NATL INST. OF STAND & TECH R.I.C.

A111DS D3tD75

REFERENCE

NBS SPECIAL PUBLICATION 260-70

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

Standard Reference Materials:

PREPARATION AND CHARACTERIZATION OF

AN IRON-CHROMIUM-NICKEL ALLOY

FOR MICROANALYSIS: SRM 479a
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards' was established by an act ol Congress on 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

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Standard Reference Materials:

PREPARATION AND CHARACTERIZATION OF

AN IRON-CHROMIUM-NICKEL ALLOY

FOR MICROANALYSIS: SRM 479a

R. B. Marinenko,

1 F. Biancaniello

2 L. DeRobertis,

3 P. A. Boyer

2 A. W. Ruff

2

1 Gas and Particulate Science Division Center for Analytical Chemistry

National Bureau of Standards Washington, D C 20234

2 Metallurgy Division Center for Materials Science National Bureau of Standards Washington, D C 20234

1 Statistical Engineering Division Center for Applied Mathematics

National Bureau of Standards Washington, D C 20234

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

NATIONALBUREAUOFSTANDARDS, Ernest Ambler, Director Issued May 1981
Library of Congress Catalog Card Number: 81-600043

National Bureau of Standards Special Publication 260-70

Nat. Bur. Stand. (U.S.), Spec. Publ. 260-70, 36 pages (May 1981) CODEN: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 1981

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

Price $2.50 (Add 25 percent for other than U.S. mailing)
PREFACE

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

National Bureau of Standards are wel 1 -character i zed 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.

This 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

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.

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 authors. 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

George A. Uriano, Chief

Office of Standard Reference Materials

i i i
OTHER NBS PUBLICATIONS IN THIS SERIES

Catalog of NBS Standard Reference Materials (1979-80 edition), R. W. Seward, ed., NBS

Spec. Publ. 260 (April 1979) $3.00* SN003-003-

02048-6

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. 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 Shouse, 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

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 Measure- ments 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). COM7 1-001 57**

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**

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 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: 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). COM7 1-50282 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). COM7 1-50563** 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**

V
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.) COM-72

50776** Wood, L. A., and Shouse, P. J., Standard

Reference Materials: Use of Standard LightSinsitive Paper for Calibrating Carbon Arcs Used in Testing Textiles for Colorfastness to Light, NBS Spec. Publ. 260^1 (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-O03-0 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. 260^7 (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. 260^18 (May 1974). 60 cents* SN003-O03-0 1278-5 Carpenter, B. S., and Reimer, G. M., Standard

Reference Materials: Calibrated Glass Standards for Fission Track Use, NBS Spec. Publ. 260^9 (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:

Electrolytic Iron, SRM's 734 and 797 from 4 to 1000 K, NBS Spec. Publ. 260-50 (June 1975). 1.00* SN003-003-0I425-7 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* SN003-003-

01464-8 Durst, R. A., Standard Reference Materials:

Standardization of pH Measurements, NBS

Spec. Publ. 260-53 (December 1975, Revised). $1.05* SN003-003-O1551-2

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 78 1

, From 273 to 2800 K, NBS Spec. Publ. 260-55 (September 1977). $2.20* SN003003-

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 (February 1978). $2.20* SN0O3-O03-0 18864

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

States Reference Materials, NBS Spec. Publ. 260-57 (February 1978). $2.20* SN003-003-

01883-0

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 (in press). 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* SN-003-

003-01975-5

i
Velapoldi, R. A., Paule, R. C, Schaffer, R., Velapoldi, R. A., Paule, R. C, Schaffer, R., Mandel, J., and Moody, J. R., Standard Refer- Mandel, J., Machlan, L. A., Garner, E. L., and

ence Materials: A Reference Method for the Rains, T. C, Standard Reference Materials: A

Determination of Sodium in Serum, NBS Spec. Reference Method for the Determination of

Publ. 260-60 (August 1978). $3.00* SN003-003 Lithium in Serum, NBS Spec. Publ. 260-69 (July) 01978-0 1980). $4.25* SN003-003-02214-4

Verdier, P. H., and Wagner. H. L., Standard Refer- Marinenko, R. B., Biancaniello, F., Boyer, P. A., ence Materials: The Characterization of Linear Ruff, A. W., DeRobertis, L., Standard Reference Polyethylene (SRM 1482, 1483, 1484), NBS Materials: Preparation and Characterization of Spec. Publ. 260-61 (December 1978). $1.70* an Iron-Chromium-Nickel Alloy for MicroSN003-003-02006-1 analysis, NBS Spec. Publ. 260-70 (in press). Soulen, R. J., and Dove, R. B., Standard Reference * Send order with remittance to Superintendent

