. This lack of success may be due, in part, to the tacit assumption

that SRM data must be accurate to state-of-the-measurement-art to be useful. There are several reasons why the achievement of thermal and electrical property SRM's with certified inaccuracies of less than 1% is

extremely difficult. The principal reason is that material variability,

generally, causes property variations of greater than 1% even with the

most up-to-date production control techniques. The effects of material

variability lead to the consideration of three categories of calibration

materials and three concomitant certification inaccuracies: (1) A

characterized type of material, e.g., copper, gold, iron etc. Based on

past experience it appears that inaccuracies of 5-10% can be expected.

(2) A characterized specific lot of a given type of material, e.g.,

austenitic stainless steel, SRM 735, or electrolytic iron

? SRM 734. Data

uncertainties of one percent appear to be near the lower limit of current

production control techniques. (3) Characterized specimens of material.

At first glance, it may be thought that the latter SRM's would be invariant; but it is known that the thermal and electrical properties of some specimens change spontaneously with time, aging effects, and are also dependent on their thermal and mechanical histories. These effects are especially significant at low temperatures especially for highly

* The term SRM is used here in a broad sense to denote any material or specimen that is to serve as a calibration standard. The term, as coined

by the Office of Standard Reference Materials, generally implies a specific lot of material prepared under strict control and subsequently characterized for chemical composition and homogeneity.

2
purified materials. Appropriately chosen well-characterized specimens, handled with care to avoid physical and chemical changes, and frequently reexamined to detect changes, presently represent the only means

to achieve accuracies in the state-of-the-measurement-art range. This

is the basis of round-robin type measurements used by standardizing laboratories for state-of-the-art apparatus intercomparisons (see, for

example, Laubitz and McElroy [1]). Category (2) is considered to be the

most cost-effective to satisfy engineering needs and, to a lesser extent,

the needs of standards laboratories. It is also the philosophical basis

of the Office of Standard Reference Materials, National Bureau of Standards.

This report is a result of a program to establish several thermal

and electrical conductivity metal SRM's with conductivities ranging from

pure metals (high conductivity) to structural materials (low conductivity)

Plans are being formulated to extend this program to insulating materials

and dielectric solids as well. The current effort will result in two

additional reports: one on tungsten (high conductivity, 4 to 3000 K)

and another on austenitic stainless steel (low conductivity, 4 to 1200 K)

The material reported on here, electrolytic iron, is in the medium-tohigh conductivity range.

This paper reviews the historical development of thermal conductivity

SRM's. A listing is given of selection criteria for SRM's and a justification is presented for the establishment of both engineering and standards

laboratory SRM's. Data are compiled and best values are selected to establish electrolytic iron as electrical resistivity and thermal conductivity

SRM's 797 and 734, respectively. As discussed later, thermal conductivity

and electrical resistivity data have been obtained to certify these SRM's over the range 4 to 1000 K to well within engineering accuracy. This

material appears to have the qualities of an excellent SRM. An adequate

supply of this material exists to insure measurement compatibility among

laboratories for about ten years.

The following historical review of SRM efforts is presented to

indicate the relatively large amount of research that has been conducted,

compared to the few thermophysical SRM's that have been officially established. It is this divergence between expended efforts and concrete

results that has prompted us to establish potentially useful SRM's, at

what may seem to some as a premature phase of the work. Based on past

experience, it appears that if this is not done, a vast amount of research

is lost. Not because the data are lost, but rather, because the stock of

material, on which the research was performed, is lost. This consideration also points out the significance of continuity in SRM projects.

*This electrolytic iron is a specific lot of iron produced for NBS to

maximize homogeneity. Throughout this paper it is referred to as NBS

electrolytic iron as it is the basis for several SRM's distributed by

NBS,0SRM.

3
2. Historical Review

2.1 Early Efforts

Thermophysical property reference material investigations began,

for all practical purposes in the 1930 's with the work of R. W. Powell

at the National Physical Laboratory (NPL) , Teddington, England [2] on iron and Van Dusen and Shelton at NBS [3] on lead. These efforts were

successful in that they resulted in frequently used reference materials

of thermal conductivity. Powell's work resulted in the establishment

of ingot iron* (category 1) as a standard, which is still being used

today. Lucks [4] recently reviewed the massive amount of work that

has been done on this material and recommended the continued use of ingot

iron as a reference material. Van Dusen and Shelton' s work resulted

in an unofficial lead standard based on a well-characterized lot of pure

lead (category 2) distributed by NBS as a freezing point standard.

2 . 2 Iron

Since the 1930 's reference material investigations have been sporadic

with notable efforts by researchers from the NBS (National Bureau of

Standards, U.S.), NPL (National Physical Laboratory, England), ORNL

(Oak Ridge National Laboratory, Tennessee), BMI (Battelle Memorial

Institute, Ohio) , and AFML (Air Force Materials Laboratory, Ohio) . The

material that has been the subject of the most extensive investigations

is ingot iron. Renewed interest in this material was spurred by the

round-robint experiments initiated by C. F. Lucks of Battelle Memorial

Institute during 1959. Twenty-four laboratories requested and received

the round-robin material for measurements. Data from eight laboratories

were ultimately reported and compiled by Lucks [4]. These data are on specimens obtained from a single lot of ingot iron. The literature, (see

Lucks) however, contains data on a total of eleven distinct lots of ingot

iron. Lucks [4] has shown that ingot iron is an acceptable reference

material at temperatures from about 100 K to 1000 K. In this range, material

variability affects thermal conductivity and electrical resistivity by

about 5%. At higher temperatures, reported variations increase. At

lower temperatures, especially at liquid helium temperatures, variations

of 10% have been reported on a single 30 cm long rod by Hust et al [5,6].

