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'V.\

v> NBS SPECIAL PUBLICATION 260-56

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

56
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

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NATIONAL BTJKEAT

Off STANDARDS

LIET5APY

-1 1978

Standard Reference Materials: /oo-h Qlcc .

STANDARD THERMOCOUPLE MATERIAL, Pt-67: SRM-1967 /oo

^ Special Pa\3\\(LOJt\0^ iqyi

Robert L. Powell, Larry L. Sparks

and J. G. Hust

Cryogenics Division

Institute for Basic Standards

National Bureau of Standards

Boulder, Colorado 80302

Sponsored by the

Office of Standard Reference Materials

National Bureau of Standards

Washington, D.C. 20234

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

U .^.NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

Issued February 1978
Library of Congress Cataloging in Publication Data

Powell, Robert L.

Standard thermocouple material, pt-67, SRM-1967.

(Standard Reference materials) (National Bureau of Standards

special publication ; 260-56)

Supt.ofDocs.no.: C13.10:260-56

1 . Thermocouples- -Standards. 2. Platinum- -Standards. I. Sparks,

Larry L., joint author. II. Hust, Jerome G., joint author. III. United

States. National Bureau of Standards. Office of Standard Reference

Materials. IV. Title. V. Series: United States. National Bureau of

Standards. Standard reference materials. VI. Series: United States. National Bureau of Standards. Special publication ; 260-56. QC100.U57 no. 260-56 [QC274] 602Ms [536\52] 77-29155

National Bureau of Standards Special Publication 260-56

Nat. Bur. Stand. (U.S.), Spec. Publ. 260-56, 50 pages (Feb. 1978)

CODEN: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1978

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

Stock No. 0O3-OO3-01886-4 Price $2.20

(Add 25 percent additional for other than U.S. mailing).
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

purpose

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 certificate so 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

Catalog of NBS Standard Reference Materials

(1975-76 edition), R. W. Seward, ed., NBS

Spec. Publ. 260 (June 1975). $1.50* SN003-003-

01445-1

Michaelis, R. E., and Wyman, L. L., Standard

Reference Materials: Preparation of White Cast

Iron Spectrochemical Standards, NBS Misc.

Publ. 260-1 (June 1964). COM74-1 1061**

Michaelis, R. E., Wyman, L. L., and Flitsch, R.,

Standard Reference Materials: Preparation of

NBS Copper-Base Spectrochemical Standards,

NBS Misc. Publ. 260-2 (October 1964). COM74-

11063**

Michaelis, R. E., Yakowitz, H., and Moore, G. A.,

Standard Reference Materials: Metallographic

Characterization of an NBS Spectrometric LowAlloy Steel Standard, NBS Misc. Publ. 260-3

(October 1964). COM74-1 1060**

Hague, J. L., Mears, T. W., and Michaelis, R. E.,

Standard Reference Materials: Sources of

Information, NBS Misc. Publ. 260-4 (February

> 1965). COM74-11059

Alvarez, R., and Flitsch, R., Standard Reference

Materials: Accuracy of Solution X-Ray Spectrometric Analysis of Copper-Base Alloys, NBS

Misc. Publ. 260-5 (March 1965). PB168068**

Shultz, J. I., Standard Reference Materials:

Methods for the Chemical Analysis of White

Cast Iron Standards, NBS Misc. Publ. 260-6

(July 1975). COM74-11068**

Bell, R. K., Standard Reference Materials:

Methods for the Chemical Analysis of NBS

Copper-Base Spectrochemical Standards, NBS

Misc. Publ. 260-7 (October 1965). COM74-

11067**

Richmond, M. S., Standard Reference Materials:

Analysis of Uranium Concentrates at the

National Bureau of Standards, NBS Misc. Publ.

260-8 (December 1965). COM74-1 1066**

Anspach, S. C, Cavallo, L. M., Garfinkel, S. B.,

Hutchinson, J. M. R., and Smith, C. N., Standard Reference Materials: Half Lives of Materials

Used in the Preparation of Standard Reference

Materials of Nineteen Radioactive Nuclides

Issued by the National Bureau of Standards,

NBS Misc. Publ. 260-9 (November 1965).

COM74-11065**

Yakowitz, H., Vieth, D. L., Heinrich, K. F. J., and

Michaelis, R. E., Standard Reference Materials:

Homogeneity Characterization on NBS Spectrometric Standards II: Cartridge Brass and LowAlloy Steel, NBS Misc. Publ. 260-10 (December

1965). COM74-11064**

Napolitano, A., and Hawkins, E. G., Standard

Reference Materials: Viscosity of Standard

Lead-Silica Glass, NBS Misc. Publ. 260-11

(November 1966). NBS Misc. Publ. 260-11**

Yakowitz, H., Vieth, D. L., and Michaelis, R. E.,

Standard Reference Materials: Homogeneity

Characterization of NBS Spectrometric Standards III: White Cast Iron and Stainless Steel

Powder Compact, NBS Misc. Publ. 260-12

(September 1966). NBS Misc. Publ. 260-12**

Spijkerman, J. I., Snediker, D. K., Ruegg, F. C,

and DeVoe, J. R., Standard Reference Materials: Mossbauer Spectroscopy Standard for the

Chemical Shift of Iron Compounds, NBS Misc.

Publ. 260-13 (July 1967). NBS Misc. Publ.

260-13**

Menis, O., and Sterling, J. T., Standard Reference

Materials: Determination of Oxygen in Ferrous

Materials - SRM 1090, 1091, and 1092, NBS

Misc. Publ. 260-14 (September 1966). NBS Misc.

Publ. 260-14**

Passaglia, E., and Shouse, P. J., Standard Refer- ence Materials: Recommended Method of Use

of Standard Light-Sensitive Paper for Calibrating Carbon Arcs Used in Testing Textiles for

Colorfastness to Light, NBS Misc. Publ. 260-15

(June 1967). (Replaced by NBS Spec. Publ.

260-41.)

Yakowitz, H., Michaelis, R. E., and Vieth, D. L.,

Standard Reference Materials: Homogeneity

Characterization of NBS Spectrometric Standards IV: Preparation and Microprobe Characterization of W-20% MO Alloy Fabricated by

Powder Metallurgical Methods, NBS Spec.

Publ. 260-16 (January 1969). COM74-1 1062**

Catanzaro, E. J., Champion, C. E., Garner, E. L.,

Marinenko, G., Sappenfield, K. M., and Shields,

W. R., Standard Reference Materials: Boric

Acid; Isotopic and Assay Standard Reference

Materials, NBS Spec. Publ. 260-17 (February

1970). Out of Print

iv
Geller, S. B., Mantek, P. A., and Cleveland, N.

G., Standard Reference Materials: Calibration of NBS Secondary Standard Magnetic Tape

(Computer Amplitude Reference) Using the

Reference Tape Amplitude Measurement

"Process A," NBS Spec. Publ. 260-18 (November

1969). (See NBS Spec. Publ. 260-29.)

Paule, R. C, and Mandel, J., Standard Reference

Materials: Analysis of Interlaboratory Measurements on the Vapor Pressure of Gold (Certification of Standard Reference Material 745), NBS

Spec. Publ. 260-19 (January 1970). PB190071**

Paule, R. C, and Mandel, J., Standard Reference

Materials: Analysis of Interlaboratory Measurements on the Vapor Pressures of Cadmium and

Silver, NBS Spec. Publ. 260-21 (January 1971).

COM74-11359**

Yakowitz, H., Fiori, C. E., and Michaelis, R. E.,

Standard Reference Materials: Homogeneity

Characterization of Fe-3 Si Alloy, NBS Spec.

Publ. 260-22 (February 1971). COM74-1 1357**

Napolitano, A., and Hawkins, E. G., Standard

Reference Materials: Viscosity of a Standard

Borosilicate Glass, NBS Spec. Publ. 260-23

(December 1970). COM71-00157**

Sappenfield, K. M., Marineko, G., and Hague, J.

L., Standard Reference Materials: Comparison

of Redox Standards, NBS Spec. Publ. 260-24

(January 1972). COM 72-50058**

Hicho, G. E., Yakowitz, H., Rasberry, S. D., and

Michaelis, R. E., Standard Reference Materials:

A Standard Reference Material Containing

Nominally Four Percent Austenite, NBS Spec.

Publ. 260-25 (February 1971). COM 74-1 1356**

Martin, J. F., Standard Reference Materials:

National Bureau of Standards-US Steel Corportion Joint Program for Determining Oxygen and

Nitrogen in Steel, NBS Spec. Publ. 260-26

(February 1971). 85 cents* SN003-003-00786-2

Garner, E. L., Machlan, L. A., and Shields, W. R.,

Standard Reference Materials: Uranium

Isotopic Standard Reference Materials, NBS

Spec. Publ. 260-27 (April 1971). COM74-

11358**

Heinrich, K. F. J., Myklebust, R. L., Rasberry, S. D., and Michaelis, R. E., Standard Reference

Materials: Preparation and Evaluation of

SRM's 481 and 482 Gold-Silver and GoldCopper Alloys for Microanalysis, NBS Spec.

Publ. 260-28 (August 1971). COM7 1-50365**

Geller, S. B., Standard Reference Materials: Calibration of NBS Secondary Standard Magnetic

Tape (Computer Amplitude Reference) Using

the Reference Tape Amplitude Measurement

"Process A-Model 2," NBS Spec. Publ. 260-29

(June 1971). COM71-50282**

Gorozhanina, R. S., Freedman, A. Y., and

Shaievitch, A. B. (translated by M. C. Selby),

Standard Reference Materials: Standard

Samples Issued in the USSR (A Translation

from the Russian), NBS Spec. Publ. 260-30 (June

1971). COM71-50283**

Hust, J. G., and Sparks, L. L., Standard Reference

Materials: Thermal Conductivity of Electrolytic

Iron SRM 734 from 4 to 300 K, NBS Spec. Publ.

260-31 (November 1971). COM71-50563**

Mavrodineanu, R., and Lazar, J. W., Standard

Reference Materials: Standard Quartz Cuvettes,

for High Accuracy Spectrophotometry, NBS

Spec. Publ. 260-32 (December 1973). 55 cents*

SN003-003-01213-1

Wagner, H. L., Standard Reference Materials:

Comparison of Original and Supplemental

SRM 705, Narrow Molecular Weight Distribution Polystyrene, NBS Spec. Publ. 260-33

(May 1972). COM72-50526**

Sparks, L. L., and Hust, J. G., Standard Reference

Materials: Thermoelectric Voltage, NBS Spec.