Materials: Temperature Reference Standard of Documents, US Government Printing

for Use Below 0.5 K (SRM 768), NBS Spec. Office, Washington, DC 20402. Remittance

Publ. 260-62 (April 1979). $2.30* SN003-003- from foreign countries should include an

02047-8 additional one-fourth of the purchase price for Velapoldi, R. A., Paule, R. C, Schaffer, R., postage. Mandel, J., Machlan, L. A., and Gramlich, J. W., ** May be ordered from: National Technical Standard Reference Materials: A Reference Information Services (NTIS), Springfield, Method for the Determination of Potassium in Virginia 22151. Serum, NBS Spec. Publ. 260-63 (May 1979). $3.75* SN003-003-02068

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 for the Determination of Chloride in Serum, NBS Spec.

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

003-02136-9 Mavrodineanu, R. and Baldwin, Jr., 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

VI

1*
TABLE OF CONTENTS

PAGE

I. INTRODUCTION 2

II. ALLOY PREPARATION 2

III. CHEMICAL ANALYSIS 3

IV. PREPARATION FOR ELECTRON PROBE MICROANALYSIS . 6

V. HOMOGENEITY CHARACTERIZATION 7

VI. QUANTITATIVE ELECTRON PROBE MICROANALYSIS. . . 16

VII. CONCLUSIONS 19 VIII . REFERENCES 20 APPENDIX 2 2

viii
LIST OF TABLES

TABLE NO. PAGE

1. Comparison of Statistical Data from

Homogeneity Tests (wt. %) 11

2. Comparison of SRM 479 and SRM 479a 15

3. Electron Probe Microanalysis of SRM 479a. . 18

ix
LIST OF FIGURES

FIGURE NO. PAGE

la. Metal lographical ly polished surface of one disk specimen, unetched. M = 160X ... 4

lb. Metallographically polished surface of one disk specimen, unetched, a different

area. M = 640X 5

2a. Metallographically polished and etched

surface of one disk specimen showing

grain structure present. M = 160X ... 5

2b. Metallographically polished and etched

surface of one disk specimen showing

grain structure present, a different

area. M = 1 6 0 X 6

3. Periodic integrator homogeneity traces of

iron, chromium, and nickel simultaneously

recorded from NBS SRM 479a 9

x
ABSTRACT

An alloy of weight fraction 0.710 iron, 0.181 chromium,

and 0.109 nickel was characterized at the micrometer level

of spatial resolution by means of electron probe microanalysis. This alloy, designated SRM 479a, is of suitable

homogeneity for use as a standard in microanalyt ical techniques. There is no statistically significant variation in

composition within specimens or from specimen to specimen.

SRM 479a is supplied as a disk about 4.5 mm diameter by

0.8 mm thick.

Key Words: austenitic stainless steel; electron probe

microanalysis; Fe-Cr-Ni alloy; homogeneity

testing; Standard Reference Material.

1
I. INTRODUCTION

The National Bureau of Standards maintains a continuing

program to provide standards suitable for quantitative

microanalyt ical methods such as electron probe microanalysis

(EPMA) , spark source mass spectrometry, and laser probe

analysis. Several standard materials have already been

certified under this program [1-4]^. This report describes

the methods and results of homogeneity characterization of

an austenitic Fe-Cr-Ni alloy designated SRM 479a. This

alloy was produced to provide a reissue of a similar Fe-CrNi alloy, SRM 479 [4]. Suitable thermomechanical processing

treatments led to a material of acceptable homogeneity for

reference material use in microanalyt ical methods of analysis. The material preparation and the results of quantitative electron probe microanalysis of the constituent elements

are presented in this report.

II. ALLOY PREPARATION

The alloy was melted by the nonconsumable electrode

technique [5] in an arc furnace using appropriate amounts of

the raw material in the form of chips and small pieces. A reducing gas atmosphere consisting of 5 percent hydrogen in

argon was maintained within the furnace at a pressure of

about 0.3 atmospheres. This gas mixture was used to prevent

the formation of oxide inclusions during melting of the

alloy. A raw material charge of approximately 128 grams was melted using a non- consumable tungsten electrode. Each

of three hemispherical buttons was melted eight times, four

on each side, and then allowed to solidify in a depression

Figures in brackets indicate references at the end of this

paper

2
in the water-cooled, copper-base plate. Finally, the three

hemispherical buttons were placed together over another

depression in the base plate having a rectangular cross- section of about 15 cm x 1 cm x 1 cm, and consolidated by

melting into a single rod. The purities of the raw materials

used were: Ni - 99.99 percent, Cr - 99.99 percent, and Fe - 99.9 percent (Ferrovac E) . The target composition was 10.6

