National Bureau

of indards

A111D3 0 A 5 7 2

NBS SPECIAL PUBLICATION 260-28

Standard Reference Materials:

PREPARATION AND EVALUATION

OF SRM'S 481 AND 482

GOLD-SILVER AND GOLD-COPPER ALLOYS

FOR MICROANALYSIS
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards1 was established by an act of Congress March 3,

1 901 . The Bureau's overall goal is to strengthen and advance the Nation's science and

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NATIONAL BUREAU OF STANDARDS SEP 2 7 1371 UNITED STATES DEPARTMENT OF COMMERCE • Maurice H. Stans, Secretary NATIONAL BUREAU OF STANDARDS • Lewis M. Branscomb, Director mi ^ct,

a t ioo

Ml / Standard Reference Materials:

Preparation and Evaluation of SRM's 481 and 482

Gold-Silver and Gold-Copper Alloys for Microanalysis

Kurt F. J. Heinrich, Robert L. Myklebust,

Stanley D. Rasberry,

Analytical Chemistry Division and

Robert E. Michaelis

Office of Standard Reference Materials

Institute for Materials Research

National Bureau of Standards Washington, D.C. 20234

National Bureau of Standards Special Publication 260-28

too

Nat. Bur. Stand. U.S. , Spec. Publ. 260.28, pages (August 1971) CODEN: XNBSA

Issued August 1971

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. C13.10:260-28.) Price $1.00

Stock Number 0303-0899
Library of Congress Catalog Card Number: 75-176237
PREFACE

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

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

system to assure compatibility of measurement in the nation."

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

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

j United States and throughout the world. In many industries

:

| traceability of their quality control process to the national

' measurement system is carried out through the mechanism and

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

II know the details of the measurements made at NBS in arriving

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

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

:l N BS Special Publication - 260 Series is reserved for this

purpose

.

This 260 Series is dedicated to the dissemination of

information on all phases of the preparation, measurement,

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

or desirable, in scientific journal articles. This enables

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

and to learn details of techniques and methods utilized for

work entailing the greatest care and accuracy. It is also

hoped that these papers will provide sufficient additional

information not found on the certificate so that new applications in diverse fields not foreseen at the time the SRM

was originally issued will be sought and found.

iii
Inquiries concerning the technical content of this

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

concerned with the availability, delivery price , and so forth will receive prompt attention from:

Office of Standard Reference Materials

National Bureau of Standards

Washington, D. C. 2023^

J. Paul Cali, Chief

Office of Standard Reference Materials
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vii
I TABLE OF CONTENTS

PAGE

Preface iii

1. INTRODUCTION 2 A. Requirements for Standard Reference

Materials 2 B. Choice of Systems 3 C. Units for Composition 6

2. PREPARATION OF THE STANDARD REFERENCE

MATERIALS 7

3. CHEMICAL ANALYSIS OF BULK COMPOSITION 11

4. RESULTS OF HOMOGENEITY STUDIES 14

5. ANALYTICAL MEASUREMENTS WITH THE ELECTRON PROBE

ON SRM'S 481 AND 482 22

A. General Observations 22

1. Background Correction 23

2. Consistency Test on Experimental

Intensity Ratios 24

B. Data Obtained 30

C. Interpretation of Experimental Data .... 34

6. ACKNOWLEDGMENTS 37

7. LIST OF REFERENCES 38 APPENDIX 1: RESULTS OF ANALYTICAL MEASUREMENTS ... ^0

APPENDIX 2: CERTIFICATES OF ANALYSIS FOR SRM'S 481 AND 482

viii
PAGE

1. SRM 481 Gold-Silver Wires for Microprobe

Analysis 6l

2. SRM 482 Gold-Copper Wires for Microprobe

Analysis 64

APPENDIX 3: PRELIMINARY HOMOGENEITY TESTING .... 67

APPENDIX 4: AUTOMATED TECHNIQUES FOR HOMOGENEITY

ANALYSIS 70

A. Instrumental 70

B. Computation Technique 76

LIST OF FIGURES

FIGURE NO.

1. Measurements at 20 kV on copper-gold standard

reference materials 25

2. Analytical calibration curves for the copper

Ka line in gold-copper binaries at various

operating voltages 28

3. Same measurements as shown in Fig. 2 and

represented by plotting the ratio k/C on the ordinate and k on the abscissa .... 29

4. Experimental and theoretical intensity ratios

of copper Ka for a nominally Au60-Cu40

alloy 31

5. Experimental results on SRM 48l (Au-Ag) for

AuLa

x 41

6. Experimental results on SRM 48l (Au-Ag) for

AuMa 42

7. Experimental results on SRM 48l (Au-Ag) for

AgLa

x 43

8. Experimental results on SRM 48l (Au-Ag) for

AgL3

x ^

ix
PAGE

9a. Experimental results for three voltages on SRM 482 (Au-Cu) for AuLa^ 45 9b. Experimental results for all the voltages on SRM 482 (Au-Cu) for AuLc^ 46 10. Experimental results on SRM 482 (Au-Cu) for

AuL3

x 47 11. Experimental results on SRM 482 (Au-Cu) for

AuMa 48

12. Experimental results on SRM 482 (Au-Cu) for

CuKa 49 13. Experimental results on SRM 482 (Au-Cu) for

CuLa 50

14 . Block diagram of the matrix scanner 71

15- Front view of the matrix scanner 72 16. Sequence of automatic operations performed by

the matrix scanner 74

17. Statistics for . 6 Au in a . 6 Au - . 4 Ag

binary 82 18. Frequency distribution for the data presented

in Fig. 17 83 19. Relative topograph for the case given in

Fig. 17 84 20. Method of defining cluster size by counting

links 85 21. Pattern analysis for the relative topograph in

Fig. 19 86 22. Correlation graph for the case given in Fig.

17 88 23. Four possible outcomes for the correlation

graphs 89

x
LIST OF TABLES

PAGE

TABLE NO.