Electrolytic iron, SRM 734, was established as a low-temperature standard

by Hust and Sparks [7] because it exhibits relatively small low-temperature variability. Based on their high temperature study of ingot iron

and a high purity iron, Fulkerson et al [8] also concluded that high

purity iron is a more homogeneous and stable SRM.

* The ingot iron used for this purpose is Armco iron produced by Armco

Steel Corporation. The use of trade names of specific products is

essential to the proper understanding of the work presented. Their use

in no way implies any approval, endorsement, or recommendations by NBS.

f The use of the term "round-robin" is different here from that used

earlier where the use of a single specimen was implied; however, this

double meaning is allowed to be consistent with the literature on ingot

iron.

4
2.3 NBS, Washington Efforts

D. R. Flynn of NBS, Washington began a study of potential thermal

conductivity SRM's during the early 1960's. He examined several ceramics*

and alloysf . None of these materials has achieved the status of an SRM.

Descriptions of these efforts appear in the unpublished proceedings of

the early thermal conductivity conferences. Laubitz and Cotnam [9] re- ported that Inconel 702 exhibits transformation effects of several percent in thermal conductivity and recommended against its use as a reference material.

At the 1963 thermal conductivity conference, Robinson and Flynn [10]

presented the results of a survey of thermal conductivity SRM needs.

SRM's with a data uncertainty of 3-5% were in greatest demand. The intended use of SRM's, most often stated, was to check and calibrate apparatus. Needs were indicated for SRM's of conductivities from 0.01 W/mK

to 500 W/mK at temperatures from 4 to 3300 K.

2.4 NBS, Boulder Efforts

R. L. Powell of NBS, Boulder initiated a low-temperature SRM project

during the early 1960's. This project has been continued by the first author

since that time. Materials studied include ingot iron, electrolytic iron,

gold, tungsten, graphite, and stainless steel. As a result of these studies, electrolytic iron and stainless steel have been established as lowtemperature (4 to 280 K) SRM's of electrical resistivity and thermal con- ductivity. Current efforts are directed toward the extension of these to

higher temperature and to establish graphite and tungsten as SRM's at

temperatures up to near 3000 K. It is anticipated that this project will

continue until a sufficiently wide range of conductivities and temperatures

are included to satisfy existing demands for thermophysical SRM's.

2.5 AFML-AGARD Project

Minges [5th Thermal Conductivity Conference, 1965] reported on the

initiation of an AFML sponsored high-temperature reference materials program. This program was divided into two phases. Phase I included the

preliminary selection and characterization of materials as potential

reference materials. Selection criteria were established, dozens of

materials screened, and about 15 were chosen for experimental evaluation.

Phase II included further measurements on those materials selected from

Phase I studies. Arthur D. Little Corp. contracted with AFML to perform

* Pyroceram 9606 and Pyrex 7740 (trade names of Corning Glass Works)

t Inconel 702 (trade name of International Nickel Company, Inc.),

lead, and 60% platinum - 40% rhodium alloy.

5
this study. The results were reported in reference [11]. The materials

of particular interest in Phase II of this program were aluminum oxide,

thorium oxide, tungsten, and graphite.

After partial completion of the AFML program, an international program, principally high-temperature, was initiated under the auspices of

the Advisory Group for Aerospace Research and Development, NATO (AGARD)

E. Fitzer of Karlsruhe University, Germany, directed this program in

close cooperation with the AFML program. The establishment, progress,

and results of this program are described in a series of reports by

Fitzer [12]. Minges has also summarized some of the results on AFMLAGARD programs [13]. The materials, internationally distributed and

measured by numerous laboratories, are: platinum, gold, copper, austenitic

steel alloy, tungsten (both sintered and arc-cast), tantalum - 10%

tungsten alloy, alumina, and graphite.

3. SRM Selection Criteria

The criteria for screening and selecting potentially useful materials

for physical property SRM's are generally well-understood and accepted.

These criteria are not met absolutely by any material, but serve as a guide to determine which materials are most suitable. Some of the more

significant factors are:

1. The material should be homogeneous* and isotropic throughout a

lot. The lot should be large enough to be adequate for at least

a decade and renewable with a minimum of effort.

2. Thermo physical properties should not vary with time and should

be relatively unaffected by the environment of the measurement

apparatus. The material should have chemical stability, thermal

shock resistance, low vapor pressure, and insensitivity to stress.

3. The material should be readily available, machinable, be

relatively inexpensive, and have sufficient strength to be handled

without causing damage.

4. The material should have characteristics similar to the material

to be measured.

* The term homogeneous refers here to the uniformity of the thermophysical property in question. Homogeneity of a thermophysical SRM implies

not only chemical homogeneity, as in chemical composition SRM's, but also

homogeneity of physical characteristics of the material. The parameters

affecting physical property homogeneity are so numerous that detailed

characterization of each is prohibitive. Instead, one often reverts to

aggregate characterization methods, such as by electrical resistivity as discussed later.

6
5. The material should be useful over a wide temperature range.