percent Ni, 18.8 percent Cr, and 70.6 percent Fe. The ingot was annealed for 1 hour at 1120°C within a sealed quartz tube containing helium at a pressure of 0.3

atmospheres. The ingot was then swaged to about 60 percent

reduction in diameter, sealed again in quartz, and homogenized for 5 days at 1120°C. Two subsequent swaging and

annealing steps produced the final round rod of 4.5 mm diameter x 32 cm long. At each step the rod ends were cropped and the surface etched deeply in a 20 percent nitric

acid plus 3 percent hydrofluoric acid solution. No lubrication was used during the mechanical processing. Each heat

treatment was concluded by quenching the sealed ingot into water. Five disks, 1 mm thick, were cut from the final rod

at each end and at the 1/4, 1/2, and 3/4 positions. These

disks were used for electron microprobe characterization of

the material.

III. CHEMICAL ANALYSIS

Chemical analysis was performed on representative

portions of the final rod. The samples were dissolved in

a mixture of hydrochloric and nitric acids. Sulfuric acid

was added after digestion and the samples fumed to remove nitric acid. The samples were then diluted. Nickel was determined spec tr ophotometr ical ly by a dimethylglyoxime

procedure. Chromium was determined by potent iometric titration of chromium with ferrous ammonium sulfate. The average

of eight measurements for nickel content was 0.109, with a

3
standard deviation of 0.0012 weight fraction. The average

of eight measurements for chromium content was 0.181, with

a standard deviation of 0.001 weight fraction. The amount

of iron by difference was 0.710 weight fraction.

SRM 479a is issued as a disk, approximately 0.8 mm thick

x 4.5 mm diameter, in the as-cut condition after diamond

blade slicing. The typical micros true ture found on metal

lographical ly polished and also etched 5 transverse surfaces

is shown in figures 1 and 2. The as-polished surfaces

(figure 1) indicate the appearance of the specimens as they

might be used for electron probe microanalyses. Some small

second phase particles were found near the outer edge of the

specimen disks studied. Figure 2 shows an example of an etched surface, indicating the grain size present. Some

small pits and voids that were not completely removed in the

processing treatments can be seen. Inclusions were rarely

detected in the central portions of the specimens examined.

Figure la. Metallographically polished

surface of one disk specimen,

unetched. M = 160X.

5 20mL HC1; 20 mL glycerine; 5 mL HNO _

; swab for 1 minute at 23°C.

4
Figure lb. Metallographically polished

surface of one disk specimen,

unetched, a different area. M = 640X.

Figure 2a. Metallographically polished

and etched surface of one disk specimen showing grain

structure present. M = 160X.

5
Figure 2b. Metallographically polished

and etched surface of one disk specimen showing grain

structure present, a different area. M = 160X.

IV. PREPARATION FOR ELECTRON PROBE MICROANALYSIS

This material was prepared for EPMA by grinding the

five disk specimens in one metallographic mount on waterlubricated SiC papers in the usual progression of 80, 220,

400, and 600 grit. Rough polishing was done on a cloth

impregnated with 6-ym diamond particles; fine polishing was done with 1/4-ym diamond particles. The specimen was finished using a cloth impregnated with 0.05-ym A^O^. In order to avoid embedding abrasive particles from the polishing steps into the surface, it is recommended that two or more cycles of polishing and etching be carried out as the

final steps. Unetched specimens were carbon - coat ed and

analyzed with EPMA. Pure element standard specimens were subsequently placed in the same mount as the Fe-Cr-Ni speci- mens for quantitative EPMA.

6
V. HOMOGENEITY CHARACTERIZATION

The tests described below were designed to evaluate

specimen microhomogeneity , or composition fluctuations from

micrometer to micrometer within the specimen, and to evaluate macrohomogeneity , or composition differences between

specimens taken from different positions along the rod

length. Testing was done with an NBS electron microprobe at an excitation potential of 20 kV. The probe emergence angle

was 52.5°. A point beam (about 1-um diameter) was used.

Three wavelength spectrometers with LiF crystals and sealed

or flow proportional counters were used to detect the Ka x-rays of iron, nickel, and chromium. The specimen current

- 8 was about 4 x 10 A. The highest count rate observed was 25,000 counts per second for pure nickel. The shortest

counting period used in these experiments was 10s. For the

alloy, the total number of counts per 10s was about 25,000

for nickel, 25,000 for chromium, and 75,000 for iron.

Since the analysis of the first SRM 479, a new microhomogeneity testing procedure has been developed at NBS. This method was used to check the transverse microhomogeneity

of the five specimens. The new procedure, which is described

in much greater detail in a recent publication [6], uses a periodic integrator based entirely on digital operations.