1. X-ray line wavelengths and absorption edge

wavelengths 5 2. Au-Ag Alloys SRM 48l - Big-beam determinations

of concentrations and standard deviations

on homogeneity test slices 16

3. Au-Cu Alloys SRM 482 - Big-beam determinations

of concentrations and standard deviations

on homogeneity test slices 17

4. Au-Ag Alloys - Standard deviations for

traverses 18

5. Au-Cu Alloys - Standard deviations for

traverses . 19

6. Au-Ag Alloys - Standard deviations for

rasters 20

7. Au-Cu Alloys - Standard deviations for

rasters 21

8. Comparison of background-determining methods

on Au-Cu alloys 26

9. Au-Ag, SRM 481 - Results for Au 51

10. Au-Ag, SRM 481 - Results for Ag 52

11. Au-Cu, SRM 482 - Results for Cu 53

12. Au-Cu, SRM 482 - Results for Au 54

13. Au-Ag, SRM 481 - Test calculations for Au . . 55 14. Au-Ag, SRM 481 - Test calculations for Ag . . 56

15. Au-Cu, SRM 482 _ Test calculations for Au . . 57

16. Au-Cu, SRM 482 _ Test calculations for Cu . . 58

17. Mass absorption coefficients used in the

preparation of Tables 13 to 16 59

18. Mean excitation potentials 59 xi

PREPARATION AND EVALUATION OF SRM'S 4.8 1 AND 482

GOLD-SILVER AND GOLD-COPPER ALLOYS FOR MICROANALYSIS

Kurt F. J. Heinrich, Robert L. Myklebust

and Stanley D. Rasberry

Analytical Chemistry Division

and

Robert E. Michaelis

Office of Standard Reference Materials

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

The reasoning behind the choice of the systems Au-Ag and

Au-Cu for SRM's, and their suggested uses are described. We also report on the preparations of the materials, their chemical analysis, the tests performed to ascertain macroscopic

and microscopic homogeneity, and on relative x-ray Intensity

measurements at various x-ray lines and voltages. A description of the instrumentation (matrix scanner), techniques, and

programs employed in the homogeneity studies, as well as tables

and graphs of the x-ray intensity measurements, are appended.

Key words: Alloys; corrections; electron probe; homogeneity;

matrix scanner; microanalysis; quantitative analysis; standard

reference materials; x-rav emission.

1
1. INTRODUCTION

A . Requirements for Standard Reference Materials

Although the foundations for a theoretical method of

calculating correction factors for quantitative electron

probe microanalysis were established in 1949 [1] } tests of

this method, performed a few years ago on specimens of known

composition, raised considerable question concerning capabilities of the electron probe microanaly zer as a quantitative

tool [2-4]. It became quite evident that various practical

techniques proposed for calculating the corrections [5-10] were in considerable disagreement and that in many cases

all proposed procedures failed to properly correct the experimental data obtained by experienced investigators. The resulting analytical errors frequently exceeded 10% relative.

A detailed analysis of these tests [3] suggested that the

following potential sources of error may be responsible for

these failures:

1. Some of the test specimens of presumably well known

composition may have been poorly characterized on a macroscopic scale or be microscopically inhomogeneous

.

2. Although the fundamentals of the generation of x-rays

by electron excitation are well known, there are uncertainties

In parameters and constants - such as the x-ray absorption

coefficients - which adversely affect the accuracy of the

method. The resulting uncertainties may be particularly

large if the instrument conditions have been chosen injudiciously [3, 11-14]

.

3. Lack of adequate computational facilities has frequently prompted the investigator to use simplified calculation procedures which may also introduce error.

Figures in brackets indicate references beginning on p . 38.

2
In order to improve the accuracy of the correction procedures for electron probe microanalysis, it is thus necessary

to obtain carefully prepared, microscopically homogeneous,

and chemically analyzed standard materials. The measurement

under carefully controlled conditions of x-ray emission

intensities from these standards, including all necessary

correction calculations [15], will permit an empirical

adjustment within the precision of the measurement of those

factors which are affected presently by uncertainty. Once

these factors have been established, the standard reference

• materials will enable the analyst to test the accuracy of

I his measurement technique by comparing the relative x-ray

intensities he obtains from such materials with those obtained

by other operators under carefully defined operating conditions .The Standard Reference Materials SRM 48l and 482 were

I selected, prepared, and tested in such a manner as to satisfy

2 the requirements indicated in Part 2 of this report . SRM 481

consists of a series of gold-silver alloys, and SRM 482 a series of gold-copper alloys, both in nominal steps of 20

weight percent and including the pure metals. We will describe

the reasons for choosing these particular alloys, their

preparation and their characterization, and we will report

the results of some x-ray measurements performed on them

(See Appendix 1).

B. Choice of Systems

SRM's 481 and 482 contain the elements of atomic numbers

29, 47, and 79, and therefore represent a good cross-section

through the range of higher atomic numbers. For copper,

An additional material of this type, SRM 480, which has a nominal composition of W80-Mo20 has been issued. It is described in NBS publication 260-16.
(atomic number 29), the mean excitation potential is relatively

well known; for this reason, it was selected as a starting

point for the empirical determination of mean excitation

potential by Duncumb [16]. The x-ray lines observable within

the typical range of electron probe spectrometers are the Cu K and L lines, the Ag L lines, and the Au L and M lines. Hence,

all three x-ray series are covered, the observable lines cover

a considerable wavelength range, and, for two of the elements,

more than one series can be observed (See Table 1)

.

All measurements are affected by significant atomic

number effects (stopping power and backseat ter ) . The Cu L,

Ag L, and Au M lines are also subject to strong absorption,

particularly at high operating voltages. Fluorescence due

to the continuum is significant for the intensity of the

Cu K and Au L emissions. The Cu K emission is also enhanced

by fluorescence due to the Au L lines.

The choice of these alloy systems was strongly influenced

by the fact that very accurate methods for the elemental

analysis of such alloys are available. Hence, the macroscopic composition of the standard reference materials can

be determined within an insignificantly small margin of error. Furthermore, the alloys, as well as the end members, are good conductors of heat and electricity, and can be polished

to satisfactory flatness without much difficulty. The elements of both binary systems are miscible in all proportions

and the alloys can be prepared with high homogeneity, as shown

in the tests to be described later.

Because of the high homogeneity and well-determined

composition, the standards should also be useful for other

methods of microanalysis, including laser probe analysis,

optical emission spectrometry, and spark source mass spectrometry .

4
Table 1. X-ray line wavelengths

and absorption edge wavelengths

Edge

AuL. AuL

AuLIIIII

CuK

AuM- AuM

AuM

AuM

AuM,

CuL- CuL

CuL

II

III

IV

IIIII

Au-Cu System

Line

AuL3- AuLa:

CuKa.

AuMa.

CuLa. AuN.

A (A) d

0 .86376

0 .90259

1.0400

1.08353

1. 27640

1.38059

1.54056

3.616

3.936

4 .518

5.374

5.584

5-84

11.27

13 . 014

13.288

13.336

16.27

Au-Ag System

AuL. AuL

AuLIIIII AgL

AgL

II AuM

^ AgLIII AuM

AuM

AuM

AuM.

IIIII

IV AuNj

AgMj

AuLa

AgL$-

AgLaAuMa0.86376

0 . 90259

1. 0400

1.27640

3.2564

3.5164

3.616

3.6999

3.93473

3.936

4 . 15443

4.518

5.374

5 .584

5.84

16.27^

17.24 b Extracted from "X-Ray Wavelengths," J. A. Bearden, U. A.E.C. Report NYO-IO586 (1964).

b Extracted from "The Physics of X-rays," M. A. Blokhin

AEC-tr-4502 (1961).