The electrolytic iron described in this report satisfies these criteria

reasonably well.

4. Material Characterization

The purpose of this work is to establish NBS electrolytic iron as SRM's of thermal conductivity and electrical resistivity at temperatures

from 4 to 1000 K. To support our thesis that this lot of material is

sufficiently homogeneous and the recommended data are accurate to within

the stated uncertainties, we present extensive characterization data.

Since the recommended SRM values for NBS electrolytic iron are based,

in part, on measurements on other irons, characterization data for ingot

iron and ORNL high purity iron [8] are included. The characterization

data for NBS electrolytic iron have been presented previously by

Hust and Sparks [7,14] and in a supplement to Reference [7]. Since these

data are not found in a single source, they are repeated here.

4.1 Electrical Resistivity Characterization

Extensive reliance is placed on electrical resistivity variability

as an indicator of thermal conductivity variability for pure metals. The

justification for this is presented below.

The electrical resistivity, p, and thermal conductivity, X, of

metals are intimately related, especially for pure metals, but also for

alloys to a lesser extent. This relationship exists because in a metal

most of the heat is transported by the electrons. Some heat is also

transported by the lattice vibrations. The total thermal conductivity

is the sum of the electronic, X , and the lattice, X , (the German

e* g

word for lattice is Gitter) components.

X = X + X . (1) e g

In most pure metals X^ is small compared to X^, but in transition metals

X may be as large as 20% of A. , and in some alloys X is much larger

than X^. For pure metals and dilute alloys, the relationship between

p and X at both high and low temperatures is reasonably well described

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

^ = L = 2.443 x 10"8 vV2, (2)

T o where L

q

is the Sommerfeld value of pA./T and T is the temperature. At

intermediate temperatures, large deviations from the WFL law are observed.

For our purposes the ice point is a sufficiently high temperature and

liquid helium is a sufficiently low temperature to satisfy the WFL

law.

7
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 thermal vibrations of the atoms of the lattice. The former mechanism

is usually taken to be 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 scattering is

usually referred to as the residual resistivity, P q

, while the resistivity due to thermal scattering is called the intrinsic resistivity,

p^(T). The total resistivity, p (T) , may be written as the sum of these

two terms.

p(T) = P Q

+ P i (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; consequently, 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 . The temperature at which p (T) becomes constant depends upon the purity

of the sample, but for most materials available at the present time,

the intrinsic resistivity 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, a common procedure is to determine a specimen's

resistance at the ice-point, R ^, anc^ at ^ ^» ^4' aru^ calculate tne

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 perfection, of

the specimen. Since the specimens measured here were generally in the

annealed condition, the RRR value should indicate the effective chemical

purity (electrical purity)

8
As an exercise to show the validity of this statement, we computed

the residual resistivity from the measured chemical composition of NBS

electrolytic iron. Using the specific resistivities listed by Blatt [15],

we obtained a value of 5nQn assuming that all the impurities are in

solution. Since the measured residual resistivity is 4 nQn, the electrical purity is in good agreement with the chemical purity. Thus, we

expect that variations in measured residual resistivity are an excellent

indication of chemical inhomogeneities and physical imperfection variations .

Electrical resistivity variations are accompanied by thermal con- ductivity variations of nearly the same proportion as shown by the WFL

law. Therefore, the determination of residual resistivity or residual

resistivity ratio variability will directly indicate thermal conductivity variability. The measurement of electrical resistivity is, of

course, much easier than the determination of thermal conductivity.

An extensive resistivity variability study was conducted on NBS

electrolytic iron prior to its certification as SRM 734 in 1971. The

objective was to determine if this material could be heat treated in

such manner that the thermal conductivity would be nearly the same

(± 1%) for each specimen. This was achieved with a 2-hour, 1000°C

anneal in either a vacuum or helium atmosphere. The results of this

study were reported as residual resistivity ratios in [ 14 ] and are re- peated in table 1. The ratio given is resistivity at 273.15 K to re- sistivity at 4 K.

Various heat treatments were tried during 1970 to stabilize the

residual resistivity ratio, RRR, of this iron. After an anneal of 500°C

for 1 hour, the ratio increased from 20.11 in the as received condition

to 22.54. Raising the temperature to 1000°C for 2 hours produced rods

which appeared stable at a ratio of 23.33 ± 0.24. The -variation shown

is 2s, where s is the estimated standard deviation, and includes material

and measurement variability. In order to study the possibility of a change in ratio with age, some of the rods were measured after about 50

days and no significant change was detected. At that time, SRM 734 was

established for the range 6 - 280 K with the conclusion that no significant changes would occur with age.

After three years of room temperature aging, a 4% increase in RRR

was found. It is also noted that heating to 400°C for 2-1/2 days changed

the ratio to 24.94 ± 0.26 when the first measurements were made during

1970. However, in 1973 a similar heat treatment produced a much smaller

change (about 1%) . This is not understood but the result of the latter

measurement allows consideration of extending this SRM to higher temperatures. It is to be noted that the above mentioned room temperature aging

effect does not significantly alter the thermal conductivity of SRM 734

9
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fNJ fSJ f\] fNJ

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10
at temperatures above 60 K. At room temperature, the magnitude of the

effect on thermal conductivity over the three year period is only about

0.2% while at 60 K it is about 1%. The full effect, 4%, is seen only at

4 K. This statement is based on the observed changes in electrical re- sistivity at the ice point and at liquid helium temperature. These measurements, reported below as resistivity ratios for convenience, showed

the following: The range of residual resistivities measured for all of

the specimens and various heat treatments is about 30%. The average

residual resistivity ratio for all of these measurements is about 23.