With a stepping motor on the stage, the specimen is moved

automatically under the electron beam in steps of 1 to 10 micrometers. X-ray counts are accumulated at each point for

a preselected time period (usually 10 s) , and the total

number of counts are then shown on a fast strip chart recorder

as an analog signal which remains unchanged during the next

counting period. The signal can be digitally multiplied by

any appropriate factor or a bias can be applied to digitally

subtract any desired count rate from the signal display.

7
The resulting visual display of specimen homogeneity on the

micrometer scale can be quickly obtained. An example is shown in figure 3. This periodic integrator trace is typical of those

obtained for all five SRM 479a specimens. Each specimen

was moved in 5-ym steps under a 1-um (approximate diameter)

electron beam. Counting periods were 10 s. The three

elements were simultaneously analyzed with LiF crystal spectrometers. Double-headed arrows to the right of the traces

indicate the theoretical ±3-sigma limits about the average

number of counts per counting period, N, for the trace. Sigma, o, equal to /N, is an unbiased estimate of the

standard deviation, according to Poisson counting statistics.

The ±3-sigma region provides a 99.7 percent confidence

limit. Deviations outside this range indicate inhomogeneit ies

,

assuming that no serious instrumental fluctuations are present

.

To the left of the figure is a t ime - resolved trace made

with a stationary 20 x 20-ym scanning raster. If there are

no serious systematic instrumental errors associated with

the testing procedure, this signal should lie within the

±3-sigma limits, as in fact it does. Variations within the

±3-sigma limits are due only to the expected statistical

fluctuations. For a truly homogeneous specimen, assuming a concentration large enough to produce a signal above background level, the trace for the moving specimen should be

similar to that of the stationary specimen. This, in fact, occurs here.

To test the transverse microhomogeneity of each of the

five specimens, two traces such as these, normal to one another and crossing near the center of the specimen, were

prepared. Each trace was 500 to 600 urn in length. Initially

the traces were made with steps of 1-um intervals. No significant concentration fluctuations were observed at this

spatial resolution. In order to cover more of the specimen,

8
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subsequent traces were made with 5-ym steps. No significant

deviations beyond the ±3-sigma limits were observed in any

of the traces.

In addition to the visual traces, a statistical evaluation was made on another homogeneity trace of each specimen.

The same experimental parameters were used for these traces

except that data readings were taken twice on each point.

The equations used in the statistical evaluation are explained in the reference cited previously [6] . From the

duplicate samplings of each point, the statistical analysis

separates the components of the standard deviation. A "within" standard deviation, o^, represents the precision of

repetitive counting, i.e., the error due only to counting

statistics. A "between" standard deviation, , represents

the difference between points. A comparison of these two standard deviations in weight percent for the five samples

is in Table 1. In no case is significantly greater than

a^, therefore indicating that the total error is due more to the measurement error than to specimen inhomogene ity . These

conclusions, of course, are based on the assumption that

there are no systematic instrumental errors present. No evidence of this, such as instrument drift, etc., was observed

.

The expression of these errors in weight percent as they appear in Table 1 required the conversion of net counts

(background- corrected) to concentration. The conversion

can be determined without a calibration plot if there is a linear relationship between the net counts and concentration

which passes through the origin. This linear relationship

was, in fact, validated for the three elements, iron,

chromium, and nickel, in SRM 479a.

Five mounted polished cross - sect ions of NBS steels,

SRM's 442, 443, 444, 446, and 447, were randomly sampled with

a 20 x 20-ym scanning raster at a 20 kV excitation potential

_ o and a specimen current of 4 x 10 A. The large scanning

10
Table 1. Comparison of Statistical Data from

Homogeneity Tests (wt. %) Comparison with

Homogeneity Trace Random Sampling

^RS /aw

2+ V

I Ni . 07 . 07 . 09 .10 Cr . 13 0 .11 . 13 Fe . 27 . 06 .49 . 28

II Ni . 08 . 04 .10 . 09 Cr . 12 . 06 .15 .13

Fe . 23 . 19 .47 .30 III Ni . 08 0 . 07 . 08 Cr .10 . 07 .10 .12 Fe . 22 . 10 .26 . 24 IV Ni . 07 . 06 . 08 . 09 Cr . 12 . 07 . 11 . 14

Fe . 26 . 28 . 29 .38 V Ni . 07 . 01 . 08 . 07 Cr .13 . 05 . 11 . 14 Fe . 30 . 24 .28 . 38

raster was used because the microhomogene ity has not been

established in these SRM's.

The concentration range for nickel in the five SRM's is 9.4 to 13.3 weight percent, and for chromium it is 16.1 to 23.7 weight percent. The iron concentrations range from

61.8 to 70.5 weight percent. This was slightly below the

certified composition of 71.0 weight percent for SRM 479a,

but no sudden changes from linearity would be expected at slightly higher concentrations. In all plots of net counts

vs. concentration the line fell at or near the origin; small

deviations from the origin would probably contribute little

11
to error calculations as the change in slope would not be

large. All subsequent error calculations were made with the

above assumptions.