5
C . Units for Composition

In this report, composition is expressed in mass fractions. This unit is widely used by microprobe analysts in

analogy to k, the x-ray intensity ratio, which is also a fraction. Weight percents are retained in designating the

alloys (e.g., Au20-Cu80) and in the reproduction of the

certificates in Appendix 2.

6
2. PREPARATION OP THE STANDARD REFERENCE MATERIALS

In addition to the Au-Ag and Au-Cu systems described

in this report, several other systems were initially considered. These included Ag-Cu, Au-Al, Al-Ag, and Al-Cu, all

of which contain two-phase regions when prepared under equilibrium conditions. Two alternatives are available for the

preparation of such alloys; first, they could be solidified

in a non-equilibrium condition which would yield an apparent

single-phase. A possible technique for doing this is "splat

cooling" of molten drops [17]. Secondly, they could be produced as two-phase alloys, either from the melt or by powder

metallurgy, with identification and characterization of one

or both phases to be certified. This alternative has a major

technical difficulty in obtaining reliable chemical analyses

of the separate phases. We selected the simpler, single-phase

Au-Ag and Au-Cu binaries to be studied first.

That criterion established for acceptable homogeneity was that maximum variations in composition on both the macro- and

micro-scale should not exceed a range of 0.01 (mass-fraction).

Preliminary testing at NBS was carried out on the macro-scale

by residual resistivity ratios (R^^/R^), and on the macroand micro-scale by electron probe microanalysis . The pure metals and the four intermediate binary alloys

(nominal steps of 0.2) that comprise both the Au-Ag and the

Au-Cu system were prepared at Cominco American, Incorporated,

Spokane, Washington. Approximately 45 0 g (1 lb)

Electronic characterization was performed at NBS (Boulder, Col.)

by R. L. Powell, J. G. Hust, and R. L . Rutter. An introductory

treatment of electrical resistivity of metals is given by

Charles Kittel in Introduction to Solid State Physics , 3 rd Ed.,

John Wiley and Sons, New York, p. 218 (1966).

I Electron probe characterization was performed at NBS (Washington, D. C.) by K. P. J. Heinrich, M. A. Giles, and D. L. Vieth.

7
lots were made for each final wire using "6-9' s grade"

(nominal 99-9999$ purity) starting materials. Melting, casting,

and fabrication techniques were designed to ensure maximum

homogeneity and minimum contamination.

Weighed portions of the starting materials were melted

and cast into a single ingot, 25 mm (1 in.) in diameter, in

a high-purity graphite mold. Following surface preparation

of the ingot, numerous swaging and drawing operations were employed to produce wire 0.25 mm (.01 in.) in diameter. This

wire was spooled, bagged and shipped to NBS. To achieve

clean wire surfaces, the wire was drawn without lubricant.

A final etch (and frequently intermediate acid cleaning) was also employed.

The first wire for preliminary homogeneity testing was the Au20-Ag80 alloy. Several cross-sections were examined

by electron probe microanalysis and revealed the following:

(1) each specimen exhibited an outer layer approximately

30-um thick having a concentration of gold at least two-fold

greater than that found at the center of the wire; and (2) at the center of the wire, the mass fraction of gold differed

by more than 0.02 at points within 15 ym of each other. The

material was not suitable as a standard for microprobe analysis.

Preliminary testing continued on the three remaining

alloys in the Au-Ag systems with the following results:

(1) None of the three exhibited the Au-enriched outer layer

.

(2) The Au40-Ag60 alloy was unsatisfactory, in terms

of homogeneity over the cross-section, the Au60-Ag40 was marginal, but the Au80-Ag20 was entirely satisfactory.

(3) Electronic characterization for macro-homogeneity

agreed closely with the microprobe findings in that the

Au80-Ag20 was shown homogeneous to within 0.002; the Au40-Ag60

was found to be ten times less homogeneous.
The Au-enriched outer layer of the Au20-Ag80 was

j attributed to the preferential removal of Ag in the final

(etching procedure and this material was returned to Cominco

American, Inc. for repreparat ion omitting the final etching,

j On retesting, no evidence of an enriched Au outer layer was observed

Meanwhile, experimentation was conducted to establish

a homogenization heat treatment^. Success was achieved

whereby all the wires were shown to be within 0.01 by microprobe evaluations, and within 0.004 by electronic characterization. The homogenization heat treatment was performed

on all but the Au80-Ag20 alloy by placing each lot (coiled

| on a quartz drum, about 0.3 m in diameter) in a vacuum furnace

I at 650° C for 8 hours, followed by slow cooling in vacuum. Preliminary homogeneity testing of the four alloys of

j the Au-Cu systems revealed no outer-layer problem, but again

I a homogenization heat treatment was necessary for two of the

alloys, Au20-Cu80 and Au40-Cu60. Tests on short length wires

indicated the best heat treatment to be 8 hours in a vacuum

furnace at 700° C, followed by slow cooling in vacuum. After

coiling one of the alloys on the quartz cylinder and performing

this heat treatment, it was observed that a flashing of copper

had been deposited on the quartz cylinder. Chemical determinations were made to check the possible copper deficiency,

but fortunately, no significant difference on the bulk sample

was observed. As a precautionary measure, however, the final

homogenization heat treatment was altered to two 8-hour

soakings at 480° C in a nitrogen atmosphere of 0.02 torr in the vacuum furnace. Each soaking was followed by slow cooling

in the furnace. Additionally, the Au-Cu wires were proven

satisfactory in terms of preliminary homogeneity.

'Accomplished by C. W. Gifford and G. E. Hicho (National

Bureau of Standards, Institute for Materials Research).
Assay results, residual resistivity ratio measurements

and preliminary mlcroprobe results are given in Appendix 3. Final homogeneity studies by electron probe microanalysis

are reported in detail in Section 4.

10
3 . CHEMICAL ANALYSIS OF BULK COMPOSITION

Bulk analyses of the Standard Reference Materials SRM 48l

and 482 were performed by their manufacturer (Cominco American. Inc.), by the U.S. Bureau of the Mint, and by the

Analytical- Chemistry Division, National Bureau of Standards.

The results of the bulk analyses are as follows.

