PUBLICATIONS A111D7 2576.^

NBS SPECIAL PUBLICATION 260-99

t

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

Standard Reference Materials:

Feasibility Study for the

Development of Standards

Using Differential

Scanning Calorimetry

QC- 100

U57

260-99

1985

Jane E. Callanan, Sandra A. Sullivan,

and Dominic F. Vecchia
Tm he National Bureau of Standards was established by an act of Congress on March 3, 1901. The M 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's technical work is performed by the National Measurement Laboratory, the National

Engineering Laboratory, the Institute for Computer Sciences and Technology, and the Institute for Materials Science and Engineering

The National Measurement Laboratory

Provides the national system of physical and chemical measurement; • Basic Standards

coordinates the system with measurement systems of other nations and • Radiation Research

furnishes essential services leading to accurate and uniform physical and • Chemical Physics chemical measurement throughout the Nation's scientific community, in- • Analytical Chemistry

dustry, and commerce; provides advisory and research services to other Government agencies; conducts physical and chemical research; develops, produces, and distributes Standard Reference Materials; and provides

calibration services. The Laboratory consists of the following centers: The National Engineering Laboratory

Provides technology and technical services to the public and private sectors to address national needs and to solve national problems; conducts research in engineering and applied science in support of these efforts; builds and maintains competence in the necessary disciplines required to carry out this research and technical service; develops engineering data and measurement

capabilities; provides engineering measurement traceability services; develops

test methods and proposes engineering standards and code changes; develops and proposes new engineering practices; and develops and improves mechanisms to transfer results of its research to the ultimate user. The

Laboratory consists of the following centers:

Applied Mathematics

Electronics and Electrical Engineering2 Manufacturing Engineering

Building Technology

Fire Research Chemical Engineering2

The Institute for Computer Sciences and Technology

Conducts research and provides scientific and technical services to aid Federal agencies in the selection, acquisition, application, and use of computer technology to improve effectiveness and economy in Government

operations in accordance with Public Law 89-306 (40 U.S.C. 759), relevant Executive Orders, and other directives; carries out this mission by managing

the Federal Information Processing Standards Program, developing Federal ADP standards guidelines, and managing Federal participation in ADP

voluntary standardization activities; provides scientific and technological advisory services and assistance to Federal agencies; and provides the technical foundation for computer-related policies of the Federal Government. The Institute consists of the following centers:

Programming Science and

Technology Computer Systems

Engineering

The Institute for Materials Science and Engineering

Conducts research and provides measurements, data, standards, reference

materials, quantitative understanding and other technical information funda- mental to the processing, structure, properties and performance of materials; addresses the scientific basis for new advanced materials technologies; plans

research around cross-country scientific themes such as nondestructive

evaluation and phase diagram development; oversees Bureau-wide technical programs in nuclear reactor radiation research and nondestructive evaluation; and broadly disseminates generic technical information resulting from

its programs. The Institute consists of the following Divisions:

Inorganic Materials Fracture and Deformation

Polymers

Metallurgy Reactor Radiation

1 Headquarters and Laboratories at Gaithersburg, MD, unless otherwise noted; mailing address Gaithersburg, MD 20899.

2 Some divisions within the center are located at Boulder, CO 80303. 'Located at Boulder. CO. with some elements at Gaithershurf> MD
Standard Reference Materials:

Feasibility Study for the Development

of Standards Using Differential

Scanning Calorimetry

Jane E. Callanan and Sandra A. Sullivan

Center for Chemical Engineering

National Engineering Laboratory

National Bureau of Standards

Boulder, CO 80303

Dominic F. Vecchia

Center for Applied Mathematics

National Engineering Laboratory

National Bureau of Standards

Boulder, CO 80303

Sponsored by: Office of Standard Reference Materials National Measurement Laboratory

National Bureau of Standards

Gaithersburg, MD 20899

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director Issued August 1985
Library of Congress Catalog Card Number: 85-600567

National Bureau of Standards Special Publication 260-99

Natl. Bur. Stand. (U.S.), Spec. Publ. 260-99, 55 pages (Aug. 1985)

CODEN: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1985 For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402
Preface

Standard Reference Materials (SRM's) as defined by the National Bureau of Standards (NBS) are well-characterized materials, produced in quantity and certified for one or more physical or chemical properties. They are used to assure the accuracy and compatibility of measurements

throughout 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. They are also used extensively in the fields of environmental and clinical analysis. In many applications, traceability of quality control and measurement processes 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.

The 260 Series is dedicated to the dissemination of information on different phases of the preparation, measurement, certification and use 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 measurment processes employed, to judge

the statistical analysis, and to learn details of techniques and methods utilized for work entailing

the greatest care and accuracy. These papers also should 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 concered with the availability, delivery, price, and so forth, will receive prompt attention from: Office of Standard Reference Materials National Bureau of Standards Gaithersburg, MD 20899

Stanley D. Rasberry, Chief Office of Standard Reference Materials

iii
OTHER NBS PUBLICATIONS IN THIS SERIES

Catalog of NBS Standard Reference Materials

(1984-85 edition), Catherine H. Hudson, ed , NBS

Spec. Publ. 260 (February 1984). $5.50* SN003-

003-02558-5.

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). PB 1 68068**

Shultz, J. I., Standard Reference Materials: Methods for the Chemical Analysis of White

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

(July 1965). 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-I1065**

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

Michaelis, R. E., Standard Reference Materials: Homogeneity Characterization of NBS Spectrometric Standards II: Cartridge Brass and LowAlloy Steel, NBS Misc. Publ. 260-10 (December

(1965). COM74-1I064**

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. L., 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 Shoiise, P. J., Standard Refer- ence Materials: Recommended Method of Use

of Standard Light-Sensitive Paper for Calibrat- ing 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. 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 (Certifica- tion 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). COM72-50058**

iv
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). COM74-1 1356** Martin, J. F., Standard Reference Materials:

National Bureau of Standards-US Steel Corporation Joint Program for Determining Oxygen and Nitrogen in Steel, NBS Spec. Publ. 260-26

(February 1971). 85 cents* PB 81176620

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). COM71-50365**

Geller, S. B., Standard Reference Materials: Cali- bration 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 Distri- bution 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 Refer- ence 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 Cooperative Study (SRM 758, 759, 760), NBS

Spec. Publ. 260-40 (August 1972.) COM72-

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). SNO03-OO3-0I278-5*

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). COM74-51185

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

Electrolytic Iron, SRM's 734 and 797 from 4 to 1000 K, NBS Spec. Publ. 260-50 (June 1975). $1.00* SN003-003-0 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* SN003-003-0I48I-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* SN003-003-

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* SN003-003-

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 Materials, Pt.67: SRM 1967, NBS

Spec. Publ. 260-56 (February 1978). $2.20* SN003-003-0 18864

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

States Reference Materials, NBS Spec. Publ. 260-57 (February 1978). $2.20* PB 277173

Barnes, J. D., and Martin, G. M., Standard Refer- ence Materials: Polyester Film for Oxygen Gas

Transmission Measurements SRM 1470, NBS

Spec. Publ. 260-58 (June 1979) $2.00* SN003-

003-02077 Chang, T., and Kahn, A. H. Standard Reference

Materials: Electron Paramagnetic Resonance

Intensity Standard; SRM 2601, NBS Spec. Publ. 260-59 (August 1978) $2.30* SN003-

003-01975-5 Velapoldi, R. A., Paule, R. C, Schaffer, R., Mandel, J., and Moody, J. R., Standard Refer- ence Materials: A Reference Method for the Determination of Sodium in Serum, NBS Spec.

Publ. 260-60 (August 1978). $3.00* SN003-003

01978-0

Verdier, P. H., and Wagner. H. L., Standard Refer- ence Materials: The Characterization of Linear Polyethylene (SRM 1482, 1483, 1484), NBS

Spec. Publ. 260-61 (December 1978). $1.70* SN003-003-02006-I

Soulen, R. J., and Dove, R. B., Standard Reference

Materials: Temperature Reference Standard

for Use Below 0.5 K (SRM 768). NBS Spec. Publ. 260-62 (April 1979). $2.30* SN003-003-

02047-8 Velapoldi, R. A., Paule, R. C, Schaffer, R. Mandel, J., Machlan, L. A., and Gramlich, J. W., Standard Reference Materials: A Reference Method for the Determination of Potassium in Serum. NBS Spec. Publ. 260-63 (May 1979). $3.75* SN003-00 3-02068

Velapoldi, R. A., and Mielenz, K. D., Standard

Reference Materials: A Fluorescence Standard

Reference Material Quinine Sulfate Dihydrate (SRM 936), NBS Spec. Publ. 260-64 (January

1980). $4.25* SN003-003-02 148-2 Marinenko, R. B., Heinrich, K. F. J., and Ruegg,

F. C, Standard Reference Materials: Micro- Homogeneity Studies of NBS Standard Reference

Materials, NBS Research Materials, and Other Related Samples. NBS Spec. Publ. 260-65

(September 1979). $3.50* SN003-003-021 14-1 Venable, W. H., Jr., and Eckerle, K. L., Standard

Reference Materials: Didymium Glass Filters for Calibrating the Wavelength Scale of Spectro- photometers (SRM 2009, 2010, 2013). NBS Spec.