A random sampling test was also done to evaluate

specimen microhomogene i ty . Fifty randomly selected points were sampled once on each specimen, and x-ray counts were accumulated for 20 s on each point. The results of this

test are also listed in Table 1. One standard deviation,

a^g, calculated from the 50 points is expressed here in

weight percent. These values of a^g agree favorably with

the combined components of variance, ^cr^ 2 + a^ 2

. A macrohomogeneity test, designed to evaluate differences

between specimens, was done on all five samples. Two different

operators were used for three experiments. The specimens were analyzed in a different order in each experiment and

six random samplings were made twice on each specimen in

each experiment, giving a total of 12 random samplings per

specimen per experiment. Counting periods were 20 s. Three contributions to the errors found in these

2 experiments were estimated. These are a Q , the variance

2 between the different specimens, a R , the variance within

2 specimens on the micrometer scale, and , the variance of

a single measurement error. The estimated values of these

variance components in weight percent as determined from the

three experiments for all specimens are:

„

2

rr 2rr 2 a

S a B

g

E Iron 0.5863 0.0638 0.0335

Chromium 0.0311 0.0028 0.0070

Nickel 0.0147 0.0016 0.0025

2 The between specimen component, a Q , is almost 10 times

2 greater than the within specimen component, ; i.e., the

macrohomogeneity or homogeneity along the rod length is not

as good as the microhomogeneity of a single specimen.

12
During this work the test results consistently showed a lower total number of counts for all elements in one end

specimen, which suggests the presence of unanalyzed elements

such as carbon on oxygen. Since only the center portion of

the rod was to be used for the SRM issue, the results

obtained from this specimen were excluded from subsequent

data evaluations. The following variance components were

then obtained (in weight percent)

:

Excluding Sample 1

a. Iron Chromium

Nickel

0. 2231

0. 0265

0. 0061

0. 0671

0. 0034

0. 0006

0. 0335

0. 0071

0.0025

As expected, the most significant change from exclusion of

sample 1 has occurred in the between specimen component,

The components of variance can be combined for an estimate of one standard deviation (1-sigma) of a single

measurement, a D

. This is given by:

/a

P

' In weight percent 1-sigma for a Iron Chromium

Nickel

single determination is 0.57

0.19

0.10

Assuming similar experimental conditions to those used in

these homogeneity studies, the average of 16 randomly

chosen points on a single specimen should, with 99 percent

probability, lie within the uncertainty interval given by

±3ap-: Iron 71.0 ±1.47

Chromium 18.1 ±0.49

Nickel 10.9 ±0. 24 This uncertainty, ±3ap-, is calculated from the estimates of

the variance components according to the equation

13
g

s

2 a B2 a E

2

a-p n

s n

s nB nsnBnE The uncertainty estimates above for SRM 479a are some- what larger than the 99 percent confidence intervals reported

for SRM 479 [4]. The values (in weight percent) reported

for SRM 479 were iron ±0.80, chromium ±0.20, and nickel

±0.12. These values were calculated from a 1.5 percent

coefficient of variation determined from homogeneity tests

on five specimens of SRM 479.

The difference in the uncertainty intervals for the two SRM's is due to the absence of the between specimen component, a

s

, for SRM 479. The homogeneity tests on SRM 479 [4]

showed no obvious differences between specimens.

When the current homogeneity studies on SRM 479a were being done, only one specimen of SRM 479 was available for

observation. The periodic ratemeter traces indicated that

the one available specimen was slightly less homogeneous

than any single specimen of SRM 479a. If this is the case, there is a possibility that spec imen - to - spec imen differences

(along the rod length) that we now see in SRM 479a were undetected in SRM 479 because -of the greater heterogeneity

observed within each specimen.

Table 2 compares the two specimens. Using the 1.5

percent coefficient of variation assigned to the microhomogeneity of SRM 479, a within- spec imen variance term,

2 2 Og + 0^ , is calculated. The values of this term for all

elements are greater for SRM 479 than for SRM 479a. These

numbers again suggest that the microhomogeneity of a single

specimen of SRM 479a is better than for SRM 479. The

standard deviation (1-sigma) of a single measurement is also

lower for the newer SRM in spite of the addition of the

large variance component associated with the differences

2 between specimens, . The 99 percent confidence intervals were calculated for both SRM's for two different experiments.