11
hO CD U H

cd cd > > o c o cd C o H tH S M O CD o 6< d . c a

•h 6 6 o o o

vo cm co oo o

eh cn in o

OA OA OA f— O H m in s oH O LT\ LP\ OO CO O O O O ^3- O O O C\J O CO VO -^T CM o i . CO o

CQ •H s -P

CJ co VO VO

cd 1 H o o < Ph 1 O o o CM

Cm 1 CO VO CM

CO

COcd S o LO. o OA

cd -p 1 o CO oa m

CD C < 1 o OA cr\ i>- -H 1 CM m LO. t

3 s 1 CQ

CD • 00 -P CM rH on 1 o r—1 o P Cm < 1 o O o CM O 1 CO VO -=r CM O o o

VO CO

bO bO bO <1 <1 <1 o o o o o

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4. RESULTS OF HOMOGENEITY STUDIES

Each alloy wire was Investigated using the electron probe

microanalyzer to determine homogeneity along the wire (longitudinal),, across the wire (transverse), and on microscopic

regions within the wire (micro-). Slices were taken at the two ends and at one to three intermediate positions along

each wire. Three transverse specimens from each of the slices were metallographically mounted and polished for the analyses.

Longitudinal homogeneity along individual wires was tested by using 25-ym diameter electron beam at two points

located in opposite quadrants of each specimen cross-section.

The average of the concentrations obtained from all the

slices of each alloy was assumed to be equal to the chemically

analyzed concentration. Table 2 lists the average composition

of each slice in the Au-Ag system together with its standard

deviation. A similar set of data for the Cu-Au system appears

in Table 3- Homogeneity along the wires was also tested by

measurement of the residual resistivity ratio. These measurements indicated that the variation (macroscopic) of composition along all standard wires was less than 0.001. Further

information on longitudinal homogeneity of the wires was obtained by fire assay determinations of Au at the extreme

ends of the alloy wire by the Bureau of the Mint; the data

also indicate that the extreme variation along the wires is

less than 0.001.

For transverse and micro-homogeneity testing, special

instrumentation, techniques, and computation procedures were developed. These are described in detail in Appendix 4. Transverse homogeneity was investigated at all slices along

the wire; for each slice, measurements were made along two diagonals at right angles. On each diagonal, determinations

were made at 25 points, 1 urn or less in diameter, starting

and ending at approximately 25 ym from the edge. The variation was calculated in terms of the standard variation for an 14
'individual determination for each traverse. The Au-Ag data

are presented in Table 4 and the Au-Cu data in Table 5- Micro-homogeneity was studied by performing measurements

in two-dimensional arrays of 10 x 10 points on each slice.

I The distance between centers of adjacent points was 3-5 ym.

! Two arrays were made in opposite quadrants of a specimen from

each slice. The observed standard deviations for individual

determinations are listed in Table 6 for the Au-Ag system and

in Table 7 for the Au-Cu system.

These studies, including those which were not performed

with the microprobe, indicate that both sets of SRM's are

well within the pre-established goal for homogeneity.

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5. ANALYTICAL MEASUREMENTS WITH THE ELECTRON PROBE

ON SRM'S 481 AND 482

Several operators performed measurements of x-ray intensity ratios using the standard reference materials mentioned

above. Further measurements are still in progress; therefore,

the results presented here should not be considered final.

However, they will serve to illustrate the information which

can be obtained from these standards and some of the difficulties which present themselves in the process.

A . General Observations

The standards, in the form of cleaned wires, were mounted

by press-fitting them into holes drilled into blocks of aluminum or brass. The assembly was then backed by epoxy resin

to hold the wires firmly in place, and the cross-sections at the surface of the mounting blocks were carefully polished,

finishing with 1/4- um diamond paste. Since no nonconductive

material appeared at the specimen surface, it was not necessary

to coat the specimens.

The high voltage power supplies used in these measurements were calibrated by observing the minimum nominal voltage

of excitation of selected lines. Therefore, the potential

difference between the filament and the negative side of the

bias resistor was eliminated as a source of error. The pulseheight analyzers of each channel were used in the discriminator

mode, and the amplification of the linear amplifiers was carefully adjusted so that the peak of the pulse-height distribution was five times the height of the discrimination

level. The dead time of each channel had been carefully

measured as described elsewhere [18]; dead time was about

3 ysec.

The size of the beam cross-section was enlarged to 3-5 ym

in order to reduce the effects of contamination, and each

measurement was performed at a site which had not been exposed

22
previously. The specimen remained in a fixed position during

the exposures.

Before initiating measurements, the filament was allowed

to emit for at least 30 minutes, in order to assure stability

of electron emission. The electron optics were realigned

before each set of measurements by readjusting the anode plate

to maximum target current.

The measurements were performed on scalers by accumulating

the number of pulses obtained from each specimen within a fixed time period. Within each set of measurements, each

alloy was measured at least twice. The end-member elements

were read at the beginning and the end of each set. (This, in

fact, defines the limits of a set of measurements.) If the

measurements on the pure elements emitting the line in

question differed by one percent or more, the series of

measurements was rejected. If the measurements of the binary

alloys differed among themselves by more than one percent

of the readings of the corresponding end member, more measurements were performed within the corresponding set of measurements . Wherever possible, several lines were measured in the

same operation. However, the beam Intensity was adjusted

in each case to limit the counting rates to a maximum of

15 3 000 counts/sec. When, under these conditions, another

set measured simultaneously showed excessive counting error, this set was rejected and rerun at a larger beam current.

1 . Background Correction

In most series, the background was assumed to be equal

to the measurement on the end member not containing the

emitting element. This practice is open to the objection

that the background intensity - which consists mainly of

the continuum contribution - increases with increasing atomic

number. However, if the background increases or decreases

23
proportionally to the variation of the line emission, the

resulting error cancels. Experimental measurements of background variation as a function of composition (Figure 1)

indicate that the background varies nearly linearly with

composition. Therefore, the resulting error should be small,

as long as the analytical calibration curve is close to linear.

Strong deviation from linearity occurs mainly in the case of

strong absorption corrections. These are observed only for

lines of long wavelength for which the line-to-background

ratio is fairly large (>100) . It can thus be expected that

the errors resulting from the proposed background correction

technique for binary alloys will be negligible. This proposition was tested for three cases by determining the background

in the proposed manner, as well as by actually measuring the

background intensity close to the observed line. The results

obtained (Table 8) indicate that the results of both procedures

are identical within the accuracy of the measurement.

The advantages accruing from the simplicity of this

background correction procedure are obvious. when it is

applied to soft x-ray lines, and when low concentrations are measured, it is important to avoid superficial contamination

of the background standard - such as smearing effects on a gold surface, particularly if the standards are mounted in

brass. Extension of this technique to systems other than

metal binaries will be described in a future publication.