Publ. 260-66 (October 1979). $3.50* SN003-003-

02127-0

Velapoldi, R. A., Paule, R. C, Schaffer, R., Mandel,

J., Murphy, T. J., and Gramlich, J. W., Standard

Reference Materials: A Reference Method forthe Determination of Chloride in Serum, NBS Spec.

Publ. 260-67 (November 1979). $3.75* SN003-

003-02136-9 Mavrodineanu, R. and Baldwin, J. R., Standard

Reference Materials: Metal-On-Quartz Filters as a Standard Reference Material for Spectrophoto- metry-SRM 2031, NBS Spec. Publ. 260-68

(April 1980). $4.25* SN003-003-02 167-9 Velapoldi, R. A., Paule, R. C, Schaffer, R., Mandel, J., Machlan, L. A., Garner, E. L., and

Rains, T. C, Standard Reference Materials: A

Reference Method for the Determination of Lithium in Serum, NBS Spec. Publ. 260-69 (July)

1980). $4.25* SN003-003-02214-4 Marinenko, R. B., Biancaniello, F., Boyer, P. A., Ruff, A. W„ DeRobertis, L., Standard Reference

Materials: Preparation and Characterization of an Iron-Chromium-Nickel Alloy for Microanalysis, NBS Spec. Publ. 260-70 (May 1981). $2.50* SN003-003-02328-1

Seward, R. W., and Mavrodineanu, R., Standard

Reference Materials: Summary of the Clinical Laboratory Standards Issued by the National Bureau of Standards, NBS Spec. Publ. 260-71 (November 1981). $6.50* SN003-003-0238 1-7 Reeder, D.J., Coxon, B., Enagonio, D., Christensen,

R. G., Schaffer, R., Howell, B. F., Paule, R. C,

Mandel, J., Standard Reference Materials: SRM

900, Antiepilepsy Drug Level Assay Standard, NBS Spec. Publ. 260-72 (June 1981). $4.25* SN003-003-02329-9

vi
Interrante, C. G.,and Hicho, G. E., Standard Refer- ence Materials: A Standard Reference Material Containing Nominally Fifteen Percent Austen: te (SRM 486), NBS Spec. Publ. 260-73 (January

1982). $2.75* SN003-003-02386-8 Marinenko, R. B., Standard Reference Materials: Preparation and Characterization of K-411 and

K-414 Mineral Glasses for Microanalysis: SRM

470. NBS Spec. Publ. 260-74 (April 1982). $3.50 SN003-003-023-95-7

Weidner, V. R., and Hsia, J. J., Standard Reference

Materials: Preparation and Calibration of First Surface Aluminum Mirror Specular Reflectance Standards (SRM 2003a), NBS Spec. Publ. 260-75 (May 1982). $3.75 SN003-003-023-99-0

Hicho, G. E. and Eaton, E. E., Standard Reference Materials: A Standard Reference Material

Containing Nominally Five Percent Austenite (SRM 485a), NBS Spec. Publ. 260-76 (August

1982). $3.50 SN003-003-024-33-3 Furukawa, G. T., Riddle, J. L., Bigge, W. G., and

Pfieffer, E. R., Standard Reference Materials: Application of Some Metal SRM's as Thermometric Fixed Points, NBS Spec. Publ. 260-77 (August 1982). $6.00 SN003-003-024-34-1

Hicho, G. E. and Eaton, E. E., Standard Reference

Materials: Standard Reference Material Containing Nominally Thirty Percent Austenite (SRM

487), NBS Spec. Publ. 260-78 (September 1982). $3.75* SN003-003-024-35-0 Richmond, J. C, Hsia, J. J. Weidner, V. R., and

Wilmering, D. B., Standard Reference Materials: Second Surface Mirror Standards of Specular

Spectral Reflectance (SRM's 2023, 2024, 2025), NBS Spec. Publ. 260-79 (October 1982). $4.50* SN003-003-024-47-3

Schaffer, R., Mandel, J., Sun, T., Cohen, A., and

Hertz, H. S., Standard Reference Materials: Evaluation by an ID/ MS Method of the AACC

Reference Method for Serum Glucose, NBS

Spec. Publ. 260-80 (October 1982). $4.75* SN003-

003-024-43-1 Burke, R. W., and Mavrodineanu, R. (NBS retired). Standard Reference Materials: Accuracy in Analytical Spectrophotometry, NBS Spec. Publ. 260-81 (April 1983). $6.00* SN003-003-024-8

Weidner, V. R., Standard Reference Materials: White Opal Glass Diffuse Spectral Reflectance Standards for the Visible Spectrum (SRM's 2015 and 2016). NBS Spec. Publ. 260-82 (April 1983). $3.75* SNO03-003-024-89-9**

Bowers, G. N., Jr., Alvarez, R., Cali, J. P. (NBS

retired), Eberhardt, K. R., Reeder, D. J., Schaffer, R., Uriano, G. A., Standard Reference

Materials: The Measurement of the Catalytic

(Activity) Concentration of Seven Enzymes in NBS Human Serum SRM 909, NBS Spec.

Publ. 260-83 (June 1983). $4.50* SNOO3-OO3-024-

99-6

Gills, T. E., Seward, R. W., Collins, R. J., and

Webster, W. C, Standard Reference Materials: Sampling, Materials Handling, Processing, and

Packaging of NBS Sulfur in Coal Standard

Reference Materials, 2682, 2683, 2684, and 2685, NBS Spec. Publ. 260-84 (August 1983). $4.50* SN0O3-O03-O25-20-8

Swyt, D. A., Standard Reference Materials: A Look

at Techniques for the Dimensional Calibration of Standard Microscopic Particles, NBS Spec. Publ. 260-85 (September 1983). $5.50* SN003-003-

025-21-6 Hicho, G. E. and Eaton, E. E., Standard Reference Materials: A Standard Reference Material

Containing Two and One-Half Percent Austenite, SRM 488, NBS Spec. Publ. 260-86 (December

1983). $1.75* SN003-003-025-41-1 Mangum, B. W., Standard Reference Materials: SRM 1969: Rubidium Triple-Point - A Temperature Reference Standard Near 39.30 °C, NBS

Spec. Publ. 260-87 (December 1983). $2.25* SN003-003-025-44-5 Gladney, E. S., Burns, C. E., Perrin, D. R., Roelandts, I., and Gills, T. E., Standard Reference Materials: 1982 Compilation of Elemental

Concentration Data for NBS Biological, Geological, and Environmental Standard Reference

Materials. Spec. Publ. 260-88 (March 1984). $7.00* SN003-003-02565-8

Hust, J. G., Standard Reference Materials: A Fine- Grained, Isotropic Graphite for Use as NBS

Thermophysical Property RM's from 5 to 2500 K, NBS Spec. Publ. 260-89 (September 1984). $4.50* SN003-003-02608-5 Hust, J. G., and Lankford, A. B., Standard Reference Materials: Update of Thermal

Conductivity and Electrical Resistivity of

Electrolytic Iron, Tungsten, and Stainless Steel, NBS Spec. Publ. 260-90 (September 1984). $3.00* SN003-003-02609-3

Goodrich, L. F., Vecchia, D. F., Pittman, E. S., Ekin, J. W., and Clark, A. F., Standard Reference

Materials: Critical Current Measurements on an NbTi Superconducting Wire Standard Reference

Material, NBS Spec. Publ. 260-91 (September

1984). $2.75* SN003-003-026 14-0 Carpenter, B. S., Standard Reference Materials: Calibrated Glass Standards for Fission Track Use (Supplement to NBS Spec. 260-49). NBS

Spec. Publ.. 260-92 (September 1984). $1.50* SN003-003-02610-7

Ehrstein, J., Preparation and Certification of Standard Reference Materials for Calibration of Spreading Resistance Probes, NBS Spec. Publ. 260-93 (January 1985).

Gills, T. E., Koch, W. F. Stolz, J. W., Kelly, W. R., Paulsen, P. J., Colbert, J. C. Kirklin, D. R., Pei, P.T.S., Weeks, S., Lindstrom, R. M.

Fleming, R. F., Greenberg, R. R., and

Paule, R. C, Methods and Procedures Used at the National Bureau of Standards to Certify Sulfur

in Coal SRM's for Sulfur Content, Calorific Value, Ash Content, NBS Spec. Publ. 260-94 (December 1984). Mulholland, G. W., Hartman, A. W., Hembree,

G. G., Marx, E., and Lettieri, T. R., Standard

Reference Materials: Development of a 1 urn Diameter Particle Size Standard, SRM 1690, NBS Spec. Publ. 260-95 (May 1985). Carpenter, B. S., Gramlich, J. W., Greenberg, R. R., and Machlan, L. A., Standard Reference

Materials: Uranium-235 Isotopic Abundance Standard Reference Materials for Gamma

Spectrometry Measurements, NBS Spec. Publ. 260-96 (In Press).

vii
Mavrodineanu, R. and Gills, T. E., Standard

Reference Materials: Summary of the Coal, Ore,

Mineral, Rock, and Refractory Standards Issued by the National Bureau of Standards, NBS Spec.

Publ. 260-97 (In Press). Hust, J. G., Standard Reference Materials: Glass Fiberboard SRM for Thermal Resistance, NBS

Spec. Publ. 260-98 (In Press). Callanan, J. E., Sullivan, S. A., and Vecchia, D. F., Standard Reference Materials: Feasibility Study

for the Development of Standards Using

Differential Scanning Calorimetry, NBS Spec.