14
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c e 13 <D >

O SH o o o o

pa E II o\° »H (1) +1 +1 +1

t/) >H W Ol "-H *-> E-i 4-> u c oi c C o o ai

MEN u OO 00 o o

E ON t-~. O II ER

jn oo pa

a* </> <4-l u •• X rt o •> w <D C7> o m 0) 00 <+H DO to 6 X ii O rt , 00 vO o o o o N Bl C ODD

<D CO > o o o o o o

13 (1) > ^ 13

m ih id O MIh

to in aj

15
In experiment A, one specimen was randomly sampled 16 times,

while in experiment B, two random samplings were made on each of eight specimens. The second type of experiment

shows a marked improvement in dp, the standard deviation of

the average, and thus in the 99 percent confidence interval.

One implication of these results is that if the 99 percent

confidence intervals for SRM 479a in experiment A are not low enough, the only way to reduce these values is to increase the number of specimens of SRM 479a sampled.

VI. QUANTITATIVE ELECTRON PROBE MICROANALYSIS

The specimens from the 1/4, 1/2, and 3/4 positions as well as from the one acceptable end were quantitatively

analyzed with the electron microprobe. Two different NBS

electron microprobes were used as well as both wavelength

dispersive (WDS) and energy dispersive (EDS) spectrometers.

All analyses were conducted at an excitation potential of

2 0 kV.

WDS analyses were done on both instruments with three

LiF crystal spectrometers and proportional counters. A point beam (1 ym or less diameter) was used, and counting

periods were 40 s. The take-off angle for instrument 1 is 52.5° and for instrument 2 it is 40°. The specimen current

- 8 measured on an SRM 479a specimen was about 2 x 10 A. Standards were read before and after taking data from the

SRM 479a specimens. When needed, standards were read

frequently during the analyses to assure that there was minimal current drift (less than 1 percent) . Several (four

to six) randomly selected points were read on each standard

and SRM specimen.

Dead time corrections were made with the equation

N - _S^_

1 - N'T where N' is the observed count rate in counts per second, N

16

!
is the true count rate in counts per second, and t is the

dead time in seconds (See ref. [7] for a discussion of this

equation) . For instrument 1 the dead time is 3 ys and for

instrument 2 it is 1 ys. The highest count rate observed at the specimen current used was 14,000 counts/s for pure

nickel on instrument 1. An on-line correction procedure, FRAME [8], was used

to calculate the concentrations from the data of instrument

1. Another correction procedure, COR [9], was used for the

data from instrument 2. Although these programs are slightly

different, identical results were obtained when the same raw data was input for both. COR has an additional correction

for fluorescence due to the x-ray continuum, which in these

analyses did not significantly change the results.

EDS quantitative analyses were done on instrument 2.

- 9 The beam current was about 6 x 10 A and a 10 x 10-ym

scanning raster was used. The accumulation time was 200 s. Concentrations were calculated with the correction procedure

FRAME C [10]

.

The results of the quantitative analyses are in Table 3. For each experiment the instrument used and the technique

(WDS or EDS) are indicated. The first four experiments were

done with pure element standards. A specimen from the

original SRM 479 lot was used as the standard in the last

five experiments. A large discrepancy occurs in the values

obtained for chromium by the two different standardization

procedures. At an excitation potential of 20 kV, the matrix

correction procedure is apparently inadequate for chromium

in this alloy when using pure element standards. Similar

results were observed in the electron probe microanalysis of

SRM 479 [4] with pure element standards where at 20 kV the

calculated chromium concentration is considerably higher

(19.2 wtl) than the certified concentration (18.3 wt %)

.

More accurate results (better agreement with the certified

values) were obtained when using the SRM 479 specimen as a 17
Table 3. Electron Probe Microanalysis of SRM 479a.

Pure Element Standards Composition (weight percent)

Instrument Technique Fe Cr Ni

#1 WDS 70.6 19.7 10.9

#1 WDS 70.6 19.5 10.8

#2 WDS 70.8 19.2 10.5

#2 EDS 70.8 19.4 10.4

70.70(0.57) 19.45(0.28) 10.65(0.25)

SRM 479 Standard

Instrument Technique Fe Cr Ni

#1 WDS 69.0 18.6 11.0

#1 WDS 71.0 17.9 11.0

#2 WDS 70.0 18.4 10.6

#2 WDS 70.4 17.9 10.6

#2 EDS 69.9 18.7 10.6

70.06(0.90) 18.30(0.42) 10.76(0.23)

SRM 479 71. 0 18 . 3 10.

SRM 479a 71.0 18.1 10.9

aNickel and chromium were determined independently by wet chemical techniques and iron by difference.

standard where matrix correction procedures were minimal due

to the similarity between the standard and unknown specimens.

The errors cited are estimates of one standard deviation for

a single measurement, including the variation between

experiments as well as the variation due to macrohomogene i ty

,

microhomogeneity , and measurement error.