2 . Consistency Test on Experimental Intensity Ratios

Since the purpose of the measurement of intensity ratios

(henceforth called k) is to test theoretical correction procedures, it would not be possible to test the accuracy of

the measurements used In calculating k by comparing the

experimental results with theoretical predictions. It can

be safely assumed, however, that for a given line and operating voltages, the k values within a binary system will

24
0 .20 .40 .60 .80 I WEIGHT FRACTION OF GOLD

Figure 1. Measurements at 20 kV on copper-gold standard

reference materials. The signal intensities

are on an arbitrary scale. Both target current

and continuous radiation (background at 2.29 *k) vary linearly with mass fraction.

25

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26
vary smoothly with the weight fraction of the measured element, C, converging to zero as C tends to zero, and to unity

as C tends to one. Hence, a plot of experimental k values

as a function of C (analytical calibration curve) must give

a smooth curve with the end points (0,0) and (1,1). However,

small deviations from smoothness are not easily apparent on such a plot. It is therefore preferable to use a simple

transformation, plotting the ratio k/C as a function of k,

(or the ratio C/k as a function of C). In such a plot, the

vertical scale (k/C) can be expanded to any desirable degree

so that small irregularities of the calibration curve become

more apparent (see Figure 2 and 3).

It is interesting to observe that the hyperbolic approximation of Ziebold and Ogilvie [8] postulates that the plots

of k/C vs. k and C/k vs. C yield straight lines. The proposed

plot is therefore also a test of this approximation.

Deviations from smoothness of the k/C plot indicate an error in either the measured k value or the assumed composition (C) . If the assumed composition is in error, a similar

deviation will result on all measurements of the element in

question in the standard, regardless of the line and operating

voltage used. Furthermore, in a binary alloy, the complementary element would exhibit a comparable deviation in the

opposite direction since the sum of C of both elements is

equal to unity. On the other hand, errors in individual

measurements will not produce similar correlations. An inspection of the curves obtained from the standard reference series

(Figures 5 to 13) indicates no such correlations. One must

conclude that any irregularities observed in the plots are results of measurement errors. One may not, however, conclude

that conversely a smooth k/C curve is proof of correct chemical

analysis, since systematic errors in the chemical analysis

could produce a smooth shift of the k/C curve.

27
Figure 2. Analytical calibration curves for the copper

Kot line in gold-copper binaries at various

operating voltages. Background-corrected

intensity ratios, k, are plotted vertically

and mass fractions of copper, C, horizontally.

28
Figure 3- The same measurements as shown in Figure 2 are represented by plotting the ratio k/C on the

ordinate, and k on the abscissa. The ordinate

scale can be expanded to any degree; therefore,

the scatter of experimental data is easier to observe than in Figure 2. The thin, almost

vertical lines connect points corresponding

to the same composition, which can be read on the horizontal scale, where k = C.

29
If the measurements of all alloys of a binary system

for a line and operating voltage were made in the same set or sets of measurements (as in our study), an error in standardization, or in the assumed operating voltage, could

smoothly shift the k/C curve. Such systematic errors are not very obvious on the k/C plots. However, it can also be safely

assumed that, above the minimum excitation potential, the

values of k must shift smoothly as a function of accelerating

voltage. A test for errors affecting a whole series of

measurements can thus be performed by plotting the value

of k (or of k/C) as a function of accelerating voltage for

each alloy. In the absence of measurement errors, a smooth

curve should be obtained. One may plot on the same graph

the k values predicted by various theoretical procedures; thus,

the accuracy of the procedures can also be tested (Figure 4).

Alternatively, one may plot the analytical error (i.e., the

difference between the assumed C and the value of C obtained

from the experimental k, by means of various theoretical

procedures). In absence of measurement errors, the obtained

curves should also be smooth.

B. Data Obtained

The x-ray intensity measurements presented in this section

consist of a preliminary set of data (obtained by operator 1)

and some complementary measurements (operator 2 and 3)- Since

all these measurements were exploratory, in many instances

their precision is inferior to that which we ultimately hope

to attain. Nevertheless, the data provide very interesting

information

.

The results are presented in the following form:

1. A table for each element and SRM set gives the mean intensity ratios, k, as well as estimates of the standard

deviation of a single measurement, where available (Tables

9 to 12, Appendix 1). The estimates were derived from the

30
31
observed range of k values [19]. To obtain an estimate of

the standard deviation of the mean value reported, the

estimates , s, should be divided by the square root of the

number of data points. Where only one data point was obtained, no value for s is reported.

2. A plot of k/C as a function of k is shown for each

SRM set and each measured x-ray line (Figures 5 to 13,

Appendix 1). This graph provides an estimator of precision,

particularly for single measurements.

3. A table for each SRM set and element compares the

experimentally obtained k values with theoretically predicted

values for a nominal concentration of 0.4 in the element

being investigated (Tables 13 to 16, Appendix 1). Besides

the lines measured, operating voltages, experimental k values

(k ), and their estimated standard deviation, s , these

ex 5 s ex 5 tables contain: a. the value of k calculated by the computer

program COR [20], with use of the values for the mean excitation potential, J, proposed by Berger and Seltzer [21] - this

value of k is called k„„: b. the difference k - k_,„_, „ c , COR exp C0R,B-S 5 called Ak ; c. the absorption function f(x) [15], for priex mary radiation, according to COR; d. the difference in k

obtained when the x-ray mass absorption coefficients recently

proposed by B. L. Bracewell and W. J. Veigele [22] are substituted for those published earlier by Heinrich [23] and

normally used in COR (Ak(u/p)) (See Table 17, Appendix 1);

e. the difference in k obtained when the J values of Duncumb

[l6 ] are substituted for those of Berger and Seltzer (Ak(J))

(See Table 18 , Appendix 1); f. the difference in k obtained

when the corrections for fluorescence by the continuum are omitted in COR (Ak(cont)); and g. the difference in k obtained

when the program MULTI 8 [24] is used rather than COR, with

the fluorescence due to continuous radiation being disregarded

in both programs (Ak(prog)).

32
The differences between k and k give an indication

ex UUri of the accuracy of theoretical correction procedures which

are widely used at present. The function f(x) and the value

of Ak(y/p ) indicate how sensitive the value of k is to changes

in the mass attenuation coefficients and in the analytical

form of the absorption correction. The values of Ak(J) are

a yardstick for sensitivity of the procedure to variations in

the model for stopping power. It is not implied that the two

sets of values of the mass attenuation coefficients and of J cover the range including the correct values, nor is any

preference between the sets implicit in the information which

is presented here.