Based on Matthiessen 1 s rule, one would expect the ice point resistivity

range to be about 1-1/2%. The measured ice point resistivity range is

about 3%, which is consistent with the 1-1/2% expected range within the

measurement uncertainty of ± 1%. The average intrinsic resistivity of

NBS electrolytic iron at the ice point is 87 . 1 nfin ± 0.2%.

After performing further anneals to obtain a better understanding

of the aging phenomena, it appears clear that our earlier selected

anneal procedure, although described insufficiently, was proper in that

we obtained the RRR value which is least dependent on heating to temperatures below 800 °C and is, therefore, most stable with time. However,

we were not aware, at the time, of the importance of the cooling rate

of the furnace. At that time, we used a massive furnace which cooled

rather slowly (approximate decay time constant of 6 hours) . With the

smaller furnace (approximate time constant of 3 hours) used in the later

measurements, a hold of at least two hours at 800°C was necessary to

stabilize this iron. After this heat treatment, heating specimens to

intermediate temperatures does not significantly effect the residual

resistivity ratio. These measurements show that SRM 734 can be used

as a thermal conductivity standard with a variability of about 1% if

annealed at 1000°C for 2 hours, cooled to 800°C and held for 2 hours,

and furnace cooled to ambient. The effect of more rapid cooling rates

below 800°C was not investigated.

4.2 Other Characterization Data

The density of electrolytic iron, determined by air and ^water weighings (see Bowman and Schoonover [16]), is 7.867 ± 0.005 g/cm . Rockwell

hardness and grain size are B24 and 0.05 mm, respectively. Grain size was determined by the American Society for Testing and Materials (ASTM)

comparative method. The above data were determined with the material

in the annealed state. The chemical purity of this electrolytic iron

is 99.9+ weight percent Fe. The chemical composition, as certified by

NBS, SRM 1265, is given in table 2, along with typical values for ingot

iron and the high-purity iron measured at Oak Ridge National Laboratory

(ORNL) by Fulkerson et al f8]. The values listed for ingot iron must

be considered typical, since the ingot iron investigated was not a single lot of material, but , rather, many lots as produced over a period

of many years.

11
Table 2. Chemical composition of NBS electrolytic

iron and ORNL high-purity iron and

typical values for ingot iron

Composition (weight percent)

Element NBS electrolytic ORNL high- ingot iron

iron purity iron

Carbon 0.0067 0.003 0.015

Manganese 0.0057 0.028

Phosphorus 0.0025 0.001 0.005

Sulfur 0.0059 0.003 0.025

Silicon 0.0080 <0.01 0.003

Copper 0.0058 <0.001 0.04

Nickel 0.041 <0.01

Chromium 0.0072

Vanadium 0.0006

Molybdenum 0.005

Cobalt 0.007

Titanium 0.0006

Arsenic 0.0002

Aluminum 0.0007 <0.001

Boron 0.00013

Lead 0.00002

- = unknown

12
For comparative purposes other characterization data are presented.

Srain size of ingot iron is about 0.05 mm. Residual resistivity ratio,

°273K^UK' ^aS ran§ec* f°r t*ie vari°us lots from about 9 to 14, compared

to a mean of 23 for NBS electrolytic iron. Hardness of ingot iron is

about Rockwell B40. The high-purity ORNL iron has a reported residual

resistivity ratio of 23, the same as for electrolytic iron. The grain

size of ORNL high-purity iron is significantly larger than either ingot

iron or NBS electrolytic iron. Grain size is undoubtedly dependent on

the previous thermal history of each specimen and may not be a significant

characterization parameter.

5 . Apparatus and Measurements

The intent of this paper is to establish NBS electrolytic iron as SRM's of thermal conductivity and electrical resistivity at temperatures

from 4 to 1000 K. The following sections describe the measurements

resulting in data pertinent to this study. The low-temperature data

originate entirely with NBS , Boulder and the high-temperature data are entirely from the published literature on similar irons.

5.1 Low-Temperature (Below Ambient) Measurements

Thermal conductivity, electrical resistivity, and thermopower measurements were performed with a multiproperty apparatus based on the

axial one-dimensional heat flow (longitudinal) method. The specimen is

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

and a temperature controlled heat sink at the other. The specimen 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.

A detailed description of this apparatus and an error analysis are presented by Hust et al [6], The estimated uncertainties (with 95% confidence) are as follows:

Thermal conductivity: 2.5% at 300 K decreasing to 0.7% at 200 K,

0.7% from 200 K to 50 K, and increasing to 1.5% at 4 K.

Electrical resistivity: 0.25%.