Publ. 260-99 (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 22161.
Contents

Page

List of Tables x List of Figures xi

I. Introduction and Rationale for Study 1 II. Outline of Study 5 III. Part I Variability Study 6 A. Procedures 6 B. Results and discussion 8 C. Summary 16

IV. Part II Calibration Study 17 A. Procedures 17

1. General 17

2. Temperature calibration 18

3. Enthalpy calibration 20

B. Results and discussion 21

C. Summary 26 References 33 Appendix A-l

ix
List of Tables

Page Table 1. Indium properties 6 Table 2. Means obtained in indium variability study 9 Table 3. Fusion temperatures for indium specimens (K) 10 Table 4. Enthalpies of fusion for indium specimens (J/g) 11 Table 5. Mean and standard deviation for replicate runs, in succession,

with no disturbance of the specimen 12 Table 6. Original data for replicate runs, in succession, with no disturbance of the specimen 12 Table 7. Weighing procedure evaluation 13 Table 8. Remount and operator study 14 Table 9. Results for repeat runs with specimens remounted (112) .... 14 Table 10. Contributions to variance; range (foil) 16 Teble 11. Melting points of test materials (K) 17 Table 12. Results obtained in preliminary evaluation of the two-point

temperature calibration 19 Table 13. Transition temperatures (K)--initial run 22 Table 14. Transition temperatures (K)--repeat runs 23 Table 15. Enthalpies of fusion (J/g) 25 Table 16. Summary of transition temperatures and enthalpies 32

x
List of Figures

Page

Figure 1. Deviations from the mean value as reported by the 34 investigators (submitted to the Standards Committee of ICTA) 3 4 Figure 2. Initial and final runs for naphthalene 27 Figure 3. Initial and final runs for acetanilide 28 Figure 4. Initial and final runs for diphenylacetic acid 29 Figure 5. Initial and final runs for anisic acid 30 Figure 6. Initial and final runs for 2-chl oroanthroqui none 31

xi

Feasibility Study for the Development of Standards Using Differential Scanning

Cal orimetry

Jane E. Callanan, a Sandra A. Sullivan, 3 and Dominic F. Vecchia b Center for Chemical Engineering 3 Center for Applied Mathematics*3 National Engineering Laboratory

National Bureau of Standards

Boulder, Colorado 80303

The tremendous increase in the use of differential scanning cal or- imetry, coupled with the decrease in the capability for conventional precision calorimetry, has created a need for more and better thermal standards for use with scanning calorimeters and other thermal instru- ments currently available, such as thermomechanical analyzers. The de- velopment of these standards by methods such as adiabatic or drop cal- orimetry is impractical because of the number and variety of standards

required, the associated expense, and the lack of facilities and per- sonnel to do the certification. A two-part study was designed to evaluate the capability of a differential scanning calorimeter for de- veloping temperature and enthalpy of fusion standards. Part I evaluated the variability of the differential scanning calorimeter (DSC) and factors which affected it; Part II applied American Society for Testing

and Materials (ASTM) procedures for the temperature and heat flow cali- bration. The study shows that fusion standards can be developed with a differential scanning calorimeter.

Key words: differential scanning calorimetry; enthalpy; fusion; pilot

study; standards; temperature; thermal analysis

I. Introduction and Rationale for Study

The last decade has seen a tremendous increase in the number of differential scanning calorimeters (DSC) 1 in use. During this same decade, the number of

*The acronym DSC refers to an instrument; d.s.c. refers to the calorimetric tech- nique.
adiabatic calorimeters available has declined alarmingly. Because of this de- cline many investigators are constrained to use DSCs, but require the maximum ac- curacy and precision possible. A paper to be published shortly in the open lit- erature outlines the prescriptions for use found satisfactory in our labora- tory [1].

Adiabatic (precision) calorimeters use measurements of time, voltage and current, the latter two obtained by use of a calibrated standard cell and cali- brated standard resistor. Construction details and a system of shields largely

eliminate heat transfer to the environment. The quantities required for the de- termination of the heat capacity are measured with great accuracy.

A differential scanning calorimeter consists of twin cups (calorimeters),

circuitry that can produce a linear increase or decrease in temperature of both cups, and a differential circuit that either keeps both cups at the same temperature or evaluates the temperature difference between them. It does not have an electrical calibration heater nor the means to measure (and/or design to minimize) differences in heat leaks between calibration and "unknown" experiments.

As the heat leak is large and somewhat dependent on the environment, standards must be run repeatedly with those scanning calorimeters classified as power- compensated, Boersma differential thermal analyzers (DTA) or DTA instruments.

The DSC is not an absolute measuring instrument; standards must be used as calibrants each time measurements are made. The validity of the results obtained

is dependent on the calibration. Instrumental controls may be adjusted to give

the correct value for the cali brant or the data may be corrected as required by the calibration results. Because of the inherent day-to-day instrumental vari- ability and the time that may be required for instrument adjustment, the most satisfactory procedure is occassional ly to set controls on the instrument to give values close to those in the literature and then to correct data as indicated by

daily calibration checks.

-2-
The reference materials most generally used for differential scanning calor- imeters (DSC) are the Special Reference Materials (GM) distributed by the Office

of Standard Reference Materials (OSRM) as GM 754 and 757-60 [2]. These materials

were developed by the International Conference on Thermal Analysis ( ICTA) in the late 1 960 1 s to allow for comparison among results obtained with instruments of widely-different design; often these were non-commercial, uniquely- constructed

instruments. The materials were not intended to be standard reference materials

in the strict sense. The temperature variations noted in the ICTA certificate

which accompanies GM 758-60, shown in figure 1, are an order of magnitude greater

than those that would be obtained with modern instrumentation [3]. When the DSC is used in the scanning mode, as it is generally, standards be- come particularly important. Compensation for thermal lag is not automatic in the scanning mode, as it is when enthalpic procedures are used [4,5,6]. Therefore it is desirable to have a standard that is similar in nature to the sample being tested, i.e., that will have similar thermal lag. Metallic standards are preferred for studies of metals, organic materials for organics, pow- dered standards or crystalline standards for corresponding materials, etc. In addition, the excellent calibration methods established by the American Society

for Testing and Materials (ASTM) work best when calibrants available are about

50 K apart [7,8].

Several factors led us to attempt to develop new Standard Reference Materials (SRM's) for d.s.c. Instruments commercially available today readily give

an order of magnitude improved precision over the instruments used for the ICTA standards. There has been an explosion in the use of differential scanning calorimetry; thus needs for standards are greater. Present day energy costs require

improved thermal property data. Facilities for obtaining very accurate and

-3-
• • • • •

i:

T

CM 2 a

3 *S338930

-4-
precise calorimetric data are few and far between, and becoming more so [9]. In addition, the cost associated with these measurements is high. For many purposes industry does not need data of the accuracy provided by methods comparable to adiabatic calorimetry. For all these reasons it seemed worthwhile to attempt the relatively inexpensive certification of materials, using d.s.c, which do relate

to thermodynamic equilibrium values.

II. Outline of Study The first part of the study was intended to determine whether a differential scanning calorimeter could be used to develop standards for d.s.c. In certifying

standards the usual practice is to develop the standard with a different method,

preferably an absolute measuring one, such as adiabatic or drop calorimetry. If only one or two standards were required, precision calorimetry would be feasible,

but expensive and difficult. The facilities for making such measurements in the temperature range needed most (300 - 1000 K) are virtually nonexistent or un- available in the United States. Therefore we designed a study of indium fusion

to evaluate the variability inherent in the DSC and our procedures for working

with it, and thus the suitability of a DSC for the development of standards. The judgement regarding suitability was to be based on a statistical analysis of the experimental results; this analysis would consider both total variability and the effects of instrumental and manipulative factors on this variability.

The second part of the study, which will be described in more detail later,

applied ASTM calibration procedures to a selected group of substances. Sub- stances 1 and 3 were used, as bracketing substances, to calibrate the DSC and the transition properties of substance 2 obtained. Then substances 2 and 4 were used for bracketing and the properties of substance 3 obtained. This procedure, fol- lowed through the selected list, would allow us to determine 1) whether the DSC would produce the accepted temperatures satisfactorily and 2) what error is to be expected in various temperature ranges.
III. Part I. Variability Study

A. Procedures

The protocol to be followed was discussed with Karen Kafadar, formerly of the Statistical Engineering Division (714) of the Center for Applied Mathematics,

Gaithersburg [10]. Three forms of indium which were readily available (rod, granules, foil) were used to conduct a five-specimen, four-replicate analysis of the temperature

and enthalpy of transition. Information about the three forms of indium used for the study is given in table 1. In-laboratory measurements of the purity qualitatively reinforced the nominal values.

Table 1. Indium properties

Nominal purity

Form (percent) Granular 99.999

Rod 99.9999

Foil (0.076 mm thick) 99.999

The sixty replicate runs were made in random order. Since it was possible

that variations in mains voltage could affect the results, some samples were run during the normal working day, some during start up and shut down periods, some

in the evening and on weekends. In addition to these sixty measurements, three- replicate measurements were made on six specimens without any operator interference (leaving the specimens in place and rerunning them.) These allowed for the estimation of variability due to the instrument itself. On examination of the results after completion of this work, two short studies were added. One of these was designed to help us separate remount variations from specimen varia- tions; the other allowed for comparison between two experienced operators.