Publ. 260-34, (April 1972). COM72-50371**

Sparks, L. L., and Hust, J. G., Standard Reference Materials: Thermal Conductivity of

Austenitic Stainless Steel, SRM 735 from 5

to 280 K, NBS Spec. Publ. 260-35 (April 1972.)

35 cents* COM72-50368**

Cali, J. P., Mandel, J., Moore, L. J., and Young, D.

S., Standard Reference Materials: A Referee

Method for the Determination of Calcium in

Serum, NBS SRM 915, NBS Spec. Publ. 260-36

(May 1972). COM72-50527**

Shultz, J. I., Bell, R. K., Rains, T. C, and Menis,

O., Standard Reference Materials: Methods of

Analysis of NBS Clay Standards, NBS Spec.

Publ. 260-37 (June 1972). COM72-50692**

Richmond, J. C, and Hsia, J. J., Standard Refer- ence Materials: Preparation and Calibration of

Standards of Spectral Specular Reflectance,

NBS Spec. Publ. 260-38 (May 1972). COM72-

50528**

Clark, A. F., Denson, V. A., Hust, J. G., and

Powell, R. L., Standard Reference Materials:

The Eddy Current Decay Method for Resistivity

Characterization of High-Purity Metals, NBS

Spec. Publ. 260-39 (May 1972). COM72-50529**

McAdie, H. G., Garn, P. D., and Menis, O., Standard Reference Materials: Selection of Thermal

Analysis Temperature Standards Through a

v
Cooperative Study (SRM 758, 759, 760), NBS

Spec. Publ. 260-40 (August 1972.) COM-72

50776**

Wood, L. A., and Shouse, P. J., Standard

Reference Materials: Use of Standard LightSensitive Paper for Calibrating Carbon Arcs

Used in Testing Textiles for Colorfastness to

Light, NBS Spec. Publ. 260-41 (August 1972)

COM72-50775**

Wagner, H. L., and Verdier, P. H., eds., Standard

Reference Materials: The Characterization of

Linear Polyethylene, SRM 1475, NBS Spec.

Publ. 260-42 (September 1972). COM72-

50944**

Yakowitz, H., Ruff, A. W., and Michaelis, R. E.,

Standard Reference Materials: Preparation and

Homogeneity Characterization of an Austenitic

Iron-Chromium-Nickel Alloy, NBS Spec. Publ.

260-43 (November 1972). COM73-50760**

Schooley, J. F., Soulen, R. J., Jr., and Evans, G. A.,

Jr., Standard Reference Materials: Preparation

and Use of Superconductive Fixed Point

Devices, SRM 767, NBS Spec. Publ. 260-44

(December 1972). COM73-50037**

Greifer, B., Maienthal, E. J., Rains, T. C, and

Rasberry, S. D., Standard Reference Materials:

Powdered Lead-Based Paint, SRM 1579, NBS

Spec. Publ. 260-45 (March 1973). COM73-

50226**

Hust, J. G., and Giarratano, P. J., Standard Refer- ence Materials: Thermal Conductivity and

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

798, from 4 to 1200 K, NBS Spec. Publ. 260-46

(March 1975). SN003-003-0 1278-5

Hust, J. G., Standard Reference Materials: Electrical Resistivity of Electrolytic Iron, SRM 797,

and Austenitic Stainless Steel, SRM 798, from 5

to 280 K, NBS Spec. Publ. 260-47 (February

1974). COM74-50176**

Mangum, B. W., and Wise, J. A., Standard Refer- ence Materials: Description and Use of Precision

Thermometers for the Clinical Laboratory,

SRM 933 and SRM 934, NBS Spec. Publ. 260-48

(May 1974). 60 cents* SN003-003-0 1278-5

Carpenter, B. S., and Reimer, G. M., Standard

Reference Materials: Calibrated Glass Standards for Fission Track Use, NBS Spec. Publ.

260-49 (November 1974). SN003-O03-0 1344-7

Hust, J. G., and Giarratano, P. J., Standard Refer- ence Materials: Thermal Conductivity and Electrical Resistivity Standard Reference Materials:

vi

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

1000 K, NBS Spec. Publ. 260-50 (June 1975).

1.00* SN003-0O3-0 1425-7

Mavrodineanu, R., and Baldwin, J. R., Standard

Reference Materials: Glass Filters As a Standard

Reference Material for Spectrophotometry;

Selection; Preparation; Certification; Use -SRM

930, NBS Spec. Publ. 260-51 (November 1975).

$1.90* SN003-003-01481-8

Hust, J. G., and Giarratano, P. J., Standard Refer- ence Materials: Thermal Conductivity and Electrical Resistivity Standard Reference Materials

730 and 799, from 4 to 3000 K, NBS Spec. Publ.

260-52 (September 1975). $1.05* SN003-O03-

01464-8

Durst, R. A., Standard Reference Materials:

Standardization of pH Measurements, NBS

Spec. Publ. 260-53 (December 1975, Revised).

$1.05* SN003-003-01551-2

Burke, R. W., and Mavrodineanu, R., Standard

Reference Materials: Certification and Use of

Acidic Potassium Dichromate Solutions as an

Ultraviolet Absorbance Standard, NBS Spec.

Publ. 260-54 (August 1977). $3.00* SN003-O03-

01828-7

Ditmars, D. A., Cezairliyan, A., Ishihara, S., and

Douglas, T. B., Standard Reference Materials:

Enthalpy and Heat Capacity; Molybdenum

SRM 781, From 273 to 2800 K, NBS Spec. Publ.

260-55 (September 1977). $2.20* SN003-003-

01836-8

Powell, R. L., Sparks, L. L., and Hust, J. G.,

Standard Reference Materials: Standard

Thermocouple Material, Pt.-67:SRM1967, NBS

Spec. Publ. 260-56 (in press).

Cali, J. P. and Plebanski, T., Guide to United

States Reference Materials, NBS Spec. Publ.

260-57 (in press). * Send order with remittance to: Superintendent

of Documents, US Government Printing

Office, Washington, DC 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.
Contents

Page

1. Introduction 1

2. Historical Development 5

3. Material Characterizations 7

4. Low- Temperature Thermoelectric Measurements 11

5. High- Temperature Thermoelectric Measurements 23

6. Effects of Imperfections 27

7. Recommendations for Usage 31

8. Acknowledgments 36

9. References 37

List of Tables

Table Page

1. Defining fixed points of the IPTS-68 3

2. Secondary reference points of the IPTS-68 4

3. Chemical composition of Pt-67 . . 8

4. Thermoelectric voltage for Pt-67 versus commonly

used thermocouple wire between liquid nitrogen

(76K) and ice (273. 15K) fixed points 19

5. Effects of impurities on electrical properties

of platinum 33

vii
List of Figures

1. Residual resistance ratio for five specimens

from Pt-67 10

2. Four object measurement graph. 13

3a. Details of thermocouple comparator (pictorial view). ... 17

3b. Details of thermocouple comparator (wiring diagram). ... 18

4a. Typical thermocouple arrangement 20

4b. Comparator circuit for calibration of standard

reference thermocouple wires 20

5. Intercomparisons of three Pt-67 comparators between 76

and 273.15 K via a common thermocouple wire. The error

bars are ± 2(7 values 21

6. Thermoelectric comparisons of Pt-67 between 76 and

273.15 K at equally spaced points along the entire

length in stock 24

7. High temperature calibration system for platinum

thermoelements 26

8. Thermoelectric voltage for Type S thermocouples. The

circles indicate values at various thermoelectric reference temperatures on the IPTS-68 28

9. Seebeck coefficient for Type S thermocouples. The circles

indicate values at various thermoelectric reference

temperatures on the IPTS-68 29

10. Second derivative of thermoelectric voltage for Type S

thermocouples. The circles indicate values at various

thermoelectric reference temperatures on the IPTS-68 ... 30

11. Deviation of thermoelectric voltage for two platinum

thermoelements at low temperatures 32

12. The specific effect of impurities on the high i temperature

thermoelectric voltage of platinum , 34

viii
Standard Reference Materials:

STANDARD THERMOCOUPLE MATERIAL, Pt-67: SRM-I967

Robert L. Powell, Larry L. Sparks, and J. G. Hust

Cryogenics Division

Institute for Basic Standards

National Bureau of Standards

Boulder, Colorado 80302

Industry-wide standardization of thermocouple wire depends in part on

thermoelectric comparisons of commercial wires to a standard. In this

paper we describe a thermoelectric standard, designated Pt-67, which is

available in wire form as a Standard Reference Material (SRM 1967).

High purity platinum meets the requirements of a thermoelectric reference

material for temperatures from 77K (-197 °C) up to 2040K (1767 °C) . Thermoelectric voltages, residual resistance ratios, temperature coefficients of resistance, and chemical composition are reported for a high

purity, highly characterized lot of platinum that has been developed as

a thermoelectric standard, Pt-67. A review of the historical development of the material is followed by characterization data on the material and descriptions of the cryogenic and high temperature apparatus.

The important effects of impurities are also described. Recommendations

and precautions for usage of the reference material conclude the discussion.

Keywords: Chemical composition; effects of imperfections; high

purity platinum; high temperature thermoelectric measurements; low

temperature thermoelectric measurements; platinum; Pt 67; residual

resistivity ratio; Standard Reference Material; temperature coefficient

of resistors; thermocouple; thermoelectric standard; thermoelectric

voltage.

1 . INTRODUCTION

The ability to standardize thermocouple wires depends in part on

the availability of a reliable Standard Reference Material (SRM) . In addition, commercial thermocouple materials must be well characterized

if excessive manufacturer-to-manufacturer, batch-to-batch, or spool-tospool variations are to be avoided. Because of the difficulty of accurately characterizing thermocouple wires (especially base-metal alloys)

in terms of composition, they must be controlled primarily by direct

thermoelectric measurements. If these direct thermoelectric measurements

are made with respect to a SRM which, in turn, is compared to standard

reference data, then industry-wide uniformity is possible. The first

step of this program, to experimentally establish such standard reference data, has been completed at cryogenic temperatures by Sparks et

al. [1] and at high temperatures by Powell, et al. [2]. The next step,

the establishment of a SRM, is described in this Special Publication.

1
The electrical characteristics of high purity platinum have been

well established primarily because of platinum's extensive use in interpolating thermometers for measuring temperatures on the international

temperature scales of ITS-27 , IPTS-48, and IPTS-68. The platinum resistance

thermometer is used from 13.81K (-259.34 °C) to 630.74 °C and the Pt-10%

Rh vs Pt thermocouple is specified for higher temperatures from 630.74 to

1064.43 °C. Platinum is used by thermocouple wire manufacturers for

production control of commercial thermocouples and by standards laboratories for calibrations because of its fundamental standing in the

temperature scales and because it is relatively easy to obtain as

reproducible, high-purity, well-characterized material.