One specimen was measured in the low-temperature apparatus over

the range 4 to 280 K. The data were smoothed using conventional linear

least-squares methods with the following equations:

n . - in\ = Z a. [in T]

i=l

1

m

p = Z b. [in T]

1 L 1=1 1

where X = thermal conductivity, p = electrical resistivity, and T = temperature, which is based on the IPTS-68 scale above 20 K and on the

NBS P2-20 (1965) scale below 20 K. These functions have no theoretical

significance, but are chosen from past experience on the basis of their

13
usefulness for smoothing similar data. The optimum number of parameters

is selected by utilizing orthogonal fitting analysis to avoid either underfitting or overfitting the data. In the first case, excessive oscillations,

or wiggles, may be introduced in the temperature dependence. These equations are used primarily for data analysis and smoothing to within the

accuracy of the data. Because of the form of the raw experimental data,

the extensive number of data points, and the complexity of the data

analysis, the experimental data are not presented here. They are, however, printed in an informal NBS report [17] which may be obtained from

the author. No other data sources exist for temperatures below ambient.

The previously presented fixed-point electrical resistivity characterization data were obtained using a conventional four-terminal apparatus.

5.2 High-Temperature (Above Ambient) Measurements

No high- temperature measurements have been performed on NBS electrolytic iron, per se. However, measurements have been performed extensively

on similar irons at elevated temperatures. In particular, as discussed

earlier in this paper, ingot iron has been measured repeatedly since 1932.

Ingot iron is somewhat less pure than NBS electrolytic iron, (see table 2)

Lucks [4] has recently reviewed the thermal conductivity and electrical

resistivity measurements on ingot iron. Although Lucks' paper does not

include descriptions of the apparatus used for the past measurements, it can be used as a bibliographic source directing the reader to the original

experimental papers. A summarization of these papers must include the

statement : ingot iron has been measured using more different types

of apparatus at more laboratories than any other material

Although the ingot iron data are valuable in establishing reference

data for NBS electrolytic iron, it is fortuitous that data for an iron

almost identical to NBS electrolytic iron has been published by Fulkerson

et al [8]. This data set is especially pertinent since it is the result

of the most extensive single experimental and analytical work on iron

at elevated temperatures and is from workers of proven expertise. This

well characterized, high-purity iron is identified as ORNL in the material

characterization section. Table 2 shows the composition of NBS electrolytic

iron to be between that of ingot iron and the high-purity ORNL iron, but

significantly closer to the latter. Confirmation of this is reinforced

by the agreement of the measured residual resistivities of these irons,

NBS electrolytic iron differs by only 2% from high-purity ORNL iron

and 50% from ingot iron.

Thermal conductivity, electrical resistivity, and thermopower measurements were performed by Fulkerson et al \8] at temperatures from near ambient to above 1200 K with a radial heat flow apparatus. The reported

most probable errors for these data are about 2% for thermal conductivity

and 0.5% for electrical resistivity.

14
6. Data Analysis (Selection of Best Values)

After the establishment of SRM's 734 (thermal conductivity) and

797 (electrical resistivity) for temperatures below ambient, no new

measurements have been reported. Thus no modifications of the previously

recommended reference data are necessary. From 6 to 280 K the recommended values of thermal conductivity are those reported by Hust and

Sparks [7] and the corresponding values of electrical resistivity are

those reported by Hust [14] . These values for SRM's 797 and 734 are listed in table 3.

At temperatures above ambient, the recommended values of electrical

resistivity and thermal conductivity for electrolytic iron are based

on the values reported for high-purity ORNL iron. Ingot iron data are used to reinforce the validity of this selection and to establish probable

error bounds. The following discussion presents the basis of this

selection.

Figures 1 and 2 illustrate the thermal conductivity and electrical

resistivity for NBS electrolytic iron, ORNL high-purity iron, and ingot

iron as reported by the indicated authors. The thermal conductivity of

NBS electrolytic iron is measureably greater than that of ingot iron, 12%

at 100 K and 5% at 300 K. Figure 2 shows that similar differences, but

opposite sign, occur in the electrical resistivities of these irons. It

is also observed from figures 1 and 2 that the reported data for NBS

electrolytic and ORNL high-purity iron are the same to within the reported

uncertainties of the measurements. This is not surprising in view of the

previously mentioned similarities of the compositions and other characterization parameters.

Since iron conducts heat primarily by electrons, one would expect

the Lorenz ratio, pX/T, to be a useful tool for correlating the thermal

and electrical conductivities of these irons. Figure 3 illustrates the

Lorenz ratios above 100 K for these irons. The values plotted are obtained from the total thermal conductivity and, thus, include the lattice

component of conductivity. It is noted that the Lorenz ratios of all

three of these irons agree to within 2% above ambient temperature. The

values for Armco iron are consistently greater than those for the higher

purity irons. In spite of the fact that the 2% difference is near experimental uncertainty, it is believed to indicate a real difference.

Based on the compositions listed in table 2 one would expect the Lorenz

ratio of NBS electrolytic iron to be below that of ingot iron. One

would also expect the Lorenz ratio values for ORNL iron to be slightly

lower than NBS iron. In view of the combined data uncertainties for

these data sets (about 2-3%) , the confirmation of the above predictions

is remarkable.

15
<3>

00

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o

00

o

o

Co

Su

LU +J

CC >> ZD

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=c

d: M

uj u

Q_ CD s:

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1

RE

ZD

u. o

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( ^ _ >1 ^ _WM ) AlIAIIDnONOD !VWci3Hl

16
00 200 400 600 1000

TEMPERATURE (K)

FIGURE 2 - Electrical Resistivity of NBS Electrolytic Iron, ORNL High-Purity Iron, and Ingot Iron above 100 K.