Variations introduced by weighing procedures and in the data analysis pro- gram were evaluated separately.

-6-
The accuracy and precision of the weighing procedure were estimated from ten replicate measurements of the NBS-cal ibrated 50 mg Class M weight; this weight

was chosen as it is close to the mass of the specimens used. All mass determinations were made on a microbalance capable of weighing to tenths of a microgram.

The usual weighing procedure in this laboratory always involves duplicate weighings. If these agree within 5 micrograms, no further weighings are made. A change of 5 yg in specimen mass results in a 0.05% change in the heat capacity of sapphire; a change of 50 yg affects the heat capacity by 0.58%. If there is an unusual variation, which may result from environmental factors, repeated measure- ments are made until reproducible results are obtained.

The automated data acquisition/reduction system uses a Simpson's rule inte- gration routine for determining the area under the peak, i.e., the enthalpy of fusion. Before the integration routine is called for in the data reduction

scheme, the operator must decide, from the scan, where the transition begins and ends, and set cursors accordingly. Cursor judgement variations were determined

as follows. The same scan was used by three observers, each of whom made three evaluations; these evaluations were made at widely-spaced time intervals to at- tempt to rule out bias caused by operator memory.

In attempting to assign relative variances in this study, as initially de- vised, it became obvious that we had no way to separate the variance due to re- mounting the specimen in the DSC from that due to the specimen itself. For this

reason a single specimen was remounted five times. This operation was repeated

by a second experienced operator. For the temperature calibration the instrument was first linearized over the temperature range of the fusion standards by adjustment of appropriate circuitry

incorporated into the instrument. Then, again by adjusting additional controls,

the observed onset temperature of fusion was matched to the literature value for

-7-
that standard. The enthalpy calibration of the instrument was based on an en- thalpic heat capacity determination with sapphire. Temperature and enthalpy mea- surements for the specimens were corrected from day to day as indicated by the fusion standards, which were checked several times during each day of the study. Our instrument was calibrated with an existing indium rod and a new tin standard. On only one day were significant variations in the standard noted; corrections for that day were made on the basis of the time of the calibration

and the experimental run. Because the corrected means obtained for the indium specimens do not agree with the accepted values, it is obvious that the indium

fusion standard needed replacement. But, since the purpose of this work was to study the consistency of results with the calorimeter on a number of specimens,

preparation of a new standard was not considered necessary at the time. The analysis in this report, coupled with information generated in our lab- oratory, allowed for the determination of the significant variables and the mag- nitude of their effects. Results of the analysis are discussed below. An ex- planation of the methods used to account for specimen variability can be found in an appendix to this report.

B. Results and discussion

Table 2 shows the estimated temperature and enthalpy of fusion for each form

of indium. Each estimate is the sample mean of 20 measurements (four repeats from each of five specimens). The standard error of the mean^ is also included

in table 2. Estimated standard errors were computed based on a statistical model that accounts for possible specimen-to-specimen variability. An explanation of the methods that were used to obtain the standard errors and their associated de- grees of freedom can be found in the appendix. For reference the simple standard deviation of each set of 20 measurements, which ignores the grouping of repeat measurements by specimen, is also given in table 2.

2 Standard error of the mean is synonymous with standard deviation of the mean.

-8-
Table 2. Means obtained in indium variability study Mean

K

N Standard Error of Degrees of Standard Deviation Mean* Freedom Temperature

K K Gramd- Mean Granular

Rod

Foil

429.558 429.566

429.509

429.602

602020

20

.083

.038

.036

41919

0.216

0.164 0.159

Enthal py J/g J/g J/g Grand Mean Granular

Rod

Foil

28. 773

28. 623

28. 761 28.936

6020

20

20

.089 .105

.055

4

4

4

0.293

0.322 0.172 *See appendix

Though the DSC reads only to two decimals, a third is retained in reporting

derived results because of information that can sometimes be obtained from it. Tables 3 and 4 list the original temperatures and enthalpies from which table 2 was derived. A five-specimen sampling, used to ensure the proper separation of variables for comparisons made later in this paper, was selected at random from values given for each form in tables 3 and 4. The mean, standard deviation and variance for a five-specimen sampling are shown in these tables also. The variations given in table 2 show the present data to be more precise, by 1-2 orders of magnitude, than the data shown in figure 1. Thus, these results indicate that we can establish the temperature and enthalpy of fusion satisfac- torily for use with differential scanning calorimeters.

Replicate measurements made without operator interference showed a standard deviation considerably smaller than that noted with operator interference. The results of these replicate runs are shown in table 5. In this table, three deci- mals are retained, as earlier, for statistical purposes. The original data ap- pear in table 6. The variance associated with these measurements is referred to

as instrument variance in later portions of this paper.

-9-
Table 3. Fusion temperatures for indium specimens (K) Granular Rod Foil

11 429.63 16 429.50 111 429. 71* 429.96 429.39* 429.60 430.01* 429.40 429.74 429.62 429.58 429.67

12 429.63 17 429.38* 112 429.53 429.34 429.31 429.72 429.72 429.65 429.83 429.32* 429.60 429.45*

13 429.48 18 429.84 113 429.53 429.49 429.46 429.50* 429.41* 429.33* 429.48 429.36 429.30 429.75

14 429.35 19 429.78 114 429.34 429.33 429.37* 429.67 429.38* 429. 75 429. 72* 429.41 429.67 429.45

15 429.64 110 429.56 115 429.81 429.61 429.52* 429.74 429.92* 429.36 429.25*

429.68 429.43 429.54 *Results used for estimation of specimen variance.

Five-Specimen Results Mean + Standard Deviation 429.608 + 0.329 429.552 + 0.220 429.526 + 0.196 Variance 0.108 0.048 0.038

-10-
Table 4. Enthalpies of fusion for indium specimens (J/g) Granular Rod Foil

11 28.70 16 29.20 111 29.08 28.12* 29.12* 29.04

28. 79 28.91 28.91 27.82 28.87 29.00*

12 28.49 17 29.16* 112 29.04

28.91 29.04 28.74*

28.62 28. 56 28.83 28.54* 28.70 29.04

'

13 29.00 18 29.04 113 29.08 28.83* 28.91 29.12 28.95 28.20* 28.95* 28.87 28.95 28.87

14 28.74 19 28.74* 114 29.29*

28.49 28.91 28.83 28.58* 28.20 28.83 28.79 28.95 29.16

15 28. 79 110 28.45 115 28. 79 28 . 70 28.41* 28 . 62 28.45* 28.28 28.87*

28.28 28.45 28.66 *Results used for estimation of specimen variance. Five-Specimen Results

Mean + Standard Deviation 28.504 + 0.257 28.726 + 0.424 28.970 + 0.204 Variance 0.066 0.180 0.042

-11-
Table 5. Mean and standard deviation for replicate runs, in succession, with no disturbance of the specimen

Temperature Enthal py Specimen Mean Standard Deviation Mean Standard Deviation Degrees i K K J/g J/g Freedom Granular

Mean 3 429.565 0.148^ 28.623 0.256 15

14 429.415 0.026 28.480 0.088 3 15 429.653 0.038 28. 70-2 0.031 2 RodMean 3 429.509 0.168 CO •

/

VI nU. C9 7fi i r IKS ID 16 429.42 0.020 28. 815 0.088 2 17 429.337 0.025 29.121 0.109 2 FoilMean 3 429.602 0.170 28.937 0.148 15 112 429.84 7 0.015 28. 732 0.088 2 113 429.505 0.007 29.142 0.029 1 114 429. 740 0.020 29.066 0.025 2

3 These means + deviations refer to procedures in which the specimen was re- mounted in the calorimeter for each measurement. The standard deviations have

been corrected for specimen-to-specimen variability. See table 3 in appendix. TaDle 6. Original data for replicate runs, in succession, with no disturbance

of the specimen

Temperature (K) Enthalpy (J/g) Granular (14) 429.38 28.58 429.41 28.45 429.43 28.41 429.44 28.54

(15) 429.61 28.70 429.67 28.74 429.68 28.66

Rod (16) 429.40 28.91 429.42 28.74 429.44 28.79

(17) 429.31 29.04 429.34 29.08 429.36 29.25

Foil (112) 429.83 28.83 429.85 28.66 429.86 28.70

(113) 429.50 29.12

429. 51 29.16

(114) 429. 72 29.04

429. 74 29.08

429. 76 29.08

-12-
The results of the evaluation of the weighing procedures, table 7, show that

no significant error is introduced by these procedures.

Table 7. Weighing procedure evaluation

Calibration value of mass 49.966 mg Experimental value 49.973 + 0.002a mg

49.972 + 0.001 b mg

a Includes all ten measurements.

b Excludes two measurements outside of our acceptable range. This result fol- lows from our normal weighing procedure.

NOTE: The difference between the calibration mass of the 50 mg weight and the average value obtained here is insignificant when the combined uncer- tainties in the calibration weights and the standard deviation of the in- strument are considered. For a weighing-by-difference procedure such as used in this work, it is customary to use tne combined uncertainties

(0.0022 ng) plus three times the standard deviation.