Pure platinum and three alloys of platinum with rhodium are commonly

used for high temperature thermocouple thermometry. The three standardized

combinations are: (1) Platinum - 10% rhodium versus platinum (Type S)

,

(2) platinum - 13% rhodium versus platinum (Type R) , and (3) platinum - 30% rhodium versus platinum - 6% rhodium (Type B) . (It is conventional

in thermocouple thermometry to name the positive thermoelement first in

specifying thermocouple combinations.) Usually only pure platinum and

the Type S combination are used as reference materials for thermocouple

calibrations at temperatures above 0 °C.

The platinum - 10% rhodium thermocouple was developed and tested by

Le Chatelier almost a century ago. Because of his pioneer work, this

type of thermocouple was often referred to as the Le Chatelier couple.

In this country the ASTM E-20 and ISA-C96 standards for this thermocouple

type were formerly taken from NBS Circular 561 by Shenker et al. [3].

The reference tables given in NBS Circular 561 were based on functions

given by Roeser and Wensel [4] in 1933, as revised to conform with IPTS48. In Great Britain the British Standards Institution Table BS 1826

for this thermocouple type was based on the research by Barber [5] in

1950. There were considerable differences between the American and

British reference tables because of small differences in rhodium content,

in amount of iron impurities, in purity of platinum, and in realizations

of the temperature scales.

For many industrial applications, other noble metal thermocouples,

Types R and B described above, have preferable characteristics and have

replaced the Type S platinum - 10% rhodium vs platinum thermocouple.

However, Type S thermocouples remain the standard for determining

temperatures between 630.74 °C and the freezing point of gold (1064.43

°C). The official CIPM article (as amended in 1975) [6] details the

temperature scale definition in this range and includes specifications

on the limits of the thermocouple voltage. The other fixed point used

for determining the constants in the specified quadratic interpolation

formula of the thermoelectric voltage is the freezing point of silver,

961.93 °C. The primary and secondary fixed points of the IPTS-68 in the

temperature range suitable for platinum reference thermoelements are

given in tables 1 and 2, respectively. Modern methods of realizing

those fixed points were reviewed during the Fifth Symposium on Temperature in 1971 [7]

.

2
Table 1 Defining fixed points of the IPTS-68'

Equilibrium state

quilibrium between the liquid and vapor phases of oxygen (boiling point of oxygen)

quilibrium between the solid, liquid and vapor phases of water (triple point of water)'

quilibrium between the liquid and vapor phases of water (boiling point of water) b ' c

quilibrium between the solid and liquid phases of zinc (freezing point of zinc)

quilibrium between the solid and liquid phases of silver (freezing point of silver)

quilibrium between the solid and liquid phases of gold (freezing point of gold)

Assigned value of International

Practical Temperature

T«s (K) '68 (°C)

90.188 -182.962

273.16 0.01

373.15 100

692 . 73 419.58

1235.08 961.93

1337.58 1064.43

aEntries ire limited to those suitable for use with platinum reference thermoelements. The assigned values of temperature are

for equilibrium states at a pressure pQ ;i standard atmosphere ( 101 325 N/m^). 1" the realization of the fixed" points small

departures from the assigned temperatures will occur as a result of the differing immersion depths of thermometers or the failure

to realize the required pressure exactly. If due allowance is made for these small temperature differences, thev will not affect the accuracy of realization of the Scale. The magnitudes of these differences are given in section JII of the original article by

CIPM (6).

b The equilibrium state between the solid and liquid phases of tin (freezing point of tin) nas the assigned value of f 68 = 231.9681 C

id may be used as an alternative to the boiling point of water.

c The water used should have the isotopic composition of ocean water, see section 111, 4, ot the orginal article by Ll^M (6).

3
Table 2. Secondary reference points of the IPTS—68

Equilibrium state

International Practical Temperature

Tn (K) '68 (° Q

Equilibrium between the liquid and vapor phases of nitrogen (boiling point of nitrogen)

p B Ttg

lg— = A+—+C lg— +DTM +ET^

po Ta C= -2.3668, D-

(25)

,4=5.893 271, fl= -403 . 960 46K , £

, =72.5872X10-«K-2

, T

q

= 77.344

for the temperature range from 63. 146 K to 84K.

Equilibrium between the liquid and vapor phases of oxygen

p B T6S lg- = A+—+C \ g—+DT„+ETtt po Teg .4=5.961 546, B= —467.455 76 K,

-0.014 281 5K

£

, =50.8041X10~6 K

-2

> T

Q

= 90.188K

To C= -1.664 512,

(26)

D= -0.013 213 01 K

_1

,

for the temperature range from 54.361 K to 94 K.

Equilibrium between the solid and vapor phases of carbon dioxide (sublimation point of carbon

dioxide)

j = ^194 . 674 +12 . 264^-—1^ - 9 . 15^- -

1^

K (27)

for the temperature range from 194 K to 195 K.

Equilibrium between the solid and liquid phases of mercury (freezing point of mercury) b

Equilibrium between ice and air-saturated water (ice point)

Equilibrium between the solid, liquid and vapor phases of phenoxybenzene (diphenyl ether) (triple

point of phenoxybenzene)

Equilibrium between the solid, liquid and vapor phases of benzoic acid (triple point of benzoic acid)

Equilibrium between the solid and liquid phases of indium (freezing point of indium) b

Equilibrium between the solid and liquid phases of bismuth (freezing point of bismuth) b

Equilibrium between the solid and liquid phases of cadmium (freezing point of cadmium) b

Equilibrium between the solid and liquid phases of lead (freezing point of lead) b

Equilibrium between the liquid and vapor phases of mercury (boiling point of mercury)

*68 = ^356.66+55.552^— -1^-23.03^— -1^ +14.0^--!^ ° (28)

for p = 90 X 10 3 N/m2 to 104 X 10 3 N/ms

.

Equilibrium between the liquid and vapor phases of sulphur (boiling point of sulphur)

*68 = |^444 . 674 +69 . 010^— -

1^ - 27 . 48^— —

1^ +19. 14^— -

1^

(29)

for/> = 90Xl03 N/m2 to 104X103 N/m2

. Equilibrium between the solid and liquid phases of the copper-aluminum eutectic

Equilibrium between the solid and liquid phases of antimony (freezing point of antimony) b

Equilibrium between the solid and liquid phases of aluminum (freezing point of aluminum)

Equilibrium between the solid and liquid phases of copper (freezing point of copper)

Equilibrium between the solid and liquid phases of nickel (freezing point of nickel)

Equilibrium between the solid and liquid phases of cobalt (freezing point of cobalt)

Equilibrium between the solid and liquid phases of palladium (freezing point of palladium)

77.344 -195.806

194.674 -78.476

234. 314 -38 .8 36

273. 15 0

300.02 26.87

395 . 52 122.37

429.784 156.634

544.592 271.442

594.258 321.108

600.652 327 . 502

629.81 356.66

717.824 444.674

821.41 548. 26

903 . 905 630. 7 55

933. 61 660.46

1358.03 1084.88

1728 1455

176 8 1495

1827 1554

aEntries are limited to those suitable for use with platinum reference thermoelements. The assigned values of temperature are

for equilibrium states at a pressure pQ = i standard atmosphere ( 10 1 325 N/m2)- In the realization of the fixed points small

departures from the assigned temperatures will occur as a result of the differing immersion depths of thermometers or the failure

to realize the required pressure exactly. If due allowance is made for these small temperature differences, they will not affect the accuracy of -ealization of the Scale. The magnitudes of these differences are given in section III of the original article by

CIPM ffiV bSee the original article by CIPM (6) for the effect of pressure variations on these freezing points.
Because of the differences between the British and American standards

for Type S thermocouples noted above, an international program was begun

several years ago to rectify the unsatisfactory disagreements and to establish a common set of standard reference tables. Unfortunately the

highest purity platinum was not used as the common negative reference

material for that program, so a small correction must be applied to

values for Type S thermocouples to reference them to the Pt-67 wire

described in this Special Publication. However, the correction is

automatically accounted for whenever any positive or negative thermoelement is calibrated directly, or indirectly, against the standard

platinum described in this Special Publication. The program involved

cooperation of three national laboratories—the National Bureau of

Standards (USA) , the National Physical Laboratory (UK) , and the National

Research Council (Canada) —and seven manufacturers in Great Britain and

the United States. The thoroughly documented experimental details have

been published by Bedford et al. [8] and tables and functions have also

been published by Powell et al. [2].

Pt-67 (or SRM 1967) is the designation for the new platinum thermoelectric reference standard mat erial that is maintained by the Office of

Standard Reference Materials. It replaces the former standard, Pt-27,

which was used from 1922 up until January, 1973. A history of Pt-27 was

given by Wickers [9]. Pt-67 is a selected, highly-homogeneous, portion

of the chemical composition standard, SRM 680, that was set aside to be

developed as the thermoelectric standard. The historical development of

Pt-67 will be described in the next section. It should be noted that

Pt-27 stands for a batch number and Pt-67 stands for a date of preparation. Characterization of this reference material is described in

section 3. The low temperature and high temperature thermoelectric

measurements are briefly discussed in sections 4 and 5. The important

effects of impurities are given in section 6. The last section, 7,

includes recommendations for proper usage of this reference material,

Pt-67.

At temperatures below about 50K, the thermoelectric power of

platinum becomes strongly dependent on trace impurities. Thus platinum

is not recommended for standard reference thermoelectric measurements

below liquid nitrogen temperatures (77K) . An Ag-Au alloy, SRM 733, has

been established for use to 4K [l6] . The present paper describes

the work which has been done to certify and characterize high purity

platinum for use as a thermocouple reference material between 77K and

2040K (1767 °C).

2. HISTORICAL DEVELOPMENT

The predecessor of Pt-67 was Pt-27. The early development of the

latter was described by Wickers [9]. Early in 1922 a trial melt of

platinum, numbered as 27, was found to be thermoelectrically negative to

all previous specimens, and therefore by inference, to be more pure.

(Note that Pt-27 refers to a batch number, but Pt-67 refers to a date.)