17
1 1 1 o 0

1 1 1 1 1 1

1 1 —

o O I

ron S_ —

u +-> o o +J s- >> Q- o 1 o S

s_

+-> JZ

CTi

t j

<J

QJ J£ oo

LU Z

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o

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1.01

+-> o O

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o

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oo

1

o

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1 1

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o

oo

o

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o

o

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o

o

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o

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18
Additional evidence that these data sets are compatible to within

the stated uncertainties is illustrated in figures 4 and 5. Figure 4

is a plot of the intrinsic electrical resistivities, p^, as obtained

from Matthiessen' s rule,p = p + p.. The value of residual resistivity,

o x

p , used for ingot iron is 10 nf2m, as estimated from the literature cited

by Lucks. The data above ambient were represented with p_^ = aTn + bT

and figure 5 illustrates the differences among the three data sets using

this function as the baseline. The differences are consistent with the

uncertainties of the data. Fulkerson et al f8] have reported increasing absolute resistivity differences between ingot iron and ORNL highpurity iron of about 1% from ambient to 1000 K, i.e., non-Matthiessen'

rule behavior. This may be caused by an increase of impurities in solution for ingot iron as temperature increases, as discussed in the same paper [8]. In any event the effect on the difference between intrinsic

resistivity as obtained for ORNL high-purity iron and NBS electrolytic

iron should be below 1%.

The thermopower of NBS electrolytic iron was reported by Hust and

Sparks [17] at temperatures up to 280 K. Fulkerson et al [8] reported

thermopower of the ORNL high-purity iron and ingot iron above 273 K.

The results, illustrated in figure 6, are in good agreement and again

the values for NBS electrolytic iron are between those for the other two

irons. Thermopower data by Hust et al [6] on ingot iron below 300 K

are in excellent agreement with those published by Fulkerson et al [8].

Since the intrinsic electrical resistivities are in good agreement

as shown in figures 4 and 5, we recommend the high- temperature p^ values

as reference data for NBS electrolytic iron. Smoothed high temperature

intrinsic resistivities were calculated from the equation

p. = aT

n + bT.

l

The parameters a = 6.512 x 10 , n = 2.3438, and b = 0.1965 were obtained

by a least squares fit to the high temperature intrinsic resistivities.

The ice point data on NBS electrolytic iron was used to constrain the

function at 273.15 K. The deviations of this equation from the data

of Fulkerson et al [8] are illustrated in figure 5. Also included in

this plot are the data of Hust [14] above 200 K. Note that this

equation joins with the low-temperature data of Hust [14] at 273 K

but below 273 K the equation diverges rapidly from the three sets of

data. The reader is therefore cautioned not to extrapolate this equation below 273 K. Total resistivities are then obtained by adding the

residual resistivity of NBS electrolytic iron, 3.85 n^m.

19
1 H

I |1

l

1 l 1 1 11

1

CD

—

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—

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+-> —

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tic

Iron)

}NL

High- a

(ID — >> o

o

S-

-t-> c

o

s. a — <J

Ol

ro

LU

-l-> CD

•!-> o

cn

I/O CO c c

:erst to —

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Lucl< o

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o O £ —

I 1 1 1

1 i 1 l 1 1 1 1 *

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of—

o

o

o

o

CO

o

o

o

o

o=3"

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O

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20
s qM o l j . -d/OOI(

21
o

o

o

c: o

o s- s- +-> r- <_> <D

+-> I— O (LI cnC IS> i- CO oc

10CL

"Oc

o

00

00

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C30

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22
These high-temperature data combined with the data of Hust [14] are the recommended values for SRM 797 and are listed in table 3 and

plotted in figure 7. The uncertainty of these values of electrical

resistivity is estimated as 1% below 280 K and 2% above. The electrical

resistivity values listed in table 3 are based on ambient temperature

specimen dimensions, i.e., they are not corrected for thermal expansion.

This is believed to be the most convenient form for the user. To obtain

true resistivity one would increase the resistivity in table 3 linearly

with temperature above ambient. The increase at 1000 K is about 1%.

Thermal conductivity values for NBS electrolytic iron at temperatures

above ambient are obtained directly from the ORNL high purity iron data.

Consideration was given to correcting these data to account for the slight

residual resistivity difference (2%) between the ORNL high-purity and NBS

electrolytic irons. This correction, however, is less than 0.2% above

280 K, which is negligible compared to the uncertainty of the recommended

values (3%) . The recommended thermal conductivities are listed in table 3

and plotted in figure 8. Lorenz ratios as calculated from the recommended

values of electrical resistivity and thermal conductivity are listed in

table 3 and plotted in figure 9.

7. Discussion

The principal factors determining the validity of SRM data are measurement uncertainty and material variability. Measurement uncertainty

is a highly speculative quantity, as evidenced by the fact that most

experimentalists present optimistically low uncertainties for their own

work. The best way to obtain realistic uncertainties is through roundrobin type measurements using apparatus as basically different as possible.

Such programs are expensive and, therefore, not often performed. It is

essential for standardizing laboratories to be involved in such programs

for this forms the basis of essentially all other measurements. SRM's

resulting from measurements by these standards laboratories make it

possible for all other laboratories to perform measurements on a common

basis

Material variability is determined by the degree of control exercised

during material production, and the sensitivity of property values to

physical and chemical variations in the material. As pointed out earlier,

however, transport properties at low temperatures are strongly dependent

on the detailed nature of the microscopic material structure. Because

of this, it is necessary to make measurements to determine the property

variability of a lot of material produced even under the best of conditions.