The reproducibility of the computer analysis procedure, reflected as ana- lytical variance in table 10, was evaluated by having three operators evaluate a single experimental run three times. These analyses were done relatively far apart in time to reduce operator bias introduced by memory. There was no varia- tion in the temperature of transition as a result of cursor settings; the same value, 429.87 K, was obtained in all nine evaluations. For the enthalpy evaluation, the average value for all nine trials was 28.414 + 0.046 J/g, which corresponds to a variability of 0.16%. Two of the operators always obtained the same

value. The third obtained different values which average to 28.380 + 0.063 J/g; this corresponds to a variability of 0.22%. However, this evaluation was in a sense unnecessary as the calibration rou- tine used in this laboratory cancels out systematic error involved in the inte- gration. The random error associated with the integration arises from the same sources as the random error associated with the instrument variation in this

-13-
study. The resulting contribution to the error of the measurements, therefore,

is considered to be included in the instrument error.

The results for the remount and operator study are shown in table 8. The data on which these are based are shown in table 9.

Table 8. Remount and operator study

Operator T(K) Enthalpy (J/g) 1* 429.098+0.144 28.420+0.106

2 429.088+0.134 28.608+0.106

*Primary operator for experimental work in this report.

Table 9. Results for repeat runs with specimens remounted (112)

Operator 1 T(K) Enthalpy (J/g) 428.99 28.41 429.14 28.24 429.14 28.28 429.15 28.28 428.82 28.49 Mean 429.048 28.340 Standard Deviation 0.144 0.106

Mean corrected for 429.098 + 0.144 28.420 + 0.106 daily cal ibration

Operator 2 429.79 28.19 429.01 28.41 428.65 28.16 428.88 28.15 429.89 28.23 Mean 428.844 28.228 Standard Deviation 0.134 0.106

Mean corrected for 429.088 + 0.134 28.608 + 0.106 daily cal ibration

-14-
In order to determine whether time of run or mass of specimen affected the measurements, the temperatures and enthalpies of transition were plotted as a function of these two variables. The time at which the runs were made, either day of the week or time of day, had no correlation with the results. Thus variations in mains voltage do not appear to be affecting instrument behavior. Specimen masses varied from 0.93 - 3.49 mg. No correlation between specimen mass and either temperature or enthalpy

of fusion was observed.

The statistical analysis indicated that somewhat "tighter" results were ob- tained with the foil. In addition, auxilliary information showed that the most serious variations appeared to exist among specimens of the same form, the within-form variations.

In order to get an idea of the contribution of specimen inhomogenei ty to the variance, an analysis of the contributions to the variance, as shown in table 10, was carried out. The range for each variable is also given. For the evaluation

of the analytical variability an existing indium scan was used. All the other variables given in table 10 refer to foil specimens. Specimen 112 was used for remount and operator variability tests. Five results each, both temperature and enthalpy, were selected at random from the results for foil shown in tables 11 and 12 and used to obtain the estimate of total variance for a population of five

in table 10. (The value given in table 2 is for a population of 20.) The (1) and (2) associated with remount variance refer to two different operators.

The total variability had contributions from the instrument itself, S-j , the remounting operation, Sr

, and the specimen, S

s

.

st

2

= s

s 2 + s

r

2 + (1)

-15-
Table 10. Contributions to variance; range (foil)

Range

0.00

0.00

.03 0.33

0.01 0.58

Temperature (K) Variance

(0.00) 2 (0.00) 2

(0.015) 2 (1)(0.144) 2

(2)(0.134)z (0.00) 2 (0.196) 2 (0.133) 2

Enthalpy (J/g)

Degrees

of Freedom

analytical

procedure

instrument

operator TOTAL

specimen

Variance

(0.00) 2 (0.055)2

(0.088) z

(0.106)2

(0.00) 2 (0.204) 2 (0.172) 2

Range

0.00

0.03

0.17

0.25

0.27

S

t is the standard deviation for five starred measurements, shown in table 3. The magnitude of can be determined from results in table 5, repeat runs in place. Results for remounting the same specimen give S r

2 + S^ 2

, table 9. The estimate of specimen variance given in table 10 was obtained by

2 2 2 2 s/ - (S

L + S. ) = S . t r x s For this estimate the remount results for the primary operator were used and

the operator variance omitted. The contribution to the variance from the ana- lytical procedure is included in the other contributions and was not subtracted

separately.

The estimate of specimen variability for enthalpy using this approach differs from that given in table 3 of the appendix, which was obtained using an al- ternate procedure. This difference, 0.02 J, is insignificant for a DSC.

C. Summary

In summary, the total uncertainty in enthalpy, as calculated for the five- specimen results for foil given in tables 3 and 4, was 0.7%; in temperature,

-16-
0.05%. Thus, unquestionably, satisfactory values for SRM's for d.s.c. and other

thermal analysis techniques can be obtained using a DSC in its most precise modes

of operation. Also, metallic samples in foil form gave slightly better uni- formity than rod; foil appears to be significantly better than granular specimens. If, then, materials of equal purity are available for standards develop- ment, foil is the preferable form.

IV. Part II. Calibration Study

A. Procedures

1. General The second part of this study called for an evaluation of the ASTM calibration procedures when used with suitable materials [7,8].

The test materials selected were from the group of melting point standards certified by the National Physical Laboratory (NPL) and marketed in the United

States through OSRM. The materials used and their reference temperatures are given in Table 11.

Table 11. Melting points of test materials ( K) Substance NPL Certificate Values [13] Literature Values Naphthalene 353.37 353.37 [11]

Acetanilide 387.51 387.51 [11]

Di phenyl acetic acid 420.41 420.41 [11]

Anisic acid 456.45 456.14 [12]

2-Chloroanthraquinone 482.75 482.20 [12]

The certificates for these materials indicate that these reference temperatures refer to a specific heating regime, heating at 2 K/min with the specimen

contained in a glass capillary tube. Where other definitive work has been done,

the values are listed in column 3 of table 11.

-17-
We chose to use five specimens of each of these materials and run a four- replicate analysis. This choice was based on the results of the indium study. The specimen sets were randomly selected; within these sets, however, the specimens were run in the order of increasing melting points. The two-point tem- perature calibration procedure recommended by ASTM was followed [7]. The protocol for temperature calibration calls for bracketing the tempera- ture of interest with two known standards and then following the calculations

outlined below. The experimental procedure involved running an indium standard before and after the unknown runs, as well as at intervals in between. The actual number of

indium checks depended on the number of sets of samples run on any specific day.

In fact, the calibration checks were not necessary as the differences between ob- served and literature values are incorporated into the equations. However, as the indium runs are part of our normal procedures, they were made. Enthalpic measurements of sapphire over the pertinent temperature ranges were made so that the ASTM procedures for enthalpy calibration could be applied.

2. Temperature calibration

The calculation of the observed transition temperature was obtained from eq (1) of the temperature calibration protocol,

where T is the actual specimen temperature, T

0 is the observed temperature, S is the slope and I, the intercept. The slope and intercept are calculated from

eqs (3) and (4).

T = (TQx S) + I, (2)

S = (TS

1

- TS

2 )/(T01 - T02

)

I = [(TOj x TS

2

) - (TS

1 x T0

2 )]/(T0

1 - T02

).

(3)

(4)

-18-
A preliminary evaluation of the method was based on results for metallic

specimens chosen at random from existing calibration logs. These results, as well as those from a preliminary study of some organic NPL standards, are shown

in table 12.

Table 12. Results obtained in preliminary evaluation of the two-point temperature

cal ibration

Fusion Temperature (K) Literature Observed

Indium 429. 784

13 429.71

Tin 505. 118

14 504.87

Lead 600. 58

1

5

600.08

Zinc 692. 73 14 692.83 Calculated

In,Pb Sn 505. 13 In.Zn Sn,Pb 504.88, 600.02

Indium 429. 784

13 430.07

Anisic Acid 456.45+0.

11 456.24 2-Chloroanthraquinone 482. 75+0.

3

11 481.83

Tin 505.118

14 505. 74 Calculated

In,Sn AA,2-CL 455.86, 481.83

In,2-CL AA 456.30 AA,Sn 2-CL 482.34 *The values cited as calculated in this table have been obtained using the two substances in the first column as bracketing substances. The materials for which calculated values were obtained are shown in the second column. The calculated temperatures are shown in the third column.

-19-
3. Enthalpy calibration

The enthalpies of transition were determined from the scans by an automated

protocol which was evaluated in the indium study discussed earlier in this re- port. Corrections to the enthalpy were made as recommended in the ASTM Heat Flow Protocol, E968 [8]. This protocol calls for determi nation of the melting iso- therm for one standard material to obtain its enthalpy of fusion.

A calibration coefficient at the fusion temperature is determined from a comparison of the observed enthalpy of fusion with the literature value. This calibration is extended to other temperatures by factors derived from determinations of the heat capacity of sapphire (or another heat capacity

standard) at the reference temperature and temperature( s) of interest.

A few changes were made in the recommended protocol. It was not necessary

for us to make a preliminary run as specified in Note 2 [8] as the automated system is capable of adjusting for deflection. We used a heating rate of 5 K/min rather than 10 K/min as, in our experience, accuracy is improved at lower scan rates. The enthalpic method was used, rattier than a scanning method, to deter- mine the heat capacities for extension of the calibration to other temperatures.

All specimens were run under identical conditions. Argon was used as purge gas,

set at 137.9 kPa gauge (20 psig). The specimen holders were hermetically sealed aluminum pans. Masses were determined on an electronic microbalance accurate to better than 2 pg. For our purpose the peak melting temperature was not necessary; for the equipment and program used, the onset temperature is considered to be the fusion temperature.