Unfortunately, that trial melt only provided about 1 meter of wire for

thermoelectric calibrations. Over the years, it was consumed and other

5
batches of wire were used, though the reference values were still referred

to Pt-27. Gradually the apparent value of thermoelectric voltage drifted

until it was arbitrarily, by decree, revised back toward a value more

representative of highest purity material. A precise history of the

original material and its successors is difficult to trace, but in 1949

R. J. Corruccini reviewed the status of Pt-27 and recorded his comments

in a laboratory notebook [ll] . The situation was obviously undesirable

for a national standard, and new research on the preparation and

characterization of high purity platinum was begun some 10 years later.

Representatives of major platinum refiners were aware of the need

for reference material that was more pure and better characterized than

the earlier Pt-27. In fact, improved industrial and chemical methods

allowed the preparation and widespread usage of considerably better

platinum wire. On December 14, 1959, representatives of J. Bishop &

Co., Sigmund Cohn Corp.; Johnson, Matthey Co., Inc; and Engelhard

Industries, Inc. met in the offices of Johnson Matthey & Co. in New

York, to plan a joint cooperative test program on high purity platinum

[12]. A follow-up meeting was held on August 19, 1960, at Engelhard

Ind. , Inc. in New Jersey. Soon thereafter members of the National

Bureau of Standards actively entered the program. On September 1, 1960,

a conference was held at the Van Ness Street campus of the National

Bureau of Standards in Washington, D.C. That meeting was attended by

NBS and industry representatives, Mr. J. F. Swindells of NBS presiding.

Other NBS staff included F. R. Caldwell, J. P. Evans, R. Gilchrist, W. F.

Roeser, B. F. Scribner, and E. Wickers. H. J. Albert, H. C. Anderson,

Arnold J. Lincoln, and E. Zysk represented Engelhard Ind.; John Cochrane

represented Johnson, Matthey & Co.; and B. Brenner represented Sigmund Cohn

Corp. At that meeting it was agreed that the manufacturers would prepare a high purity lot of material and would characterize it as well as they could.

Other chemical and physical characterization tests, in particular the high

temperature thermoelectric measurements, would be simultaneously carried out

at the National Bureau of Standards. Later R. E. Honig of the RCA Laboratories joined the program to provide mass spectroscopic analyses.

After considerable effort by many individuals and organizations,

the material was finally prepared and characterized and then certified

as a Standard Reference Material (SRM 680) on December 28, 1967. The

material for SRM 680 was prepared at Sigmund Cohn by induction melting

of high purity platinum sponge in a zirconium silicate crucible, and by

casting into a platinum-lined, water-cooled copper mold. The ingot was

trimmed, swaged, and drawn into wire using the utmost precautions to

minimize contamination. The best specimens, based on resistivity measurements, from that lot were selected as thermoelectric standards and

were distributed to several national standardizing laboratories. R. E.

Michaelis of the OSRM suggested that because of the certification date,

the platinum should become known as Pt-67 . A select portion of the

chemical standard, SRM 680, has now become certified as a thermophysical

standard SRM 1967.

6
Cooperating with the National Bureau of Standards in this extensive

analytical program were the following American and British manufacturers

and laboratories: Matthey Bishop, Inc.; Sigmund Cohn Corp.; Engelhard

Industries, Inc.; Johnson, Matthey Co., Ltd.; and RCA Laboratories.

3. MATERIAL CHARACTERIZATIONS

A high-purity lot of platinum, designated SRM 680 has received

extensive characterization under the direction of the Office of Standard

Reference Materials (OSRM) , National Bureau of Standards. The material

for Pt-67 was selected from SRM 680 platinum. SRM 680 platinum was

prepared as described in the previous section.

This lot of platinum wire, SRM 680, was found satisfactory with respect

to homogeneity and was subsequently certified for chemical composition.

The chemical composition of Pt-67, SRM 1967, is given in table 3 where the

data are the recommended values taken from the previous chemical certificate of analysis for SRM 680. The elemental analyses were made by the

following analytical methods: optical emission spectrography , spark source

mass spectrography (with isotopic dilution), polarography , spectrophotometry, activation analysis, and vacuum fusion.

The temperature coefficient of electrical resistance between 0 and

100 °C is commonly used as an indicator of the quality of platinum used

in thermometry. The alpha coefficient is defined by:

R (100 °C) - R (0 °C)

01 = R (0 °C)

_o

The IPTS-68 [6] requires an alpha coefficient of 3.925 x 10 /°C or

higher for platinum used as an interpolating thermometer. Two specimens

from the lot of Pt-67 wire were tested by each of four cooperating

laboratories (National Bureau of Standards, Engelhard, Johnson Matthey,

and Sigmund Cohn) and the values reported for the temperature coefficient

of resistance, a, ranged from 3.926 to 3.9275 x 10~3k~1. The average value

for ten determinations was 3.9269 (°±0.001i) x 10~3K

-1 where the indicated

uncertainty is the 2 a value.

Each of the four cooperating laboratories listed above also determined the thermoelectric voltage of two specimens of Pt-67 against

representative specimens that were descendants of the former standard,

Pt-27. For measuring junction temperatures of 1200 °C and reference

junctions at 0 °C, values of -9 and -10 microvolts were reported. (Note

that many current comparisons are made at 1100 °C . ) As could be expected

from its greater purity and lack of iron and rhodium impurities, Pt-67 is

thermoelectrically negative with respect to Pt-27. The value determined by

the National Bureau of Standards, -9 microvolts, is used as a standard

correction. For a reference junction at 0 °C, thermoelectric voltage

versus temperature relationship of Pt-67 with respect to Pt-27 can be

approximated by:

7
Table 3. Chemical Composition of Pt-67, SRM 1967

Element Recommended Range of

Value Values Reported

3 Concentration in Parts Per Million by Weight

Copper 0. 1 0. 087 - <1

Silver <0. 1 ( < 0. 06 - <1

Palladium 0. 2 ( < 0. 1 - <1

Lead <1 ( 0. 6 - 3

Iron 0. 7 ( 0. 6 - 2.6

Nickel <1 0. - <1

Gold <1 ( < 0. 1 - 8

Magnesium <1 ( < 0. 05 - 2

Zirconium <0. 1 ( < 0. 03 - 0.3

Rhodium <0. 2 0. 09 - <1

Iridium <0. 01 0. 007 - 0.01

Oxygen 4 3. 2 - 5.2

Platinum (remainder - 99.999 +%)

Range from one laboratory only.

1. This is the same chemical composition that was certified for SRM 680,

High-Purity Platinum, December 28, 1967.

2. Other elements are also contained in the standards; some of them such

as Al, Ca, Na, Si, and Sn may be certified at a later date.

3. The values listed are based on a consideration of the analytical

methods and results reported by cooperating laboratories. For all

elements in SRM 1967, either because a single method was used or

because of lack of agreement among methods, no estimate of accuracy

can be made at this time.

8
^67-27

=

"7 - 5 X 10

"3t

68

where AE is expressed in microvolts and t68 i- n degrees Celsius (1968)

.

This relation was found to be valid over the range -197 to +1200 °C to

within the estimated limits of experimental uncertainty (about ±1 uV

below 600 °C, increasing to about ±2 yV at 1200 °C). There was insufficient data available to substantiate the validity of the relation

outside this temperature range. However, data available from other

high-purity platinum wires support its extrapolation to higher temperatures, but not to lower temperatures. At very low temperatures most

high purity metal wires become unduly sensitive thermoelectrically to

minute amounts of trace impurities. The quantitative results given

above were obtained with specimens of Pt-67 wire which had been electrically annealed in air for 10 minutes at 1200 °C and slowly cooled to

room temperature.

The various methods for characterizing thermocouples at high temperatures have been described in considerable detail by Roeser and Lonberger

113] . The two main high- temperature methods of characterization, thermoelectric voltage and temperature coefficient of resistance, have moderate

sensitivity. A more sensitive measure of both the effective electrical

purity and the state of physical perfection is the residual resistance

ratio,

RRR _ R (273 K) RRR " R (0 K)

The residual resistance R (0 K) is well approximated for most metals by

the resistance at liquid helium temperatures, about 4.2 K. For most

metal specimens, there is no further decrease of resistance below 4.2 K.

Bulk specimens may be characterized by the eddy current decay method

which has been described in a previous OSRM publication by Clark et al.

[14] . Thin wires may be characterized by the more simple four-probe

electrical resistance method. Values of RRR were determined from

liquid helium and ice point resistance measurements for five specimens

taken at equally separated points along the lot of Pt-67 wire. The

measured values are shown in figure 1. The average ratio for these

five measurements is 3496. Specimen preparation prior to these tests

consisted of cleaning in aqua regia for 12 minutes at 50 °C, rinsing in

distilled water, annealing in air at 600 °C for 1 hour, and slow cooling

to room temperature. It should be noted that this method is sufficiently

precise to show inhomogeneity variations not clearly observed utilizing

other methods.

The principal measurements made to characterize this wire as a

cryogenic thermoelectric standard were performed in cryogenic comparators

specifically designed to minimize handling and temperature cycling

damage to the standard and test wires. A description of these comparators

and their use is given in the next section.

9
T3C

Ld~ ^ CM "O \ \ 0 — — ro

tt)

-oc

LlIo>c

5f

=o

— OO r-i cm ro st in c c c c c

CD CD <L> <D <D E E E E E o o o o o

CD CD (1) CD <l) q a a Q a

CO CO CO CO CO

oo

+1

II

"a>

<r> c

a>oc

a) •ocoo

lO

CD 8

ro

OO

CDro

OO

in

ro

oo

to

m

CD

— ro UJO

LlI <M CL

cn 8ro

to

vOI 4-1 P-ieon

IH

coC

(UE

•HO

aja

CD

0)>oo

•H

4-1

>-)

CDac

cc

4-J CO •H

CO

cu

J-l

X)

•H

CO

CU Pi

Ml •H

10
The melting point of high-purity platinum is used as one of the

secondary fixed points in the IPTS-68. Its assumed temperature is 1772

°C. However, Quinn and Chandler [15] of the National Physical Laboratory

in Teddington, England, have more recently carried out extremely well

controlled experiments on the melting point of platinum and have determined a value of 1767.6 ±0.3 °C. Their paper includes a detailed

discussion of the effects of possible impurities and systematic experimental errors. Similar discrepancies and variations in realizing thermodynamic temperatures from determinations of the IPTS-68 temperatures can

be significant for accurate thermophysical measurements. Those variations and the resultant precautions that are necessary are described

more fully in section 5.

For accurate thermometry, one must insure that the temperature

sensor truly measures the desired unknown temperature and is not affected

significantly by the external environment. Some of the necessary experimental precautions have been described by Hust, et al. [16] for low

temperatures and by Roeser and Lonberger [13] for high temperatures.