The only truly foolproof method of determining material variability effects

is to measure the property of interest on a random sampling of specimens

from the entire lot of material. For a thermal conductivity SRM, this

is costly and one must resort to less expensive characterization measurements and careful production record keeping to insure maximum benefit

from a minimum number of measurements.

23
4 5 10 50 100 500 1000

TEMPERATURE (K)

FIGURE 7 - Recommended Electrical Resistivity Values for

NBS Electrolytic Iron. (SRW 797).

24
Table 3. Electrical resistivity, SRM 797, Thermal

conductivity, SRM 734, and Lorenz ratio values for NBS electrolytic iron

Temp

(K) (Wm

1

K

1

)

P

(nfim) (V

2

K

2 xl0

8

)

6

78

9

10

38.8

45.3

51.8

58.2

64.7

3.87

3.87

3.85

3.85

3.85

2.50

2.50

2.49

2.49

2.49

12

14

16

18

20

77.4

89.7

101

113

123

3.87

3.89

3.90

3.90

3.92

2.50

2.49

2.47

2.43

2.42

25

30

35

40

45

50

55

60

65

70

146

162

171

173

171

167

160

153

145

139

3.99

4.10

4.26

4.50

4.84

5.28

5.85

6.54

7.37

8.32

2.33

2.21

2.08

1.95

1.84

1.76

1.70

1.67

1.65

1.65

75

80

85

90

95

100

132

127

122

117

114

110

9.38

10.56

11.88

13.27

14.76

16.32

1.66

1.67

1.70

1.73

1.77

1.80

110

120

130

140

150

105

101

98.3

95.8

93.8

19.69

23.30

27.07

31.0

35.0

1.88

1.97

2.05

2.12

2.19

160

170

180

190

200

92.0

90.3

88.9

87.5

86.2

39.1

43.2

47.5

51.8

56.1

2.25

2.30

2.34

2.38

2.42

25
Table 3. Electrical resistivity, SRM 797, Thermal conductivity,

SRM 734, and Lorenz ratio values for NBS electrolytic iron (continued)

Temp X P L

(K)

\ wm is. j \ui>SXl)

/'TT^Tr -2 , „8.

V.V K xiu ^

zzu (54.1) A ^ 9 DJ • Z

9 / Q z . 4y

Z'tu OZ8 9 T . j

7 A A / 4 . 4 Z

9 RR . J J

9zouah oU.O Q/i 9 o4 . Z9 A9 Z . OZ

ZoU 9«n 7 Q 1 Q/i "3 y4 . J Z

9 A7 . 0 / jUU 77 1

/ / . J. 9Z AS . DO

350 72.0 132 2.72

400 67.5 164 2.77

4 JU AT Q zuu 9nn Z9 . »Ao4

jUU DU. j Z4U 9An 9 8Q

JJU ^7 n Zo4 98 A Z9 . QAy4

600 53.7 333 2.98

650 50.2 387 2.99

/ uu A4 7 9 / . z. AA44 JS Ji nr> • uu /JU AA R JUO ouu A4 9Z 1

. X J^7/ AD Ji . n^Uj

850 39.5 649 3.01

900 37.2 728 3.00

950 34.8 811 2.97

1000 32.5 901 2.92

26

28
Fixed-point electrical resistivity, density, grain size, and hardness data have been compared earlier in the text. These comparisons

suggest that the effects of material variability in this electrolytic

iron are not larger than 1% in thermal conductivity and electrical

resistivity.

Although the SRM's described in this paper are considered quite

adequate for engineering use, improvement in the accuracy and credibility of the values presented would be improved with additional measurements. Through its use as an SRM this material will be measured

by other laboratories. These data will be compiled and when sufficient

reduction in uncertainty is achievable, the recommended values will be

updated. Anyone measuring this material with an absolute method is urged

to make the data available to the author.

8 . Summary

Recommended values of thermal conductivity (SRM 734) and electrical

resistivity (SRM 797) for NBS electrolytic iron at temperatures from

4 to 1000 K have been presented. The values up to 280 K are based on direct measurements by Hust and Sparks [17]. Above 280 K the values are based on measurements reported by Fulkerson et al [8] on a similar iron

and are confirmed by correlations with data for ingot iron. Material

variability of NBS electrolytic iron affects the above values by no more

than about ± 1%. Maximum uncertainties are estimated as follows:

Thermal Conductivity Electrical Resistivity

Below 280 K 2.5% 1%

Above 280 K 3 % 2%

These SRM's are available in the form of rods from the Office of

Standard Reference Materials, National Bureau of Standards, Washington,

D.C. 20234. Available sizes are as follows:

SRM 734-S (0.64 cm diameter, 30 cm long)

SRM 734-L1 (3.17 cm diameter, 15 cm long)

SRM 734-L2 (3.17 cm diameter, 30 cm long)

SRM 797-1 (0.64 cm diameter, 5 cm long)

SRM 797-2 (0.64 cm diameter, 10 cm long)

£RM 797-3 (0.64 cm diameter, 15 cm long)

Longer continuous lengths can be obtained by special order.

29
9 . Acknowledgements

This work has been in progress for several years and over this

period of time many people have assisted in various ways. R. L.

Powell was instrumental in suggesting the importance of the work and

in formulating the preliminary program. Larry L. Sparks assisted in the

measurement of thermal conductivity with the miltiproperty apparatus.