Indium foil (99.999% pure) was used as the fusion standard and Calorimetry

Conference sapphire for the specific heat capacity measurements. The latter measurements were made by the enthalpic method over a temperature interval chosen

-20-
so that the temperature of interest was at the midpoint of the run [4-6]. Since our measurement system is automated, the equations specified in the ASTM protocol were not applicable [8]. The equations substituted follow.

The calibration coefficient (E) is obtained from the rat to of tire literature

value of the enthalpy of transition UH^) to- t*»* observed valu* t^^)*

E = AH(lit)/AH(obsJ, (5) Then the true enthalpy of fusion UHact

) of measured specimens is obtained from

AH(act) = E x AH(meas), (6) where AH(meas) is the measured enthalpy of fusion for that specimen. For extension to other temperatures a correction factor, F, is obtained from the sapphire

results:

F = C p (lit)/C

p (obs). (7) The AH(act) from eq (6) is multiplied by the ratio of the F-factor at the tem- perature of interest to the F-factor at the reference temperature. The F-factor normally changes somewhat with temperature; for that reason an F-factor specific

to the temperature of interest is used.

B. Results and discussion

Results for the temperature calibration study are shown in table 13 for the initial heating only. Results for repeat meaurements are given in table 14. The results for initial runs show the calculated temperatures in line 1. As the pro- cedure calls for bracketing the temperature of interest, naphthalene and

di phenylacetic acid were used to determine the values for acetanilide, which has

an intermediate melting temperature. Then acetanilide and anisic acid were used

to bracket di phenyl acetic acid, etc. The raw data used in the calculations are shown in table 13. In all cases the results of this study for initial runs agree with the certificate values. Though the standard deviations are greater than

-21-
Table 13a. Transition temperatures (K) - acetanilide (initial run)

Substance

31 Specimen No. 32 33 Mean

34 35 Standard Deviation

Acetani 1 ide 387.357 387.467 387.466 387.602 386.880 387.354 0.2 79 Naphthalene* 353.51 353.51 353.41 353.85 353.81 353.62 0.198

Di phenyl acetic Acid* 419.89 419.99 420.07 419.79 418.37 419.62 0.708 Acetanilide* 387.03 387.19 387.18 387.39 385.95 386.95 0.572 experimental transition temperature: 387.35 + 0.28 certificate transition temperature: 387.51 +0.05 [11]

Table 13b. Transition temperatures (K) - di phenyl acetic acid (initial run)

Substance

21 Specimen No.

22 23 24 Mean25 Standard Deviation

Di phenyl aceti c Acid 420.156 420.106 420.050 420.383 420.394 420.218 0.160 Acetanilide* 387.19 387.39 385.95 387.03 387. 18 386.95 0.572 Anisic Acid* 456.30 455.76 454.48 455.79 455.98 455.66 0.695

Di phenyl acetic Acid* 419.99 419. 79 418.37 419.89 420.07 419.62 0. 708 experimental transition temperature: 420.22 + 0.16 certificate transition temperature: 420.41 + 0.05 [11]

Table 13c. Transition temperatures (K) - anisic acid (initial run)

Substance

11 Specimen No.12 13 14 Mean15 Standard Deviation

Anisic Acid 456.644 456.092 455.694 456. 552 455.910 456. 180 0.409

Di phenyl acetic Acid* 419.99 419.89 419. 79 420.07 418.37 419.62 0.708 2-chloroanthraquinone* 482.36 482.51 483.24 481.91 481.68 482.34 0.604 Anisic Acid* 456.30 455. 79 455. 76 455.98 454.48 455.66 0.695

experimental transition temperature: 456.18 + 0.41 certificate transition temperature: 456.45 + 0.20 [11]

Uncorrected data from which corrected values were obtained utilizing the procedure out- lined in the text.

-22-
Table 14a. Transition temperatures (K) - acetanilide (repeat runs)

Run No. Specimen No. Mean Standard

31 32 33 34 35 Deviation

2 386.530 387.394 387.510 386.935 387.320 387.138 0.402

3 387.125 387. 723 387.211 387.988 387.882 387.586 0.394

4 387.085 387.342 387.231 387. 756 387.895 38 7.462 0.348

Grand Mean (20) Standard Deviation 387.385 0.370

Table 14b. Transition temperatures (K) - di phenyl acetic acid (repeat runs)

Run No. Specimen No. Mean Standard

21 22 23 24 25 Deviation

2 420.159 420.162 421.157 420.168 421.104 420.550 0.530

3 419.746 419.905 420.334 419.781 420.464 420.046 0.331

4 419.768 420.409 420.323 420.274 419.677 420.090 0.341

Grand Mean (20) Standard Deviation 420.226 0.391

Table 14c. Transition temperatures (K) - anisic acid (repeat runs)

Run No. Specimen No. Mean Standard

11 12 13 14 15 Deviation

2 456.810 456.331 455. 777 457.088 455.853 456.372 0.577

3 456. 575 456.697 456.383 456.826 457.139 456. 724 0.284

4 456.666 456.425 456.663 457.004 456. 774 456. 706 0.210

Grand Mean (20) Standard Deviation 456.495 0.433

-23-
those shown on the certificate, they are in line with those obtained in the indium study. The calculated values for repeat runs are shown in table 14. The results, shown in table 13, indicate that the ASTM two-point calibration

procedure can be used to establish suitable temperature calibration standards for d.s.c. They also indicate that the substances used in this study are useful cal- ibrants.

The results for the enthalpy measurements are shown in table 15. Columns 1-

5 refer to the replicate specimens. Rows 1-4 contain the data for the initial and three subsequent runs. The columns under full correction refer to the ASTM method using the results for sapphire in addition to those for indium, as de- scribed earlier in the paper. The columns headed fusion correction refer to the more commonly used method of correcting enthalpy by a factor obtained from an ex- perimental indium scan compared to its accepted value without any extension to other temperatures. Though the full correction is recommended by ASTM, results for the fusion only method are listed both because this method represents the most widely used method of making corrections and because a comparison of the two methods is desirable.

The enthalpies obtained with the full correction differ significantly from those with only the indium fusion correction for naphthalene, acetanilide and 2- chl oroanthraqui none . The results using only the indium correction generally

agree with literature values within experimental error; results using the full correction do not. Attempts are being made to resolve this difficulty through

communication with ASTM Committee E-37 (Thermal Methods) and by continued in- vestigation in this laboratory. Another concern in the study of these materials was their stability: Is it possible to reuse a specimen for repeated calibrations? The shape of the scans obtained with the five test materials sometimes varied with repeated use.

-24-
O **

ld cm r-» O

oo lo oo

>=i- r-- cr> cm

lo o

CO LO oo lo

LD O 00 LO CO LO OO MCOOOl

i—i r— oo o

00 LO LO 0O

in (ji ro *

P""- OO CNJ i—

LO LO 00

LO LO LO LO

Ol O LO OO

LO t-t LO 00 LO o

o o r-i oo

OO i~H O"* i—

LO i—I C\J o

O LO <T> CM CM LO LO LO CM CM OO M LO

cn o oo oo

r-~. LO lo oo

r- oo iNJ cfi .—I r-l r-l O

CTi CT» Ol CTi

LO OO LO LO

vf ro (\J lo

CM 00 LO o

LO LO 00 CXl CM ^J- CM 0O

cm r- oo

Ol CM O OO O LO 0O

rH LO CM CM 0O LO CO 0O LO O O CT> LO 00 ^t"

CXt i—l 0O 0O O LO o ^j- CM LO LO i—

,-1 C r-l r-l O .—I r-l r-l

LO LO LO LO

LO LC LO LO

o-i lo oo cri LO LC LO LO O CT^ LO 0O

cm oo cn o

LO LO CM Ol

00 ^1" r— o

25-
Examples of original and subsequent fusion scans for the test materials are shown

in figures 2-6. Anisic acid was remarkable for stability. 2 Though the en- thalpy of many of the substances does not differ significantly in repeat runs from that of the initial runs the shapes of the curves were often distorted. The automated program could not deal properly with temperature onset for these dis- torted curves. This fault is not in the procedure itself but in the logic of the commercial program used. In such instances, the onset temperature was satisfactorily evaluated manually. As far as use as standards is concerned, the deterioration of a material is not a problem. In instances in which such deterioration

takes place, it would be necessary to stipulate that fresh specimens be prepared

when needed. Table 16 summarizes the results obtained in the calibration study and gives

available literature values for comparison.

C. Summary

The temperature and enthalpy of transition certified for fusion standards

can be improved by more than an order of magnitude by use of the ASTM Recommended

Practice [7,8], The best results are obtained when like substances are used for the calibrations and when the temperature difference between calibrants is about

50 K. No blanket statement can be made about reusing standard specimens. If the curves are not distorted, the specimen may be used again; if the curves are mis- shapen, the specimen may not be reused.

2 Recent work with a new lot of anisic acid has shown that the acid contains im- purities which make it unsuitable for use as a standard. This fact reinforces the need to use certified materials as calibrants.

-26-
NARWTHALE>C FIRST RU*

TEMPERATURE OO

NAPHTHALENE FOURTH RUN,

TEMPERATURE <K) Figure 2. Initial and Final Runs for Naphthalene.