Estimates of errors caused by poor thermal insulation or tempering can

be calculated using standard heat transfer equations. An important

physical parameter necessary for those heat transfer calculations is the

thermal conductivity. Values of the thermal conductivity have been

compiled by Childs, et al. [17] for low temperatures and by R. W. Powell,

et al. [18] for high temperatures.

Values for other physical parameters of platinum are contained in

standard handbooks and in two corporate publications by International

Nickel Co. [19] and Engelhard Industries, Inc. [20].

4. LOW-TEMPERATURE THERMOELECTRIC MEASUREMENTS

For any calibration experiment, whether it be at high or low temperatures, it is very important that the experimental method incorporate

sufficient redundancy for meaningful statistical analyses. Unfortunately,

this fundamental requirement is often overlooked. There are many ways

in which statistically important comparisons may be incorporated into an

experimental methodology. One of the simplest yet most powerful, was

suggested by Youden [21] some years ago. The general method has been

greatly expanded and made more rigorous utilizing the mathematical

concepts of network or graph theory and the specific use of connectivity

in those graphs [22,23]. Those developed methods have been incorporated

into our publications on thermoelectric thermometry (e.g., 1,2). They

were also used for the thermoelectric measurements reported in this

Special Publication. Because of their importance to the reliable and

accurate usage of this Standard Reference Material, an outline of their

application to a simple four object measurement is described next.

As a simple illustration of how graph theory is applied, consider

the situation where one is to intercompare some property of two different

objects where two other intermediate objects are also available.

Graphically this situation can be represented as in figure 2. In this

figure, the objects are represented by the vertices and the comparison

11
of some property between objects is represented by the connecting lines.

For example, the comparison a might represent the difference in weight

between objects A and B. In applying graph theory to thermoelectric

measurements, the vertices represent the thermocouple test wires and the

connecting lines represent the thermal voltages generated by a given

temperature gradient. The thermoelectric voltage between A and C in

figure 2 would be determined by (1) measuring o, that is, a direct

measurement of the desired voltage, (2) measuring the thermal voltages a

and b and combining these data algebraically, and (3) measuring the

thermal voltages d and e and similarly combining these data. The algebraic

combination of a + b and d + e yield two additional independent determinations of the desired voltage equivalent to a. The final determination

of the voltage (A-C) is given by:

e - = (A-C)= [2&+(a+b)+(d+e)]/b. (1) oaLo

The measurement a is given a weight of 2, since it involves only one experimental determination, whereas the other two measurement paths both

require two readings. The estimate of the variance for (A-C) is given

by

:

^ealc-^l

2

}' 3 - < 2 >

v The advantages of taking data in this way are that it randomizes potentiometer dial or multimeter output errors, eliminates any subconscious

operator prejudice, and randomizes spurious voltages in the lead wires.

The magnitudes of a, b, c, d, and e usually vary considerably; this means

that the potentiometer dial or multimeter settings are also considerably

different. Any setting errors which exist are randomized by this method.

These random errors would then appear as scatter in the data and would

be accounted for in the variance calculated from equation 2.

Since the potentiometer or multimeter readings vary a great deal

and the order of readings may be random, the chance for subconscious

operator prejudice is minimized. In order to influence the readings in

a systematic way, the operator would have to algebraically combine very

different numbers which are not necessarily taken in adjacent readings.

This is not done subconsciously, even on the simple four object system

being considered here. On the other hand, if multiple readings are

taken of the same quantity, there is a strong tendency to produce data

which are biased in a systematic way that falsely reduces the apparent

imprecision.

Spurious voltages in the extension wires are also randomized by

using the graph theory method : Consider a three wire system such as

that which would result if the D wire were eliminated from figure 2.

Assume the number we actually want is (B-C) . This is the thermoelectric

voltage generated by the thermocouple made from materials B and C when

a thermal gradient, AT = Tj_ - T2, exists. The number which is actually

measured is b which includes the spurious voltages generated in the

12
<

13
extension wires to both B and C. If the spurious voltages 6^ and 6 ^ are zero or are at least known, then the true value of (B-C) may be

determined. The voltages 5_. and 6_. can be determined by an isothermal

test where T = T . When T = T~, (B-C) = 0 and b = (B-C) + 6 . + 6 . =

6 r* _L Z _i_ Z Ox* B% C%

However, this determination of the spurious voltages is valid only when

the thermal gradients in the system are the same as when the isothermal

test was made. In many experimental situations this approach to the

spurious voltage problem is not practical. The only other solution is

to randomize these voltages so that they appear as scatter in the experimental data and are therefore included in the estimate of the

variance, s^. The graph theory approach does allow these voltages to be

randomized. Suppose, for instance, that we wish to determine (B-C) in

figure 2. The voltages a3 b3 and a would then be measured.

a = {B-A) + 8A i+8Bl

b = (B-C) + 8B2 +8C i

C=(A-C) + 8A 2+8C2

26+a+c

&dc=[&+*(a+c)]/3/2

^calc =

3

[2(B-Q+(B-A) + (A-Q]

+

3

If the spurious conditions are stable, i.e., the measurements are made

rapidly enough that the system gradients haven't changed,

then 8a = 8ai = 8a2, 8b = $bi— 8B 2, and 8c = Sci = 802

and oca ic= g

+§8A +8B + 8 C. If the more common procedure of multiple readings of b were used, b would

be measured, say, 3 times:

b l = (B-C) 1 -\-8B +8c,

b 2 = (B-C) 2 +8B1 +8cu

6 3 = (5-C) 3 +6b2 +5c2, and

l _ [(B-Qi+(B-Qa +(B-Qi ] "calc — ~

1 8B + Scrh 8bi+ 5ci+ 8B2 + 8 C2

3

Again, assume stable spurious conditions for the time required to determine

b three times. Then 8b = 8Bi=8b2, 8 c =8c1 = 8 C2, and beaic =(B-C)i,2,3+8s+8c.

14
The tendency to randomize dial errors and to eliminate operator

prejudice is illustrated by comparing hQa i 0 from the graph theory method

and from the multiple readings method. More dials or output readings are

probably changed in determining (B-C) 3 (B-A) , and (A-C) than are changed

in determining (B-C) three times. The subconscious operator prejudice

is reduced by having to combine the two readings (B-A) and (A-C) to get

the independent determination of (B-C) .

The third and perhaps the most important advantage of the graph

theory approach to the measurement of thermocouple outputs is the randomization of spurious voltages in the extension wires. These errors

would not be accounted for, i.e., they would introduce a systematic

bias, if the multiple reading approach is utilized. This is shown in

the calculation of the estimate of variance for the two methods

now assume that the only cause of variation is the spurious voltages

First by graph theory:

[2(B-Q + (B-A) + (A-Q]

3

+

3

S

2j..,.= {2(6caic-6) 2 +[6c.io-(o+c)] 2 }/2;

!6oa.c=l/3(5A- + ^-5c0 2

where 8A' = 8A i+8A2,

8b' = 8bi~ and

8c = 8ci~ 8c2-

If spurious conditions are constant, §B, =o, 5c =0 and S

2bc&lc = 1/35^,2.

+

fta+ 5c~\- 831+801+ 8b2+8c2

3

S

260al0 = { (6calo - bi) 2 + (feealc ~ 6S)

2 + (kale ~ &l)

2

} /2

again assuming all scatter is due to spurious voltages, e.g

(B-C) i = (B-C) 2 = (B-C) 3) then

18 S

2

i = [—2(8b~\- 8c)-*r 8bi~\- 8ci~\- 8b2~\~ 802]

+ [-2(8bi+8ci) + 8b+Sc+8b2+8c2] 2 + [-2(8b2+8 C2+8b+8c+8bi+8ci] 2

.

15
Now if the spurious conditions are constant

= = ^o. 6 = 6 = 6 „, and S? . =0.

B Bl B2 c cl c2 bcalc

The spurious voltages do not appear in the estimate of the standard

deviation when the multiple measurement method is used. They are truly

present but unaccounted for until some estimate of systematic error is

introduced.

In other words, the calculated standard deviation using graph theoretical

methods is usually larger than that obtained using simply repeated measurements. However, it is much more representative of the true experimental uncertainty. Likewise, calculated values for quantities such as

the voltages a, b, or c are more representative of their true mean

values. The method also has the twin advantages of spot-lighting erroneous

readings when they do occur and allowing substitution values to be inserted into the data sets when some value is obviously in error or is lost.

4.1. Thermocouple comparator

The thermocouple comparator to be discussed here is basically a

mechanical support which allows thermoelectric intercomparison between

standard reference wires and a test wire without damaging the reference

wires. Figures 3a and 3b show the essential details of the design used

here; complete details are given in a preceding publication in this series

[10] . The two tubes containing the test and standard specimens are dipped

into reference baths, e.g., liquid helium, liquid nitrogen, ice slush

mixture, etc. For the thermoelectric results presented below, Table 4, the

two legs were inserted into liquid nitrogen boiling at atmospheric pressure

and an ice slush and water mixture at 0 °C. Figure 4a is an electrical

schematic of a two wire differential thermocouple. Figure 4b extends the

same configuration to a four wire system such as the one we use in our

thermoelectric comparators. All thermoelectric combinations are accounted

for in the six measurements indicated in this figure. Using graph theory

[1] and thermoelectric additivity principles [24,25], one can get four

independent determinations of any thermocouple pair; e.g., if is

needed, each of the following equations represent a nonredundant , independent determination of E,,,.. :

(6) E

T1

= E

T1

(3) E

T1

= E

T2

" E

12

(3) E

T1

= F - N?3

E

13

(2) E

T1

= E

T3

" E

12

-

" E

23

The relative weighting, assuming the same variance for each measured

voltage, is shown in parenthesis before each equation. The average

value of E is given by:

16
Fig. 3a. Details of thermocouple comparator (pictorial view).

17
•Electrical

connector

Test wire

Expansion

loop -

Reference wires

( Separate Tubes)

6' Long, 32 AWG copper

Instrumentation wires

in one flexible tube.

Reference wires

Test wire

(Separate Tube)

All wires in separate tubes.

Wound on plastic

collar (one layer)—

Wires wound on plastic collar in seperate

layers with plastic tape between layers

Wires soldered into brass

with Wood's metal ( after assembly is complete).

Junctions soldered and insulated from

each other and brass by layers of plastic

tape secured by wire bands

Low melting

point solder

( both ends)

Fig. 3b. Details of thermocouple comparator (wiring diagram).