The next column shows the variation of k caused by omitting the correction for continuous fluorescence. When this

difference Ak(cont) is small, the corresponding correction

is insignificant as a potential source of error. The difference Ak(prog) in the last column indicates how well the

results of MULTI 8 check with those of COR -with the continuum

fluorescence correction omitted. The main differences, besides

continuum fluorescence, are in the stopping power term, which

is numerically integrated in COR as a function of energy,

while MULTI 8 uses an approximative procedure developed by

H. Yakowitz [25], and in the treatment of fluorescence by

characteristic lines. In COR, a rigorous treatment of the

characteristic fluorescence is used to separately calculate

the effects of each major exciting line. In MULTI 8, instead,

the approximative procedure of Reed [26] is followed. Hence,

in absence of mistakes in the programs, Ak(prog) can be

expected to be negligibly small, except in the presence of

fluorescence due to characteristic lines, and at very low

overvoltages where the effects of electron deceleration are critical

33
C . Interpretation of Experimental Data

Standard Reference Materials Set 48l Au La^: In this system, the effects of absorption are negligible while those of the continuum and of the mean excitation potential are significant (-.005). No characteristic

fluorescence is present. Within the experimental scatter - which is fairly large - the k values obtained experimentally

check reasonably well with those calculated by COR (B-S).

Au Ma : Experimental data at operating voltages below

30 kV show excessive scatter. The form of the 5 kV curve suggests possible surface contamination on the standard. In spite of these limitations, it is obvious that the experimental

values deviate significantly from those obtained by calculation. At low voltages (5-20 kV), the stopping power calculation seems to fail. The discrepancy at high energies is

probably due to inaccuracy in the absorption correction; the

values obtained from the use of the Kaman mass absorption

coefficient tables fit reasonably in this case. Ag La^, Ag Lg-^: With the exception of the 5-kV measurement s7~^^eTr~vlilue

-s for Ag La^, and all values for Ag Lg^,

are highly self-consistent; statistical scatter, where measured,

is low.

For both lines, the absorption losses are high and the

absorption uncertainty is large, particularly at high voltages,

since the lines fall into the region between Au M absorption

edges. In particular, Ag L3^ is exceedingly close to the

edge Au M^ (See Table l). With either set of mass absorption

coefficients, the experimental k values are consistently low,

particularly at high operating voltages. This suggests an inaccuracy in the absorption correction model.

34
Standard Reference Material Set 482 Au La^: Measurements at 15 kV and at 40 kV are of low

accuracy. It would be quite difficult to obtain accurate

measurements at 15 kV, in view of the high critical excitation

potential of the line and the high background level. The

measurements in the center of the energy range check well

with the calculations by COR (B-S); values derived from the

J factor of Duncumb are slightly low. Au L3^: The experimental k values available to date are consistently higher than the calculated values. The reason

for this is not clear, particularly since the agreement is

fairly good for the Au La^ values. There is no fluorescence

by characteristic lines and the absorption losses are insignificant. The main effects to be considered are fluorescence

by the continuum and the atomic number effect (electron

deceleration and backscatter )

Au Ma : The experimental k values are quite selfconsistent. Comparison with computed values indicates a failure of the stopping power correction, observable by the discrepancies at low voltage. This is not surprising, since

there is a strong effect of the choice of expressions for

stopping power. At high energies, the absorption losses and,

hence, the corresponding uncertainty are high. The experimental

values decrease more rapidly than predicted by COR.

Cu Ka : The experimental k values are reasonably precise

except for extremely low (12 kV) and very high (40-48.5 kV)

energies. They check quite well with the values predicted

by COR. However, effects of fluorescence by both Au L lines

and by the continuum are significant in this system, and

introduce some uncertainty which precludes drawing more precise conclusions with respect to the accuracy of the atomic

number corrections.

35
Cu La : Experimental data are quite self-consistent

except below 10 kV where, apparently, contamination of the

specimens and the pure element caused severe errors. In view

of the large absorption losses, the experimental fit to the

results obtained from COR is surprisingly good. The values

for mass attenuation coefficients were, in this case, obtained

by extrapolation of the values used in COR. Fluorescent

excitation can be neglected, but the absorption uncertainty

is very large.

36
6 . ACKNOWLEDGMENTS

The thoughtful cooperation of T. Rice "and J. Frettingham

of Cominco American, Inc. and H. Hanson, Jr. of the Bureau

of the Mint has greatly aided the completion of this project.

Assistance from numerous members of the NBS staff has been

received in all phases of this work; we would especially

like to acknowledge the help of C. Fiori, M. Giles, K. Loraski,

B. Scribner, V. Stewart, D. Vieth, J. Baldwin, R. Durst,

C. Gifford, G. Hicho, J. Hust, B. Joiner, M. Meyerson, R. Paulson, R. Powell, and R. Rutter.

37
7. LIST OP REFERENCES

Castaing, R., Doctoral Thesis, U. Paris, 1951.

Thomas, P. M. , At. Energy Res. Estab. (Gt. Brit.)

Rept. 4593 (1964).

Heinrich, K. F. J., Adv. in X-ray Analysis 11_ (Plenum

Press, New York, 1968) p. 40. Poole, D. M. , in NBS Special Publ. 298 , 93 (1968).

Thomas, P. M. , Brit. J. Appl . Phys . l4_, 397 (1963).

Duncumb, P. and Shields, P. K., in The Electron Microprobe , T. D. McKinley, K. F. J. Heinrich, and D. B. Wittry, Eds. (J. Wiley and Sons, Inc., New York, 1966)

p. 284.

Belk, J. A., Birmingham C.A.T. Tech. Note, MET/26/1964

(1964).

Ziebold, T. 0. and Ogilvie, R. E., Anal. Chem. 35., 621 (1963).

Archard, G. D. and Mulvey, T., X-Ray Optics and X-Ray

Microanalysis (Academ. Press, New York, 1962) p. 393-

Theisen, R. , Quantitative Electron Microprobe Analysis

( Springer-Verlag , New York, 1965 )

•

Yakowitz, H. and Heinrich, K. F. J., Mikrochim. Acta

1968 , 182.

Heinrich, K. F. J. and Yakowitz, H. , Mikrochim. Acta

1968 , 905.

Heinrich, K. F. J. and Yakowitz, H. , Mikrochim. Acta

1970 , 123.

Heinrich, K. F. J. and Yakowitz, H., Proc. Vth Internat

.

Congress on X-ray Optics and Microanalysis, Tubingen,

1968, G. Mollenstedt and K. H. Gaukler, Eds. (SpringerVerlag, Berlin, 1969) p. 151.

Heinrich, K. F. J., NBS Tech. Note 521_ (1970 ). Duncumb, P. and Reed, S. J. B., in NBS Special Publ.

298, 133 (1968).

38
[17] Goldstein, J. I., Majeske, P. J., and Yakowitz, H. , Adv. In X-ray Analysis 10, 217 (1967).

[18] Helnrich, K. P. J., Vieth, D. a and Yakowitz, H. , Adv.

in X-ray Analysis 9_, (Plenum Press, New York, 1966)

p. 208.