Last, but not least, we wish to thank R. E. Michaelis of NBS, OSRM

for supporting this work and for many helpful discussions.

30
10. References

1. M. J. Laubitz and D. L. McElroy, Precise Measurements of Thermal

Conductivity at High Temperatures (100 - 1200 K) , Metrologia 7_, No. 1, 1-15 (1971).

2. R. W. Powell, The Thermal and Electrical Conductivities of Metals

and Alloys: Part I, Iron from 0° to 800°C, Proc. Phys. Soc. 4_6,

659-679 (1934).

3. M. S. Van Dusen and S. M. Shelton, Apparatus for Measuring Thermal

Conductivity of Metals up to 600°C, Bur. Stand. J. Res. (USA) 12,

429-440 (1934).

4. C. F. Lucks, Armco Iron: New Concept and Broad-Data Base Justify

Its Use as a Thermal Conductivity Reference Material, J. of Testing

and Evaluation, 1, No. 5, 422-431 (1973).

5. J. G. Hust, Thermal Conductivity Standard Reference Materials from

4 to 300 K. I. Armco Iron, Proc. of the 9th Thermal Conductivity

Conference, Iowa State Univ., Ames, Oct. 6-8, 1969.

6. J. G. Hust, Robert L. Powell, and D. H. Weitzel, Thermal Conductivity

Standard Reference Materials from 4 to 300 K. I. Armco Iron:

Including Apparatus Description and Error Analysis, J. Res. Nat.

Bur. Stand. 74A, No. 5, 673-690 (1970).

7. J. G. Hust and L. L. Sparks, Thermal Conductivity of Electrolytic

Iron, SRM 734, from 4 to 300 K, Nat. Bur. Stand. Special Publication

260-31, 1971.

8. W. Fulkerson, J. P. Moore, and D. L. McElroy, Comparison of the

Thermal Conductivity, Electrical Resistivity, and Seebeck Coefficient

of a High-purity Iron and an Armco Iron to 1000° C, J. Appl. Phys.

37 No. 7, 2639-2653 (1966).

9. M. J. Laubitz and K. D. Cotnam, Thermal and Electrical Properties

of Inconel 702 at High Temperatures, Can. J. Phys. 4_2, 131-152 (1964).

10. H. E. Robinson and D. R. Flynn, The Current Status of Thermal

Conductivity Reference Standards at the National Bureau of Standards,

unpublished proceedings of the 3rd Thermal Conductivity Conference,

Oak Ridge National Laboratory, Oct. 16-18 (1963).

11. A. D. Little, Inc., Development of High Temperature Thermal Conductivity Standards, Technical Reports AFML-TR-66-415 (1967);

AFML-TR-69-2 (1969), Wright-Patterson Air Force Base, Ohio.

12. E. Fitzer, Thermophysical Properties of Solid Materials, Advisory

Report 12 (1967), Advisory Report 38 (1972); Report 606 (1972),

AGARD, NATO, France.

31
13. M. L. Minges, Evaluation of Selected Refractories as High Temperature Thermophysical Property Calibration Materials, AFML Technical

Report TR-73-278 (1974); Int'l. J. Heat and Mass Transfer, Pergamon

Press, London, (to be published in 1974)

14. J. G. Hust, Electrical Resistivity of Electrolytic Iron, SRM 797,

and Austenitic Stainless Steel, SRM 798, from 5 to 280 K, Nat. Bur.

Stand. Special Publication 260-47 (1974).

15. F. J. Blatt, Physics of Electronic Conduction in Solids, McGrawHill, New York (1968)

16. H. A. Bowman and R. M. Schoonover, Procedure for High Precision

Density Determinations by Hydrostatic Weighings, J. Res. Nat. Bur.

Stand. (U.S.) 71c, 179-198 (1967).

17. J. G. Hust and L. L. Sparks, Thermal Conductivity Standard Reference

Materials from 4 to 300 K: II OSRM Iron - 1265, unpublished

NBS Report (1970)

32
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. Special Publication 260-502. Gov 't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

STANDARD REFERENCE MATERIALS: Thermal Conductivity

and Electrical Resistivity Standard Reference Materials:

Electrolytic Iron, SRM's 734 and 797 from 4 to 1000 K

5. Publication Date June 1975

6. Performing Organization Code

7. AUTHOR(S)

J.t/-t_t*. G. Hust andjtit^- P. J. Giarratano 8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Same as #9 above.

13. Type of Report & Period Covered Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 74-619117

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

bibliography or literature survey, mention it here.) A historical review of the development of Standard Reference Materials, SRM's, is

given and selection criteria of SRM's are listed. Thermal conductivity and

electrical resistivity data for electrolytic iron and similar irons are compiled,

analyzed, and correlated. Recommended values of thermal conductivity and electrical

resistivity for electrolytic iron, SRM's 734 and 797, are presented for the range

4 to 1000 K. These values are based on NBS measurements up to 280 K and on measurements by Oak Ridge National Laboratory on a similar iron above 280 K. The

average uncertainty of the thermal conductivity values below ambient is 1.5% and

3% above ambient. The corresponding uncertainties in electrical resistivity are

1% and 2%.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons) Electrical resistivity; electrolytic iron; high temperature;

iron; Lorenz ratio; low temperature; Standard Reference Material; thermal

conductivity; thermopower.

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