-27-
Figure 3. Initial and Final Runs for Acetanil ide. -28-
TEMPTRATUKE OO

TE>#TKATUKE OO

Figure 4. Initial and Final Runs for Diphenylacetic Acid,

-29-
anisic acid n*rr run

ANISIC ACID FOURTH RUN

J—Sum TLm 2a * * A. «T«

TEHPCTATURE OO

Figure 5. Initial and Final Runs for Anisic Acid.

-30-

Table 16. Summary of transition temperatures and enthalpies Substance

INITIAL RUN

ALL RUNS

LITERATURE

Naphthalene

Acetani 1 ide

Di phenyl acetic Acid Anisic Acid

2-Chl oroanthraqui none

Naphthal ene Acetani 1 ide

Di phenyl acetic Acid Anisic Acid

2-Chl oroanthraqui none

Naphthalene

Acetani 1 ide

Di phenyl acetic Acid Anisic Acid

2-Chl oroanthraqui none

Transition

Temperature (K) Enthal py of Transition (J/g)

387.35 + 0.28 420.22 + 0.16 456.18 + 0.41

149.35 + 0.85 163.65 + 1.26 148.67 + 1.32 195.49 + 1.11 148.15 + 0.76

387.38 + 0.37 420.23 + 0.39 456.50 + 0.43

149.01 + 1.18 163.40 + 1.343

148.16 + 1.28 195.31 + 1.53 146.81 + 1.20

353.37

387.51 420.41 456.14 482.20

148.6 160.2

147.3

207.91 135.35

NOTE: Naphthalene and 2-chl oroanthraqui none have no temperatures listed since they were the outer bracketing substances. *The enthalpies of transition given are those that have been corrected by the fusion correction only.

-32-
References

1. Callanan, J. E.; Sullivan, S. A. to be published.

2. Hudson, C. H., editor. NBS Standard Reference Materials Catalog 1984-5, Nat.

Bur. Stand. (U.S.) Spec. Publ . 260; 1984 February. 174 pp.

3. Garn, P. D.; Menis, P. Certificate for ICTA Certified Reference Materials

for Differential Analysis from 125-940 °C. 1971.

4. Brennan, W. P.; Gray, A. P. The cal or i metric precision and accuracy of a scanning calorimeter. Paper presented at the Pittsburgh Conference, March

1973. Reprint available from Perkin-Elmer Corporation, Instrument Division,

Norwalk, Connecticut, USA 06856 as Thermal Analysis Application Study 9.

5. Richardson, M. J.; Burrington, P. Thermal gradients in differential scanning

calorimetry. Journal of Therm. Anal. 6^: 345-354; 1974.

6. Mraw, S. C; Naas, D. F. The measurement of accurate heat capacities by differential scanning calorimetry. Comparison of results on pyrite (100-800 K) with literature values from precision adiabatic calorimetry. J. Chem. Ther- modynamics. JJj 567-584; 1979.

7. ASTM Standard Practice for temperature calibration of differential scanning

calorimeters and differential thermal analyzers E967-83. Annual Book of Standards. 14.02: 782-787; 1984.

8. ASTM Standard Practice for heat flow calibration of differential scanning

calorimeters E968-83. Annual Book of Standards. 14.02: 788-794; 1984.

9. McGlashan, M. L. Current trends in precise calorimetry. Thermochemica

Acta 72: 55-70; 1984.

10. Kafadar, K. Private communication.

11. NPL Certificate of measurement CRM No. M14-11. Set of ten melting point standards. National Physical Laboratory, Teddington, U.K.; 1980 November.

-33-
12. Pel la, E.; Nebuloni, M. Temperature measurements with a differential calo- rimeter. Journal of Therm. Anal. 3: 229-246; 1971.

13. Andon, R. J. L.; Connett, J. E.; Martin, J. F. The enthalpy of fusion of indium; certification of a sample for use as a CRM. NPL Report Chem. 101; 1979 July.

14. The international practical temperature scale of 1968 amended edition of 1975. Metrologia 12: 7-17; 1976.

15. McLaren, E. H. ; Murdoch, E. G. The freezing points of high purity metals as precision temperature standards (lead). Can. J. Phys. 38: 577; 1960.

16. Andon, R. J. L. ; Connett, J. E. Calibrants for thermal analysis. Measurement

of their enthalpies of fusion by adiabatic calorimetry. Thermochemica

Acta 42: 241-247; 1980.

-34-
Appendix

To judge the suitability of a DSC for the development of standards, it is necessary to identify and evaluate the various sources of experimental varia- bility in temperature and enthalpy measurements. In general, such variability

could arise from the DSC, from the procedures and laboratory conditions for working with the DSC, or from i nhomogenei ty among specimens of the reference

material. This appendix describes results of a study that was designed to iden- tify and quantify some of the sources of variation in the DSC procedure and the potential reference materials.

Temperature and enthalpy of transition were measured four times on each of five specimens from three forms of indium (granules, rod, foil). Each of the specimens was remounted in the calorimeter between repeat measurements. It should be noted that the latter protocol means that these data cannot provide

distinct estimates of remount variability and variation due to the instrument it- self. However, a measure of variability (inhomogeneity) among specimens for each form of indium can be obtained from the analysis.

A statistical analysis of variance shows that specimen-to-specimen variation

in enthalpy measurements is potentially significant for all three forms of in- dium. Evidence of inhomogeneity in melting points was found only for granular

i ndi urn.

A-1
Sample Data The data and summary statistics from this study are displayed in table 1 and table 2. Figures la-c and 2a-c illustrate the specimen-to-specimen (and

wi thin-specimen) variability that were observed in the data for temperature and enthalpy of transition, respectively. Specimen-to-specimen variation in temperature is clearly significant for granular indium, but no inhomogenei ty is apparent for the other forms of indium. For enthalpy measurements,

specimen-to-specimen variation is barely discernible for all three forms of

i ndi urn. Table 1. Fusion Temperature of Indium Within

Specimen

Form Specimen Temperature, K Std. Dev. Specimen

Mean

Granul ar 1 429.63 429.96 430.01 429.62 429.81

2 429.63 429.34 429.72 429.32 429.50

3 429.48 429.49 429.41 429.36 429.44

4 429.35 429.33 429.38 429.41 429.37

5 429.64 429.61 429.92 429.68 429. 71 Grand Mean 429.56

SD of Specimen Means 0.19

Rod 1 429.50 429.39 430.40 429.58 429.47

2 429.38 429.31 429.65 429.60 429.49

3 429.84 429.46 429.33 429.30 429.48

4 429. 78 429.37 429.75 429.67 429.64

5 429.56 429.52 429.36 429.43 429.47

0.21 0.20 0.06

0.04

0.14

Pooled 0.15

WithinSpecirnen SD 0.09 0.17

0.25

0.19 0.09 Grand Mean 429.51 Pooled 0.17

WithinSD of Specimen Means 0.08 Specimen

SD Foil 1 429. 71 429.60 429.74 429.67 429.68 0.06

2 429.53 429.72 429.83 429.45 429.63 0.17

3 429.53 429.50 429.48 429. 75 429.57 0.13

4 429.34 429.67 429.72 429.45 429.55 0.18

5 429.81 429. 74 429.25 429.54 429.59 0.25

Grand Mean 429.60 Pooled 0.17

WithinSD of Specimen Means 0.15 Specimen

SD

A-2
Table 2. Enthalpy of Fusion of Indium WithinForm Specimen Enthalpy , J/g

Specimen

Mean Specimen

Std. Dev, Granular 1 28.70 28.12 28.79 27.82 28.36 0.46

2 28.49 28.91 28. 62 28. 53 28.64 0. 19

3 29.00 28.83 28.95 28.87 28.91 0.08

4 28. 74 28.49 28.58 28.79 28. 65 0.14

5 28.79 28.70 28.45 28.28 28.56 0.23

Grand Mean 28. 62 Pool ed 0.26

WithinSD of Specimen Means 0.20 S pec i men

SD Rod 1 29.20 29.12 28.91 28.87 29.03 0.16

2 29.16 29.04 28.66 28.70 28.89 0.25

3 29.04 28.91 28.20 28.95 28. 78 0.39

4 28. 74 28.91 28.20 28.95 28. 70 0.35

5 28.45 28.41 28.28 28.45 28.40 0.08

Grand Mean 28. 76 Pooled 0.27

WithinSD of Specimen Means 0.24 Speci men

SD Foil 1 29.08 29.04 28.91 29.00 29.01 0.07

2 29.04 28.74 28.83 29.04 28.91 0.15

3 29.08 29.12 28.95 28.87 29.01 0.12

4 29.29 28.83 28.83 29.16 29.03 0.24

5 28. 79 28.62 28.87 28.66 28. 73 0.12

Grand Mean 28.94 Pooled 0.15

WithinSD of Specimen Means 0.12 Specimen

SD

Statistical Analysis

For measurements on a given form of indium, a useful model to describe both the within- and among-specimen variation can be represented as follows:

x

ij «» + 6i + V M

where

AGranular

430.2 r r

4292

2 3 4

Specimen

Figure la. Fusion temperature measurements for indium granules ( indicates specimen mean)

Rod

4302 I

430.0

g 429.8 !

& 429.6 I

429.4 h

4292

1 2 3 4 5 Specimen

Figure lb. Fusion temperature measurements for indium rod.