[19] Natrella, M. G . , Experimental Statistics , NBS Handbook

91, 2-6 (1963).

[20] Scribner, B. F. , ed . , NBS Tech. Note 542_, 25 (1970).

[21] Berger, M. J. and Seltzer, S. R. , "Tables of Energy

Losses and Ranges of Electrons and Positrons," Natl.

Acad. Sci., Nat. Res. Council Publ. 1133 , 205 (1964).

[22] Bracewell, B. L. and Veigele, W. J., "Tables of X-ray

Mass Attenuation and Absorption Coefficients for 87

Elements at Selected Wavelengths," Report, Kaman

Sciences Corporation, Colorado Springs, Col. (1970).

[23] Helnrich, K. F. J., "X-ray Absorption Uncertainty," in

The Electron Microprobe (J. Wiley and Sons, Inc.,

N. Y. , 1966) p. 296.

[24] Available on request from the Spect rochemical Analysis

Section, NBS, Washington, D. C. 20234.

[25] This procedure, as yet unpublished, is a fit to the curve shown in Figure 5 of reference [13].

[26] Reed, S. J. B., Brit, J. Appl . Phys. 16_, 913 (1965).

[27] Scribner, B. F . , ed., NBS Tech. Note 422_, 34-35 (1968 ). [28] Scribner, B. F., ed., NBS Tech. Note 452 , 26-30 (1968).

[29] Yakowitz, H. and Helnrich, K. F. J., Metallography 1,

55 (1968).

39
APPENDIX 1 RESULTS OF ANALYTICAL MEASUREMENTS

40
Figure 5. Experimental results on SRM 48l (Au-Ag) for

AuLa^ . Bars in Figures 5 through 13 indicate

+ 1 o ranges. Points without bars represent

single determinations. The numerical values

of the data presented in these figures are listed in Tables 9-16

41
k/c

Figure 6. Experimental results on SRM 48l (Au-Ag) for

AuMa

.

42

k/c

44
45
46
47


Figure 13. Experimental results on SRM 482 (Au-Cu)

for CuLa.

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-=r vo

CO CM

po vo CO rH vo

rH rH CM CO ^J- o o o o o o

OA i—I VD oo-=r O i—1 i—I CM CO o o o o o

cr\ cm mmoM>

o coco -=r cm

-^T -^d" CO CM CM CM OO CO 0~\ CM CT\

LCA CM vo CO o

OO CO CM CM CM

VO VO OMOiCO rH oooo o o oo

OO OO CM CM rH CAW (TlOMTiOO OO CM CM rH

ir\ o o o o oo

rH CM OO^T -=T mooocorH cm 00^3- -^T H

s

t-3hO

56
rH C\J O O

o o o

I I

CM CM i—

o o o

o o o

i—I C\J C\J C\J o o o o

o o o o

VO CM '—1 C\J PO o oo O o o oo o

mvo o o

Q O

VO VO LCA o o o

o o o

vo i^co o o o o

o o o o

O O H H O

o o o o o o o o o o

+ 1+1+ + +

rH O

H rH o o

O OACO H O O

o o o O O OA CO

rH H O O

o o o o

VO OA OO C— OA OIHHHO o o o o o

o o

o o o o

O CM H

o o o

o o o

+ 1+1 +1+ +

o o o o

o o o o

o o o o

+ I+I+I+I

O OJ LO.CO O

O O O O rH o o o o o

3 o

Cm

OO LCA OJ OA OJ LCA OA OA OA OO CO t

CO rH O O O O o

I +

LfACO rH OHO O O O

CO coco oo

OA OA OO CO

oa lca oa-^t O H H H

o o o o

LCA OO OA i—I OA

OA.OO LXA^T OJ

o [>--=r c- oj cn <H O O r-1 o o o o o

o

o

rH CM VO VO CM t>- oj oo oo on oo oj

ooh oj^r CMOOO

o o o o

OJ O OAVO

OO^T OO 00

oo oo on oo LHO CM UA O i—I O CO VO

on on on cm oj

oo on rH H o vo

i—i on on on lca oj m en <yi cn <m cn

rH LOCO o

LO LTA LfA cn cn en cn

=T CM LTA on

on on o t— lca on on on cm cm

LPi O LCA O O OO

rH cm cm on-=r -=t O O O COcaj on-=r

LTA O O O O

rH CM OO-^T

57
OA CM O H o o H H O HHH o o o

o o o o

men o o o

o o o

on o VO o- o o H o H CM H

-p rH l—

1

o o o o o o o o o o

o o o o o o o o o o o o

oo

1 1 + 1 + 1 + 1 1 1 1

C\J rH o OA CO C\J vo C\J o C— LT\ m

H rH H o o m rH r—

1

rH o o o o o o o o o o o o o o o

H- + + + + + + + + + + + o o o 1—

1

CM rH C\J cn OA rH ^3- lovo

CL o o o o O O rH C\J CM m on on on o o o o o o o o o o o o o

3o

o

+ 1 + 1+1 I

OA CO VO on i—I LfA o

OA OA OA OA OA.CQ CO

CM LfA LfA LfAVD

rH O O O O

O O

CM rl CACMOI O (M ISO IS

CO LfA LTA^r en r-\ o

O rH LfA LfA VO

rH H (M H

O O O O

E£ CO O I PQ

CO VO D--CO rH CO vo Lf\-=r on cm o

On CM rH CM CM o o o o o

o o o o o

OA OA O LfA LfA CO 00 LfA i—I C

On CO LfA CM OA LfA On rH OAt— romincM c\i (\i cm h -

1

rod cm on cn i—I cm LfA ono o ,—i o o o o oo oooooo

o o r-\ m oovo O CO VO LfA -^3" i—I i—

I

LfA ^=r .=r

t>--=r^r LfA LfA c^— OA o VO rH

1—I O LfA CM OA^j- 1—I O VO VO ^r^ronmcMCMCMCMr-HrH

^1 CM LfA O LfA O O CO LfA t*— O CM LfA O LfA O O CO

rH rH CM CM 0O-=J" -^T rH rH rH CM CM On^T -=J"

CD 3

•H

Cu 58
Table 17. Mass absorption coefficients used In the preparation of Tables 13 to 16

Cu Au Sources: [23] [22] [23] [22]

Line

CuKa 53-5 52.8 208 210

CuLa 2079* 1907 7030* 8l8l

AuMa 2034 2025 1124 1016

AuLcu 246 245 128 132

AuL3^ 158 162 83.4 89.2

*Values obtained by extrapolation

Ag Au Sources: [23] [22] [23] [22]