18
Table 4. Thermoelectric Voltage of Pt-67 versus commonly used

thermocouple wire between liquid nitrogen (76 K) and

the ice (273.15 K) fixed point.

Thermocouple

KP or EP** vs Pt-67

TP** vs Pt-67

Pt-67 vs TN**

Pt-67 vs KN**

Pt-67 vs SRM 733tt

EMF, y V*t

3401.0

207.6

5350.0

2445.1

221.9

++

0.5

0.5

0.5

0.5

0.5

Sensitivity at 76K (uV/K)

5.4

4.3

20.4

10.4

6.2

The data for Pt-67 versus KP, KN, TP, and TN were computed from earlier

data by Sparks et al. [1] and more recent comparisons of the thermoelectr

voltage of Pt-67 and the platinum wire used in [1]. The value for Pt-67

versus SRM 733 was obtained by direct comparison in the Pt-67 comparator

discussed in this paper.

fThe uncertainties given are twice the estimated standard deviations.

** EN or TN A copper-nickel alloy, constantan, Cupron [40], Advance

[41], Thermo Kanthal JN [42].

KP or EP A nickel-chromium alloy, Chromel [43], Tophel [40], T-l

[41], Thermo Kanthal [42].

KN A nickel- aluminum alloy, Alumel [43], Nial [40], T-2 [41],

Thermo Kanthal [42]

.

TP Copper, usually electrolytic tough pitch.

The use of trade names does not constitute an endorsement of any manufacturer's products. Any materials manufactured in compliance with

established standards are equally suitable.

tt SRM 733 is a Ag_-28 at % Au alloy,

in [101.

This SRM is described in detail

19
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E

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T3

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12 - E^l/U.

It is suggested that similar data be taken with different immersion

depths so that different sections of the wires are exposed to the temperature gradient at the liquid-gas interface. Also, repeat data should

be taken with the legs of the comparator reversed in the fixed point

baths. These redundant data are necessary to obtain a value for the

degree of scatter (variance) caused by spurious signals.

The determination of the thermoelectric voltage of a test wire with

respect to the standard reference thermocouple wire is summarized below:

(1) Record the six voltages illustrated in figure 4b.

(2) Repeat step 1 for three immersion depths to randomize spurious

voltages

.

(3) Repeat (1) and (2) with comparator reversed in the baths.

(4) Compute the most probable values of the six sets of six voltages

using all of the redundancy in the data, both for the forward

and reverse directions.

(5) Compute the average voltage for the test wire with respect to

the reference standard:

E

TR

= (En

+ EK+ E

T3 y 3 + (En

+ EM+ ^)R

/3]/2.

Also calculate the variance of this voltage. This variance is based

upon the random scatter indicated by the redundancy of these measurements

The values E-^* E^3, and E23 , similarly determined, are used to

detect possible systematic changes among the reference wires. Control

charts of E^2» ^13 » anc^ E 23 wiH be maintained to detect such changes in

the comparators. To further reduce the possibility of undetected changes

in reference wires, three comparators have been built. The first or

working standard will be used for routine testing; the second or primary

standard will be used occasionally for comparison to the working comparator. The third comparator will be considered as a replacement for

either of the others. Occasional intercomparisons will be made among

all three comparators. Figure 5 illustrates the present intercomparisons

of these three comparators between 76 and 273 K. These measurements

were made on a common transfer wire; the transfer wire was annealed at

1100 °C before each measurement.

The procedure used to prepare the Pt-67 wires for test in the

thermoelectric comparators is as follows: degrease the wire in freon,

rinse in distilled water, and then anneal. The effect of annealing

temperature was investigated by performing thermoelectric comparisons on

wires annealed at 400 °C, 1100 °C, and 1200 °C. The anneals at 1100 °C

and 1200 °C are obtained by passing on electrical current through the

22
specimens and thereby resistance heating them. A thermoelectric difference of 0.41 yV was observed between the wires annealed at 400 and

1100 °C. No difference was observed between the 1100 and 1200 °C anneals.

The 1100 °C anneal, adopted for use to prepare this thermoelectric

standard, is as follows: resistance heat in air to 1100 °C, hold for

four minutes, cool to room temperature in about 2.5 minutes. Slow

cooling of the wire is necessary in order to minimize quenching in

vacancies. This annealing procedure produces wires which are indistinguishable from each other and are apparently strain free since they

are thermoelectrically the same as wires annealed at 1200 °C for a

significantly longer time.

The five wires which were chosen to represent the entire lot of Pt67 and were previously characterized by RRR measurements (see figure 1)

were compared to the standard reference wires in the working comparator

between 76 and 273 K. These results, illustrated in figure 6, show that

no systematic variation in thermoelectric voltage is detectable along

the entire length of Pt-67. Variation of the Seebeck coefficient (dE/dT)

caused by material variability is thus within the measurement error of

the system, approximately 0.002 uV/K.

The cryogenic comparators were designed and will be maintained in

the Cryogenics Division by one of the authors (L.L.S.).

5. HIGH-TEMPERATURE THERMOELECTRIC MEASUREMENTS

The high-temperature comparator is very similar in concept to the

low-temperature one described in the previous section. The schematic

drawing, figure 7, shows the apparatus designed and used by members of

the Temperature Section, Heat Division of the National Bureau of Standards

in Gaithersburg , Maryland. The main conceptual differences in the

techniques are that the high- temperature method uses repeated measurements

rather than graph networks for statistical redundancy and the high

temperature furnace has variable temperatures which must be determined

by reference thermocouple thermometers. The more apparent differences

are that the high temperature specimens are held horizontally rather

than vertically and the electrical switching circuit is different because

of the different type of data redundancy.

The high temperature methodology is also, quite naturally, very

similar to that used at low temperatures. The platinum test wires are

washed with ethanol and are not etched with any cleaning acid. They are

then annealed at 1200 °C in air for 10 minutes, cooled over a 1 minute

period to 750 °C where they are held for 30 minutes. If the material is

part of a Type S or R thermocouple, it is annealed first at 1450 °C for

45 minutes and then cooled to 750 °C and held there for 30 minutes. In

both circumstances the wire is heated electrically by an ac current that

flows through the wires from temporary clamps attached near the ends of

the wires. The annealing is performed in a cabinet to reduce the

effects of variable air currents and possible dust contamination.

23
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The annealed wires, usually about one meter long, but at least 60

cm, are threaded through single bore high purity alumina tubes that are

about 40 to 50 cm long. Care must be exercised during threading to minimize the effects of work hardening. At least one Type S positive thermoelement (Pt-10% Rh) is also assembled with each test batch of platinum

thermoelements so that the test temperature can be determined. Up to

six tubes and wires (including any Type S or Type R positive material

being calibrated at the same time) are then inserted into a larger (18

mm o.d.) alumina tube for further protection. All of the test wires and

the temperature reference thermoelement are welded together at the end

that will be immersed in the furnace. In order to reduce the effects of

variable temperature gradients and cooling of the test junction, the

wires are always immersed at least 25 to 30 cm into the furnace and the

welded junction is placed near the center of the furnace. Because of

the welded junction, about 2 to 6 mm of the reference platinum material

is consumed for each calibration run. The end of each wire opposite to

the welded junction is immersed in a reference bath and joined to a wire

that goes to the switch and potentiometer system. The reference bath is

a carefully prepared ice-water mixture contained in an insulated glass

vessel. Each test wire and its connecting lead wire are inserted in a

separate small glass tube that contains some mercury in the bottom for

electrical contact. Each tube with its wires is inserted into the ice

bath reference and a cover is placed over the reference bath to minimize

the effects of radiation and air convection.

Calibration tests are run at many different temperatures, but the most

common are near the freezing points of antimony, silver, and gold (630.74,

961.93, and 1064.43 °C respectively). It usually takes about one-half hour

for a suitable thermal equilibrium to be obtained by the furnace and thermoelement system. The test temperature is determined by the incorporated

calibrated Type S thermocouple as measured by a potentiometer system. When

the calibrated thermometer indicates the proper temperature, the voltage of

the test thermoelements is measured by another potentiometer system.

As indicated above, a small amount of the reference platinum thermoelement is consumed for each calibration run. In order to prevent the

complete depletion of the primary Pt-67 (SRM 1967) material,, secondary

reference wires are used for the routine calibrations. The secondary

materials calibrated against the primary lot. In this manner the primary

material should be maintained for many years, yet all calibrations are

traceable to the primary Pt-67 material. The primary reference material

is maintained by G. W. Burns of the Temperature Section in NBS, Gaithersburg.

The International Practical Temperature Scale of 1968, labeled IPTS68, uses a platinum-10% rhodium versus platinum thermocouple (Type S) as

the interpolating standard for the temperature range from the antimony

freezing point, 630.74 °C, to the gold freezing point, .1064.43 °C, with

the silver freezing point, 961.93 °C, serving as an intermediate defining

fixed point [6]. Discussions of the development of that scale were

given by Preston-Thomas [26] and Bedford [27] at the Fifth Symposium on

Temperature in 1971. Graphs of the thermoelectric voltage, Seebeck

coefficient and its temperature derivative for the Type S thermocouple

25

are shown in figures 8, 9, and 10 (from reference 2). The circles

indicate fixed point values, not experimental measurements. It is seen

in Fig. 10 that the Seebeck derivatives in the temperature range from

630.74 to 1064.43 °C do not fit smoothly with those in the ranges above

and below. Those deviations are caused by the arbitrary assignment in

IPTS-68 of quadratic behavior to the thermoelectric voltage of Type S

thermocouples

.

It could well be expected that those discontinuities in slope at

630.74 and 1064.43 °C and the imposed quadratic behavior within the same

temperature range would lead to observed differences between IPTS-68 and

other thermodynamic or interpolating scales. Such a phenomenon has been

observed and is becoming well documented. Quinn, et al. [28] and Bonhoure

[29] have compared the thermoelectrically maintained IPTS-68 to radiation

photoelectric pyrometer measurements. These authors clearly observe

significant differences, becoming as large as 0.5 °C near 800 °C. To a

lesser extent, the radiation measurements of Bonhoure [29,30] also

question the thermodynamic temperature assigned to the silver and gold

freezing points.