1 8
VII. CONCLUSIONS

The ternary alloy consisting of 0.710 iron, 0.181

chromium, and 0.109 nickel, as determined by chemical analysis, is suitable for use as a microanalyt ical standard.

This alloy, SRM 479a, has a chemical homogeneity expressed

as a coefficient of variation of not more than 1.0 percent

for each principal element present. The individual region

for which this coefficient of variation is valid is a sphere

of material approximately 1.5 ym in diameter. SRM 479

should be useful in any laboratory concerned with the quantitative microanalysis of stainless steels.

The authors acknowledge the chemical analysis measurements of B. I. Diamondstone and numerous helpful discussions

with R. W. Burke. The support of R. K. Kirby and R. Michaelis

in the Office of Standard Reference Materials is greatly

appreciated. Also, we thank M. C. Croarkin and H. H. Ku for

their helpful assistance in the handling of the statistical

results. Our thanks also to K. F. J. Heinrich who assisted

in the initial discussions on the homogeneity studies and the

electron probe quantitative microanalyses.

19
VIII. REFERENCES

[1] Michaelis, R. E . ; Yakowitz, H. ; Moore, G. A. Metallographic characterization of an NBS specti ometr ic

low-alloy steel standard. Nat. Bur. Stand. (U.S.) Misc.

Publ. 260-3; 1964 October. 17 p.

[2] Yakowitz, H. ; Michaelis, R. E.; Vieth, D. L. Homogeneitycharacterization of NBS spectrometr ic standards IV: preparation and microprobe characterization of W-20!Mo

alloy fabricated by powder metallurgical methods.

Advances in x-ray analysis. Vol. 12. New York, NY: Plenum Press; 1969. 418-438.

[3] Heinrich, K. F. J.; Myklebust, R. L. ; Rasberry, S. D. Preparation and evaluation of SRM's 481 and 482 goldsilver and gold-copper alloys for microanalysis. Nat.

Bur. Stand. (U.S.) Spec. Publ. 260-28; 1971 August. 89 p.

[4] Yakowitz, H. ; Ruff, A. W. Preparation and homogeneity

characterization of an austenitic iron- chromium-nickel

alloy. Nat. Bur. Stand. (U.S.) Spec. Publ. 260-43; 1972

November. 11 p.

[5] Nolson, S. J. Vacuum arc melting, consumable, non- consumable and skull, chapter 15 in Techniques of

metals research, Vol. 1. R. F. Bunshah, ed. New York:

Interscience Pubs.; 1968. 659-703.

[6] Marinenko, R. B-; Heinrich, K. F. J.; Ruegg, F. C. Microhomogeneity studies of NBS standard reference

materials, NBS research materials, and other related

samples. Nat. Bur. Stand. (U.S.) Spec. Publ. 260-65;

1979 September. 75 p.

[7] Heinrich, K. F. J.; Vieth, D. ; Yakowitz, H. Correction

for non-linearity of proportional counter systems in

electron probe x-ray microanalysis. Advances in x-ray

analysis. Vol. 9. New York, NY: Plenum Press; 1966.

208-220.
[8] Yakowitz, H. ; Myklebust, R. L. ; Heinrich, K. F. J. FRAME : An on-line correction procedure for quantitative electron probe microanalysis. Nat. Bur. Stand.

(U.S.) Tech. Note 796; 1973 October. 46 p.

[9] Henoc, J.; Heinrich, K. F. J.; Myklebust, R. L. A rigorous correction procedure for quantitative electron

probe microanalysis (COR 2). Nat. Bur. Stand. (U.S.)

Tech. Note 769; 1973 August. 127 p. [10] Myklebust, R. L. ; Fiori, C. E . ; Heinrich, K. F. J. FRAME C: a compact procedure for quantitative energydispersive electron probe x-ray analysis. Nat. Bur. Stand. (U.S.) Tech. Note 1106; 1979 September. 105 p.

21
APPENDIX

Let P be the true weight percent concentration of a particular element in the original alloy rod. Any single

(micrometer level) measurement P in weight percent taken at

a randomly selected point of a randomly selected specimen

will deviate from P

q because of variation between specimens

(macroheterogeneity) , variation within specimens (microheterogeneity) , and measurement error. Thus, the deviation

P - P may be viewed as a sum of "random effects":

o P=Pq +S+B+E,

where

,

P + S = true weight percent concentration in

the selected specimen;

P

Q

+ S + B = true (micrometer level) weight percent

concentration at the selected point of

the selected specimen; and

E = measurement error.