( indicates specimen mean)

A4
Fbil 4302 1

1 1

1 ,

+

- + - + +

+ ++

+

t

11 2 3 4 5 Specimen

Figure lc. Fusion temperature measurements for indium fc ( indicates specimen mean)

Granular

1 2 3 4 5 Specimen

Figure 2a. Enthalpy measurements for indium granules, ( indicates specimen mean)
Rod

29.50 i f i 1 2925 - +

+

+

-

29.00

+

+

- + + 28.75

+ a -

28.50

+ on pc

•• +

28.00

27.75 L_ I 1 2 3 Specimen

4 5

Figure 2b. Enthalpy measurements for indium rod. ( indicates specimen mean)

Foil

Speci

Figure 2c. Enthalpy measurements for indium foil, ( indicates specimen mean)
X.jj = measured temperature (enthalpy) for repeat run j on specimen i

y = "true" temperature (enthalpy) for the indium form

8^ = deviation of specimen i from the true temperature (enthalpy) «^ = "measurement" error for repeat run j on specimen i (includes effects

of remountiny, operating procedures, ambient conditions, as well as instrument error). For each fonn of indium, the index i runs from 1 to 5 = the number of specimens,

and j runs from 1 to 4 = the number of repeated measurements on each specimen.

The inhomogenei ty , <5^ , and measurement error, ^j, are assumed to have probability distributions that are approximately Gaussian with zero means and standard deviations a. and a, respectively. Thus, for the indium data, the model

0 represents variability in the data arising in two stages. First, all four meas- urements receive a common "among-specimen" deviation, Then each measure- ment gets its own wi thin-specimen error, *

-j j

The components of variance associated with differences between specimens

(a 2

) is a measure of inhomogenei ty in the reference material samples. The

5 wi thin-specimen variance (a 2

) comprises other relevant contributions to overall variability that arise because of the chosen experimental protocol.

A statistical analysis of variance corresponding to the model (1) was done (separately) on both temperature and enthalpy data for each form of indium. Es- timates of specimen-to-specimen variation and "measurement" error variation that were obtained from the analysis are shown in table 3. Significance levels for the hypothesis of no specimen-to-specimen variation are also given in table 3. The significance levels that were attained show a strong indication of variation

in melting temperatures between specimens of granular indium, but no evidence of significant variation for either rod or foil. However, all three forms of indium exhibited possibly inhomoyeneous enthalpies of transition among specimens.
Because the results suggest that the magnitude of among-specimen or wi thi n-specimen

variations may depend on the form of indium, a more general analysis (combining data from all forms) was not conducted.

Table 3, Estimated Specimen-to-Specimen and Within-Specimen Variation

Temperature Enthal py

Among Specimen- Significance

Repeats to-Specimen Level , Test

-2 .2 a = 0

Among Specimen- Significance

Repeats to-Specimen Level , Test

a a

Granul ar (0.148) 2 (0.171) 2 .0034 (0.256) 2 (0.153) 2 .0937 (0.270) 2 (0.193) 2 .0502 (0.148) 2 (0.097) 2 .0692

Rod (0.168) 2 0 .5419

Foil (0.170) 2 0 .7977

In order to evaluate the uncertainty of the grand mean of all measurements

on a given form, a proper estimate of the standard error is obtained by combining

both specimen-to-specimen variation (where applicable) and the experimental error variance. Statistical theory [1] gives the following formula for the true standard error of the grand mean of 20 form measurements under model (1):

The usual formula for the standard error of the mean, based on the simple (ungrouped) standard deviation of all 20 measurements, is not useful to estimate

this standard error. Estimates of average melting point and enthalpy of transition for indium

forms are given in table 4, along with standard errors that allow for specimen-to-specimen variation where appropriate. Simple standard deviations of the data were used to compute uncertainties of rod and foil melting points (based

on the results of the significance tests shown in table 3).

2 1/2

SE(X) = ( 20

A-8
Table 4. Estimated Fusion Temperatures, Enthalpies, and Standard Errors Mean Temperature

(K)

Standard

Error of Mean

(K)

Degrees of FreedomMean

Enthal py (J/g)

Standard

Error of Mean

(J/g)

Degrees of Freedom

Granul ar 429.57 0.08 4 28.62 0.09 4 Rod 429.51 0.04* 19 28.76 0.11 4 Foil 429.60 0.04* 19 28.94 0.06 4 *Computed assuming homogeneous specimens.

Reference

[1] Box, G. E. P., Hunter, W. G. , and Hunter, J. S. (1978). Statistics for Ex - perimenters , John Wiley, New York, pp. 571-583.

A-9
NBS-114A (REV. 2-8C) U.S. DEPT. OF COMM. 1. PUBLICATION OR 2. Performing Organ. Report No. 3. Publication Date BIBLIOGRAPHIC DATA REPORT NO. August 1985 SHEET (See instructions) NBS/SP-260/99

4. title and subtitle standard Reference Materials:

Feasibility Study for the Development of Standards Using Differential Scanning

Calorimetry

5. AUTHOR(S)

J. E. Callanan, S. A. Sullivan, and D . F. Vecchia

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions)

NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

7. Contract/Grant No.

8. Type of Report & Period Cover Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State, ZIP)

Same as item 6.

10. SUPPLEMENTARY NOTES Library of Congress Catalog Card No.: 85-600567

I | Document describes a computer program; SF-185, FlPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or literature survey, mention it here) The tremendous increase in the use of differential scanning calorimetry, coupled

with the decrease in the capability for conventional precision calorimetry, has created a need for more and better thermal standards for use with scanning calorimeters

and other thermal instruments currently available, such as thermomechanical analyzers.

The development of these standards by methods such as adiabatic or drop calorimetry is impractical because of the number and variety of standards required, the associated expense, and the lack of facilities and personnel to do the certification. A two-part

study was designed to evaluate the capability of a differential scanning calorimeter

for developing temperature and enthalpy of fusion standards. Part I evaluated the vari- ability of the differential scanning calorimeter (DSC) and factors which affected it; Part II applied American Society of Testing Materials (ASTM) procedures for the tempera- ture and heat flow calibration. The study shows that fusion standards can be developed

with a differential scanning calorimeter.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons) differential scanning calorimetry; enthalpy; fusion; pilot study; standards; temperature; thermal analysis

13. AVAILABILITY

EjXl Unlimited

[~~| For Official Distribution. Do Not Release to NTIS

[Xa| Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

fj^] Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

55

15. Pr

USCOMM-DC 6O43-P80
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Nonperiodicals

Monographs—Major contributions to the technical literature on various subjects related to the Bureau's scientific and technical activities. Handbooks—Recommended codes of engineering and industrial practice (including safety codes) developed in cooperation with interested industries, professional organizations, and regulatory bodies.

Special Publications—Include proceedings of conferences sponsored by NBS, NBS annual reports, and other

special publications appropriate to this grouping such as wall charts, pocket cards, and bibliographies. Applied Mathematics Series—Mathematical tables, manuals, and studies of special interest to physicists, engineers, chemists, biologists, mathematicians, computer programmers, and others engaged in scientific and

technical work.

National Standard Reference Data Series—Provides quantitative data on the physical and chemical properties of materials, compiled from the world's literature and critically evaluated. Developed under a worldwide pro- gram coordinated by NBS under the authority of the National Standard Data Act (Public Law 90-3%). NOTE: The Journal of Physical and Chemical Reference Data (JPCRD) is published quarterly for NBS by

the American Chemical Society (ACS) and the American Institute of Physics (AIP). Subscriptions, reprints, and supplements are available from ACS, 1155 Sixteenth St., NW, Washington, DC 20056.

Building Science Series—Disseminates technical information developed at the Bureau on building materials, components, systems, and whole structures. The series presents research results, test methods, and perfor- mance criteria related to the structural and environmental functions and the durability and safety

characteristics of building elements and systems. Technical Notes—Studies or reports which are complete in themselves but restrictive in their treatment of a

subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the subject

area. Often serve as a vehicle for final reports of work performed at NBS under the sponsorship of other government agencies. Voluntary Product Standards—Developed under procedures published by the Department of Commerce in Part 10, Title 15, of the Code of Federal Regulations. The standards establish nationally recognized re- quirements for products, and provide all concerned interests with a basis for common understanding of the

characteristics of the products. NBS administers this program as a supplement to the activities of the private

sector standardizing organizations. Consumer Information Series—Practical information, based on NBS research and experience, covering areas of interest to the consumer. Easily understandable language and illustrations provide useful background

knowledge for shopping in today's technological marketplace. Order the above NBS publications from: Superintendent of Documents, Government Printing Office, Washington, DC 20402. Order the following NBS publications—FIPS and NBSIR 's—from the National Technical Information Service, Springfield, VA 22161.

Federal Information Processing Standards Publications (FIPS PUB)—Publications in this series collectively constitute the Federal Information Processing Standards Register. The Register serves as the official source of

information in the Federal Government regarding standards issued by NBS pursuant to the Federal Property and Administrative Services Act of 1949 as amended, Public Law 89-306 (79 Stat. 1127), and as implemented

by Executive Order 1 1717 (38 FR 12315, dated May 11, 1973) and Part 6 of Title 15 CFR (Code of Federal

Regulations). NBS Interagency Reports (NBSIR)—A special series of interim or final reports on work performed by NBS

for outside sponsors (both government and non-government). In general, initial distribution is handled by the sponsor; public distribution is by the National Technical Information Service, Springfield, VA 22161, in paper copy or microfiche form.
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