At the lower temperature reference point, 630.74 °C, the platinum

thermoelectric scale joins the scale where interpolated temperatures are

obtained by platinum resistance thermometers. The use of such thermometers

has been exhaustively described in the recent Monograph by John Riddle

and his colleagues of the Temperature Section [31] . Evans and Woods

[32] have extended platinum resistance measurements from the antimony

freezing point up to the gold point, 1064.43 °C. They also, as could be

expected, find significant differences between the IPTS-68 temperatures

and those derived by assuming a smooth variation of the electrical

resistance of platinum. Their observed deviations, up to about 0.5 °C,

agree qualitatively, and even semi-quantitatively , with those reported

later by Quinn, et al. [28] and Bonhoure [29] using the completely

different radiation technique.

The differences between temperatures based on the IPTS-68 platinum

thermoelectric scale and the true thermodynamic scale can become important

for highly accurate thermometric or thermodynamic measurements. These

considerations will, however, not affect the use of platinum as a reference

thermoelement for other thermocouple materials besides Types S and R

platinum-rhodium alloys. Articles by Jones [33] and by McLaren and Murdock

[34] describe in great detail the precautions one must make to obtain

highly accurate thermoelectric measurements with platinum materials at high

temperatures

.

6. EFFECTS OF IMPERFECTIONS

The thermoelectric voltage of platinum, like most other electronic

properties of pure metals, is more sensitive to impurities at low temperatures than it is at high temperatures. For that reason, pure platinum is

not suitable as a thermoelectric Standard Reference Material below about

50 K. Therefore, SRM 1967 is not recommended for calibrations below the

liquid nitrogen normal boiling point, 77.348K or -195.802 °C. In its

27
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place the Ag-Au alloy, SRM 733, is recommended for use down to the liquid

helium normal boiling point, 4.2K. Deviations of the voltages of three

standard Pt-67 specimens are shown in figure 5 and of five specimens in

figure 6. It is seen that the deviations range from 0.1 to 0.5 yV for

extremely carefully handled specimens with junctions at the ice point and

at the liquid nitrogen normal boiling point. More recent results on two

platinum Pt-67 wires mounted in a cryostat have been obtained by Burley, et

al. [35] in their study on Nicrosil and Nisil alloys. The deviations shown

in figure 11 indicate the amount of variation that can be observed in

practical cryostats, even when great care is used in handling well-annealed

specimens. The errors are larger near 0 °C because the reference bath was

near 76 K and therefore there were larger thermal gradients for the

higher temperature runs.

Vines [36], Rhys and Taimsulu [37], Cochrane [38] and Aliotta [39]

have studied the effects of dilute or trace impurites on the hightemperature electrical properties of pure platinum. Cochrane 's paper is

thorough and up-to-date, especially in its discussion on Pt-67. He

concluded, among many things, that the principal cause of thermoelectric

inhomogeneities was radial chemical inhomogeneity caused by surface

contamination, especially of iron, during the production process. The

thermoelectric effectiveness of some impurities was found to depend on

the melting and annealing of test specimens. The effect of an individual

impurity was essentially linear and the total effect of all impurities

was simply additive from the effects of each specific impurity. All

impurities show a positive effect on the thermoelectric voltage except

gold, which shows a slight negative effect. The largest specific

effects for significant impurities (in yV/ppm weight) are shown by

chromium, lead, silicon (if electrically active) and ruthenium. Because

the iron concentration is usually much greater than that for any other

impurity, the impurity effect on thermoelectric voltage is controlled

primarily by the iron content. Cochrane [36] also includes much data on

the relation of thermoelectric voltage to temperature coefficient of

resistance between 0 and 100 °C.

The effects of impurities on the electrical properties of platinum

at high temperatures are summarized in table 5 and figure 12, both of

which are derived from Cochrane's research [38].

7. RECOMMENDATIONS FOR USAGE

SRM 1967 is intended for use as a standard reference thermoelement from 77K (-196 °C) up to 2040 K (1767 °C) . However, great

caution must be exercised if it is to be used above 1200 °C. The material may be used as (1) a reference thermoelement for calibration of

various thermocouple materials; (2) the negative leg of the standard

thermocouple (Type S) in the IPTS-68 defined temperature range from

630.74 to 1064.43 °C; or (3) the negative leg of Type S or Type R

thermocouples in their temperature range from -50 °C to near the melting

point of platinum.

31
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L diD 1c 5. Effects of impurities

platinum.

on the electrical properties

Effect on Voltage

,

uV/ppm

1

Effect on Resistance, 10

^

Element

Ir

Weight

0.350

Atomic

0.344

Weight

0.200

Atomic

0.197

Pd .069 .038 .100 .054

Rh .200 .106 .090 .047

Ag .025 .014 .150 .083

Cu .115 .037 .349 .114

Fe 2.300 .658 1.280 .366

Ni 0.499 .150 0.160 .048

Cr 4.041 1.077 3.250 .866

Mn 0.322 0.091 0.212 .060

Pb 2.999 3.178 .900 .956

Au -0.070 -0.071 .070 .071

Ru 1.099 .570 .250 .129

Si 1.173 .169 .550 .079

Co 0.161 .049

Os 1.955 1.906

Ta 0.920 0.853

rte 3.680 3.513

W 2.645 2.493

Mo 3.680 1.810

Change in microvolts with the reference junction at 0 °C and the test

junction at 1200 °C.

Change in resistivity coefficient, alpha, the temperature coefficient

of resistance a = (R(100 °C) - R(0 °C))/100 R(0 °C)

.

33
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34
The proper usage of platinum as a thermoelectric standard requires

(1) the availability of highly-characterized, high-purity material; (2)

careful annealing and handling techniques for the material; and (3) an

accurate experimental methodology. The first requirement is satisfied

by the certification of this SRM 1967. The second and third requirements

are discussed next.

7.1. Annealing and handling

The recommended procedure for preparing a Pt-67 standard reference

wire is:

1. Clean with ethanol and air dry.

2. Suspend wire in clean, dust-free cabinet and connect to a

current source.

3. Continuously increase the current until the wire is at about

1373 K.

4. Maintain this temperature for 10 minutes.

5. Slowly decrease the current until the temperature of the wire

is just below incandescence, hold for 60 minutes and slowly cool to room

temperature

.

6. Care should be taken at all times to avoid unnecessary mechanical

stresses of the wire. If the platinum is to be used at high temperature,

use special gloves or paper padding while handling.

7. High-purity sintered alumina tubing is recommended for insulating

and protecting the platinum wire during use at high temperatures. After

assembling the wire in an insulating tube, reanneal the assembly in a

furnace for 60 minutes at 1100°C, followed by slow cooling to room temperature.

If the wire is to be used above 1100 °C, then the annealing temperature should be correspondingly raised. Bedford, et al. [8] recommend

holding the wire at the higher temperature for 30 minutes, then reannealing

the experimental thermocouple assembly in protection tubes at 1100 °C for

60 minutes. The other steps remain the same.

7.2. Experimental methodology

For any temperature range, the general principles discussed by

Roeser and Lonberger [13] should be observed. For cryogenic usage,

Hust, et al. [16] describe methods for thermocouple thermometry; for

high temperatures, the problems and precautions described by Jones [33]

and McLaren and Murdock [34] should be carefully considered.

It should be emphasized again that temperature measurements determined

with Type S thermocouples in the temperature range from 630.74 to 1064.43

°C are based on the defined quadratic thermoelectric behavior imposed by

the IPTS-68. There are probably significant (0.5 °C) differences between

the IPTS-68 scale and best estimates of thermodynamic temperatures in this

temperature range. For accurate thermophysical measurements, results

should be presented in terms of the IPTS-68, but corrections based on the

work of Evans and Wood [32] or Quinn, et al. [28] may be necessary to

obtain smoothly varying property values.
Platinum thermoelements and Types S, R, or B thermocouples have

environmental restrictions when used at high temperatures. They should not

be used in reducing atmospheres, nor in those containing metallic vapor

(such as lead or zinc), nonmetallic vapors (such as arsenic, phosphorous,

or sulfur) or easily reduced oxides, unless suitably protected with nonmetallic protecting tubes. They should never be inserted directly into a

metallic primary tube.

\ Platinum thermoelements that conform closely to the high temperature

values may not necessarily conform closely at cryogenic temperatures,

especially near 77 K. If they are to be used for accurate measurements

both above and below 0 °C, then the materials should be calibrated against

carefully maintained Pt-67 specimens in both temperature ranges.

7.3. Availability

SRM 1967 (Pt-67), issued as 24 AWG wire (0.51 mm diam.) in multiples

of 1 meter length up to a maximum of 3 meters length, may be ordered

from the Office of Standard Reference Materials, Chemistry Building,

National Bureau of Standards, Washington, D.C. 20234. (Longer continuous lengths in multiples of 3 meters can be obtained by special

order to the OSRM.)

8 . ACKNOWLEDGMENTS

We would like to thank R. E. Michaelis of the OSRM for his constant

support and encouragement of this program. This publication could not

have been prepared without the continued helpful cooperation and suggestions of members of the Temperature Section, in particular, G. W.

Burns, J. F. Evans, L. A. Guildner, J. F. Schooley, and M. G. Scroger.

The total program on platinum was very generously supported by the

efforts of scientists from the manufacturing firms, especially B. Brenner,

J. Cochrane, A. V. Lincoln, and E. Zysk.

36
9. REFERENCES

[1] Sparks, L. L., Powell, R. L., and Hall, W. J., Reference Tables for

Low-Temperature Thermocouples, Natl. Bur. Stand. (US), Monograph 124,

56 pgs (US Government Printing Office, Washington, D.C. 20402)

(June 1972).

[2] Powell, R. L., Hall, W. J., Hyink, C. W. , Jr., Sparks, L. L., Burns,

G. W. , Scroger, M. G., and Plumb, H. H. , Thermocouple Reference

Tables Based on the IPTS-68, Natl. Bur. Stand. (US) Monograph

125, 401 pgs (US Government Printing Office, Washington, D.C. 20402)

(1974)

.

[3] Shenker, H. , Lauritzen, J. I., Jr., Corruccini, R. J., and Lonberger,

S. T., Reference Tables for Thermocouples, Natl. Bur. Stand. (US)

Circ. 561, 84 pgs (April 1955).

[4] Roeser, W. F., and Wensel, H. T., Reference Table for Platinum to

Platinum-rhodium Thermocouples, J. Res. Natl. Bur. Stand. (US)

10, 275-279 (1933).

[5] Barber, C. R., The EMF-Temperature Calibration of Platinum,

10% Rhodium-Platinum and Platinum, 13% Rhodium-Platinum Thermocouples over the Temperature Range 0-1760 °C, Proc. Phys. Soc

.

63B, 492-503 (1950).