2 2 2 The "components of variance" , , are the

variances of the random effects S, B, E, respectively. The

2 of the measurement P is given by

2 2 2 2

CT P

= Q

S

+ aB+ a

E

' If n^ independent measurements are made at each of n^

randomly selected points of each of n^ randomly selected

specimens, and if P . . v denotes the k^*1 reolicated measurement at point j of specimen i, then the grand average

n

S nB

n

E „ E E E

P iik

has variance

n

F n

Bn

S i=l j=l k=l

P n^ iinii,, n^n^n.

Thus, the uncertainty in the average measurement P may be

2 2 2 estimated from estimates of , , and Gp . In

22
particular, an approximate 99 percent confidence interval

for the mean (micrometer level) concentration is

o 11/2

P ± 3

2 2 2 Estimates of , , were obtained as follows.

Let denote the k^*

1 count measured by the NBS electron

microprobe at point j of specimen i. And let D.., represent

1 J K the background count associated with the measured count

Y. ., . Assuming a linear relationship between the number of

1 J K counts above the background count and the (micrometer level)

weight percent concentration, Y. ., determines a weight

percent measurement P^j-^.= CY^^-^-D^^.^) / C where the conversion

factor C depends on experimental conditions (operating

voltage, counting time period, etc.).

Let

D = average background count, 6

y = — ij np ^ ljk

h k=l

Y. ., = average count at point j in specimen i

— 1 v — - Y. = — 2-» Y. . = average count in specimen i

n

s Y = ~ ^2 Y^ = grand average count,

S

i = l

6 Since the background count is low, it is treated as independent of which specimen, or which point within a specimen

is analyzed. Therefore, it is not read for every ijk. D is actually the average of five readings taken at the time of

the experiment.

23
E_ _ 2 (Y. - Y) = "between specimens sum of

1=1 squares",

n

S nB

= np ^ ^ ' " = "between points within

i = l j=l 1

-' specimens sum of squares".

Assuming Poisson variation for the background count and

for replicated counts at each point of each specimen, it follows that — — 2 2 (i) Y - D is an (unbiased) estimate of C dp ; — 2 2 (ii) M

2 /ns (ng-l) - D is an (unbiased) estimate of C (a

p +n

p a

] and

(iii) M

1 / (ng

- 1) - D is an (unbiased) estimate of

r 2 , 2^ 2^ 2. L (Op ^-p/^g n

B nE

a

S

* The estimated components of variance are thus taken to

(Y - D) /c 2

, (1)

be : 2 a

M

l M

) / "2

a ^

=

{ S^~~T ' n

g (n B

S

- Tj ] /

n

BnE

C

* (3)

where the conversion factor C is estimated by

C ="(T - D)/?

0 (4)

with P

q equal to the certified weight percent concentration

value determined by chemical analysis of the original alloy

rod.

It is essential to the above computations that the

conversion factor C remain constant throughout the experiment. Since current drift, etc., will induce changes in C, there are practical limitations on the number of measure- ments that may be taken in any one experiment. Hence, we

24
conducted three separate experiments (each with ng=4, ng=12,

ng=l) , and equations (l)-(4) were used to obtain three

estimates of each variance component; these were (weighted)

averaged to yield the final estimates quoted in the certificate.

25

it U.S. GOVERNMENT PRINTING OFFICE : 1981 O-340-997 (1685)
NBS-114A [rev. 2-8C) U.S. DEPT. O F COMM. 1. PUBLICATION OR 2. Performing Organ. Report No.l 3. Publication Date REPORT NO. BIBLIOGRAPHIC DATA

| May 1981 SHEET (See instructions) NBS SP 260-70

4. TITLE AND SUBTITLE Standard Reference Materials: Preparation and Characterization of an Iron-Chromium-Nickel Alloy for Microanalysis: SRM 479a

5. AUTHOR(S) R.B. Marinenko, F. Biancaniello, L. DeRobertis, P. A. Boyer, and A.W. Ruff

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions) 7. Contract/Grant No. NATIONAL BUREAU OF STANDARDS DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered WASHINGTON, D.C. 20234 Final

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

10. SUPPLEMENTARY NOTES Library of Congress Catalog Card Number: 81-600043

[~_~J Document describes a computer program; SF-185, FIPS 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)

An alloy of weight fraction 0.710 iron, 0.181 chromium and 0.109 nickel was characterized at the micrometer level of spatial resolution by means of electron

probe microanalysis. This alloy designated SRM 479a, is of suitable homogeneity

for use as a standard in microanalytical techniques. There is no statistically

significant variation in composition within specimens or from specimen to specimen. SRM 479a is supplied as a disk about 4.5 mm diameter by 0.8 mm thick.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons) austenitic stainless steel; electron probe microanalysis; Fe-Cr-Ni alloy;

homogeneity testing; Standard Reference Material.

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14. NO. OF PRINTED PAGES

36

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