[6] CIPM-Comite International des Poids et Mesures, International

Temperature Scale of 1968, Metrologia _5, 35-44 (1969); Metrologia

12, 7-17 (1976).

[7] Sessions C and D, Fifth Symposium on Temperature, Washington, D.C.

June 21-24, 1971. Published as "Temperature," Vol. 4, Part I, pp.

169-309 (Inst. Soc. Am., Pittsburgh, 1972).

[8] Bedford, R. E., Ma, C. K. , Barber, C. R., Chandler, T. R. , Quinn,

T. J., Burns, G. W. , and Scroger, M. G., New Reference Tables for

Plat inum 10% Rhodium/ Platinum and Platinum 13% Rhodium/Platinum

Thermocouples, Paper A-151, Fifth Symposium on Temperature,

Washington, D.C. June 21-24, 1971. Published as "Temperature," Vol.

4, Part III, pp. 1585-1602 (Inst. Soc. Am., Pittsburgh, 1972).

[9] Wickers, E. , The History of Pt-27, Temperature, Its Measurement and

Control in Science and Industry _3, Part 1, pp. 259-262 (Reinhold

Publishing Corp., New York, 1962).

[10] Sparks, L. L., and Hust, J. G., Thermoelectric Voltage of Silver - 28 at % Gold Thermocouple Wire, SRM 733, Versus Common Thermocouple Materials (Between Liquid Helium and Ice Fixed Points),

Natl. Bur. Stand. (US) Spec. Publ. 260-34, (1972).

[11] Corruccini, R. J., Notes in laboratory notebook "TC Stds 2" dated

9-26-49. The calibrations on Pt reference material are contained

in series of books labeled "Tc Stds." and "Primary Thermocouple

37
Calibrations," maintained by the Temperature Section, Heat Division,

Natl. Bur. Stand. , Gaithersburg, Maryland.

[12] File 463 maintained by the Office of Standard Reference Materials,

National Bureau of Standards, Gaithersburg, Maryland. The summary

in the text is taken from notes, letters, and memoranda kept in

file 463.

[13] Roeser, W. F. , and Lonberger, S. T. , Methods of Testing Thermocouples and Thermocouple Materials, Natl. Bur. Stand. (US) Circ.

590, 21 pgs (1958).

[14] Clark, A. F. , Deason, V. A., Hust, J. G. , and Powell, R. L. , The

Eddy Current Decay Method for Resistivity Characterization of

High Purity Metals, Natl. Bur. Stand. (US) Spec. Publ. 260-39,

(1972).

[15] Quinn, J. T. and Chandler, T. R. D. , The freezing point of platinum

determined by the NPL photoelectric pyrometer, Paper D-23, Fifth

Symposium on Temperature, Washington, D.C. June 21-24, 1971. Published as "Temperature," Vol. 4, Part 1, pp. 295-309 (Inst. Soc.

Am., Pittsburgh, 1972).

[16] Hust, J. G. , Powell, R. L. , and Sparks, L. L. Methods for Cryogenic

Thermocouple Thermometry, Paper A-145, Fifth Symposium on Temperature, Washington, D.C. June 21-24, 1971. Published as "Temperature, 1 Vol. 4, Part 3, pp. 1525-1535 (Inst. Soc. Am., Pittsburgh, 1972).

[17] Childs, G. E. , Ericks, L. J., Powell, R. L. , Thermal Conductivity of

Solids at Room Temperature and Below, Natl. Bur. Stand. (US) Monograph 131, 624 pgs (US Government Printing Office, Washington, D.C.

20402) (1973).

[18] Powell, R. W. , Ho, D. Y. , and Liley, P. E. , Thermal Conductivity

of Selected Materials, NSRD Series-NBS-8, 168 pgs (US Government

Printing Office, Washington, D.C. 20402) (1966).

[19] Anon., Platinum, the Metal, its Properties and Applications,

23 pgs (Int. Nickel Co., Inc., New York) (1968).

[20] Anon., The Physical Properties of the Noble Metals, Engelhard Industries Technical Bulletin 16, 61-85 (1966).

[21] Youden, W. J., Measurement Agreement Comparison, Paper 5.1, Natl.

Bur. Stand. (US) Misc. Publ. 248, 254 pgs (1963).

[22] Tuttle, W. F. , Connectivity in Graphs (Univ. of Toronto Press)

(1966).

[23] Essam, J. W. , and Fisher, M. E. , Some Basic Definitions in Graph

Theory, Rev. Mod. Phys. 42, 271-288 (April 1970).

38
[24] Finch, D. I., General Principle of Thermocouple Thermometry, Temperature - Its Measurement and Control in Science and Industry _3, Part

2, pp. 3-32 (Reinhold Publishing Corp., New York) (1962).

[25] Benedict, R. P., ed., Manual on the Use of Thermocouples in

Temperature Measurement, ASTM Special Technical Publication 470,

249 pgs (Am. Soc. Testing & Matls. , Philadelphia) (August 1970).

[26] Preston-Thomas, H. , The Origin and Present Status of the IPTS-68,

Paper A-l, Fifth Symposium on Temperature, Washington, D.C. June

21-24, 1971. Published as "Temperature," Vol. 4, Part 1, pp. 3-14

Inst. Soc. Am., Pittsburgh, 1972).

[27] Bedford, R. E. , Remarks on the International Practical Temperature

Scale of 1968, Paper A-Z, Fifth Symposium on Temperature, Washington,

D.C. June 21-24, 1971. Published as "Temperature," Vol. 4, Part 1,

pp. 15-25 (Inst. Soc. Am., Pittsburgh, 1972).

[28] Quinn, T. J., Chandler, T. R. D. , and Chattle, M. V., The Departure of IPTS-68 From Thermodynamic Temperatures Between 7 25 °C and

1064.43 °C, Metrologia £, 44-46 (1973).

[29] Bonhoure, J. , Etude Pyrometrique des Temperatures Comprises entre

(630 °C et 1064 °C). Notes to the Comite Consultatif de Thermometrie, Bur. Intl. des Poids et Mesures, Paris, (1974).

[30] Bonhoure, J., Temperature du point de Congelation de L'or. Notes

to the Comite Consultatif de Thermometric, Bur. Intl. des Poids

et Mesures, Paris, (1971).

[31] Riddle, J. L. , Furukawa, G. T. , Plumb, H. H. , Platinum Resistance

Thermometry, Natl. Bur. Stand. (US) Monograph 126, 126 pgs (US

Government Printing Office, Washington, D.C.) (1973).

[32] Evans, J. P., and Wood, S. D. , An Intercomparison of High Temperature Platinum Resistance Thermometers and Standard Thermocouples,

Metrologia 108-130 (1971).

[33] Jones, T. P., A Comparison of Fixed-Point and Intercomparison Methods

of Calibration of Platinum - Platinum Rhodium Thermocouples in

the Temperature Range 0-1064 °C. Paper A-14B, Fifth Symposium on

Temperature, Washington, D.C. June 21-24, 1971. Published as

"Temperature," Vol 4, Part 3, pp. 1561-1567 (Inst. Soc. Am.,

Pittsburgh, 1972).

[34] McLaren, E. H. , and Murdock, E. G. , New Considerations on the Preparation, Properties and Limitations of the Standard Thermocouple

for Thermometry, Paper A-147. Published as "Temperature," Vol 4,

Part 3, pp. 1543-1560 (Inst. Soc. Am., Pittsburgh, 1972).

39
[35] Burley, N. A., Powell, R. L., Burns, G. W. , and Scroger, M. G., The

Nicrosil vs Nisil Thermocouple: Properties and Thermoelectric

Reference Data (to be published as an NBS monograph).

[36] Vines, R. F. , "The Platinum Metals and Their Alloys." International

Nickel Co., Inc., New York) (1941).

[37] Rhys, D. W. , and Taimsulu, P., Effect of Alloying Additions on the

Thermoelectric Properties of Platinum, Engelhard Tech. Bull. 10 , 41-47 (1969).

[38] Cochrane, J., Relationship of Chemical Composition to the Electrical

Properties of Platinum, Engelhard Tech. Bull. 1JL, 58-73 (1970).

Also presented as Paper B-153, Fifth Symposium on Temperature,

Washington, D.C. June 21-24, 1971. Published as "Temperature," Vol.

4, Part 3, pp. 1619-1632 (Inst. Soc. Am., Pittsburgh, 1972).

[39] Aliotta, J., Effects of Impurities on the Thermoelectric Properties

of Platinum, Inst, ad Control Systems, pp. 106-107 (March 1972).

[40] Trademark - Wilbur B. Driver Co.

[41] Trademark - Driver-Harris Co.

[42] Trademark - Kanthal Corp.

[43] Trademark - Hoskins Manufacturing Co.

40
BS-1 14A (REV. 7-73)

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO.

NBS Spec. Pub. 260- 56

2. Gov't Accession

No.

3. Recipient's Accession No.

i TITLE AND SUBTITLE

STANDARD THERMOCOUPLE MATERIAL, Pt-67: SRM-1967

5. Publication Date February 1978

6. Performing Organization Code

AUTHOR(S)

Robert L. Powell, Larry L. Sparks and J. G. Hust

8. Performing Organ. Report No.

PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Worlc Unit No. 2750295

11. Contract/Grant No.

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

Office of Standard Reference Materials

National Bureau of Standards

Washington, D.C. 20234

13. Type of Report & Period

Covered

14. Sponsoring Agency Code

. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 77-29155

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

bibliography or literature survey, mention it here.)

Industry-wide standardization of thermocouple wire depends in part on thermoelectric

comparisons of commercial wires to a standard. In this paper we describe a thermoelectric standard, designated Pt-67, which is available in wire form as a Standard

Reference Material (SRM 1967). High purity platinum meets the requirements of a thermoelectric reference material for temperatures from 77K (-197 °C) up to 2040K

(1767 °C). Thermoelectric voltages, residual resistance ratios, temperature coefficients of resistance, and chemical composition are reported for a high purity,

highly characterized lot of platinum that has been developed as a thermoelectric

standard, Pt-67. A review of the historical development of the material is followed

by characterization data on the material and descriptions of the cryogenic and high

temperature apparatus. The important effects of impurities are also described.

Recommendations and precautions for usage of the reference material conclude the discussion.

1 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 )Chmi ca -\ composition; effect of imperfecti ons ; high purity

platinum; high temperature thermoelectric measurements; low temperature thermoelectri

measurements; platinum; Pt 67; residual resistivity ratio; Standard Reference Materia

temperature coefficient of resistors: thermocouplp;. thprmnpl Prtrir ^tanHarrj

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