Line

AgLa 522 540 1961 2155

AgL 3"n 466 477 2052 2059

AuMa 1266 1277 1124 1016

AuLa

x 130 130 128 132

Table 18. Mean excitation potentials

Element

Cu Ag Au Source

[21] 314 487 797

[16] 377 637 1071

59
APPENDIX 2 CERTIFICATES OF ANALYSIS FOR SRM'S 48l AND 482

60
U. S. DepartAwm*' of Commerce

MauricllJ!. Stans Certificate of Analysis

Standard Reference Material 481

Gold-Silver Wires for Microprobe Analysis

These standard reference materials are designed for use in quantitative elemental microprobe analysis. Although the selection of this particular system was circumscribed by

the requirements of standard reference materials for electron probe microanalysis, the

materials will be equally useful for other micro techniques. Accurate chemical characteriza- tion and the achievement of homogeneity on a microscopic scale was given special emphasis. SRM 481 Color Nominal Cominco U.S. Bureau Average

wire code comp American a of the Mint b NBSC Value d Au Au Ag Au Ag Au Ag

Percent by weight A Gold AulOO 100.00 B Gray Au80-Ag20 80.00 80.02 20.00 80.13 19.93 80.0

5 19.96 C Yellow Au60-Ag40 60.01 60.11 39.85 60.04 39.98 60.0

5 39.92 D Blue Au40-Ag60 39.99 40.03 59.90 40.06 59.96 40.0 3 59.

3 E Red Au20-Ag80 22.42 22.42 77.59 22.46 77.56 22.4 3 77.58 F Silver AglOO 100. o

0

a The fire assay method was employed for the determination of Au by Cominco American.

b At the U.S. Bureau of the Mint, Au was determined by fire assay and Ag was determined by titration as AgCl.

c At NBS, Au was determined from the residue after treatment of the alloys with HN03

. The Au residue was dissolved in aqua regia, filtered, the Au precipitated by sulfurous acid, and weighed. Ag was determined gravimetrically as AgCl in all four alloys, and also coulometrically in the 80 percent Ag alloy.

d The results of individual laboratories agree within a range of ±0.1 percent absolute from

the average values. The agreement between results by the different methods and analysts, and the summation of results close to 100 percent for each binary alloy, indicate that the

averages are free from significant bias. The set of standard reference materials, SRM 481, consists of six wires each having a diameter of approximately 0.5 mm and a length of approximately 5 cm. For identification, the four alloy wires were covered with an easily removable colored coating. The overall direction and coordination of technical measurements leading to certifica- tion were performed under the chairmanship of B. F. Scribner. The technical and support aspects involved in the preparation, certification, and

issuance of these standards were coordinated through the Office of Standard Reference

Materials by R. E. Michaelis. Washington, D. C. 20234 W. Wayne Meinke, Chief February 14, 1969 (over) Office of Standard Reference Materials

61
PREPARATION AND PURITY: The standards were prepared by Cominco American Inc. in the form of wires approximately 150 meters long. The end members of the series, as well as the

starting materials for the alloys, were of the highest purity grade and precautions were taken

to minimize contamination. Two of the alloy standards were heat-treated at NBS to improve

microhomogeneity. The pure metal standards were examined by the residual resistivity ratio technique and the total of electrically active impurities in each was estimated to be about

0.001 percent. The gold-silver wires were examined spectrographically for metallic impurities; no significant impurities were found at detection limits ranging from 0.0001 to 0.010 percent. Longitudinal Homogeneity: Variation in composition along the full length of each alloy wire was investigated by electron probe microanalysis for areas 25 fim diameter on cross sections at three to five positions along the wire including the two ends. The observed

differences in composition for the positions, expressed as the range between the highest and

lowest values for each alloy, were as follows:

Nominal Composition Au80 Au60 Au40 Au20

Observed rangel 0.3% 0.6% 0.3% 0.5%

Homogeneity along the wires was also tested by measurement of the residual resistivity

ratio. These measurements indicated that the variation (macroscopic) of composition along

all standard wires was less than 0.1 percent absolute. Further information on longitudinal homogeneity of the wires was obtained by determinations of Au at the extreme ends of the

alloy wires by the Bureau of the Mint; the data also indicate that the extreme variation along the wires is less than 0. 1 percent absolute. Transverse and Micro Homogeneity: Variation in composition within the above mentioned cross sections of the wires was investigated by electron probe microanalysis. For each

cross section, measurements were made along two diagonals at right angles. On each

diagonal, determinations were made at 25 points, 1 {im or less in diameter, starting and

ending at approximately 25 nm from the edge. For each alloy, the element which could be determined with the better precision was used in the evaluation. The variation was

calculated in terms of the standard deviation for an individual determination for each

traverse. In the table below, the variation is presented as the range between the lowest and

highest observed standard deviations for the six to eight traverses performed on each alloy.

Range of Standard Nominal Composition Element Determined Deviation for Traverses3 Au80 Ag 0.08-0.11%

Au60 Au .08- .16 Au40 Au .08- .13 Au20 Au .12- .37

62
The homogeneity on a microscopic scale was further investigated by performing

quantitative measurements in two arrays of 10 x 10 points (1 ptm diameter) on each of the

cross sections. The distance between adjacent points was 3.5 /-im. This was repeated on

several cross sections so that 6 to 8 arrays were obtained on each alloy. For the element which could be measured with better precision, the range is given between the lowest and

highest observed standard deviation for an individual determination for the 6 to 8 arrays for each alloy. Range of Standard Nominal Composition Element Evaluated Deviations for Arrays3 Au80 Ag 0.09-0.15%

Au60 Au .18- .57 Au40 Au .19- .25, Au20 Au .11 - .66

(Note: This range and the two ranges in the following tables are close to the precision of

the method and should be considered upper limits of estimates of inhomogeneity.)

Extensive homogeneity studies were performed with the electron probe microanalyzer

at NBS by M. A. Giles, R. L. Myklebust, C. E. Fiori, and K. F. J. Heinrich. Measurements of

residual resistivity ratio were made at NBS, Boulder, Colorado, by R. L. Rutter, J. G. Hust, and R. L. Powell. Heat treatment of the alloys at NBS was performed by G. E. Hicho and

M. R. Meyerson. Spectrographs survey analyses were made at NBS by V. C. Stewart. Determinations of composition were made at Cominco American, Inc., Spokane, Washington, by T. A. Rice; at the U.S. Bureau of the Mint, Washington, D. C, by

H. G. Hanson, Jr.; and at NBS by R. A. Durst, G. Marinenko, and C. E. Champion.

63
U. S. Depa: Mauric

of Commerce

Stans

7 Certificate of Analysis

STANDARD REFERENCE MATERIAL 482

Gold-Copper Wires for Microprobe Analysis

These standard reference materials are designed for use in quantitative elemental microprobe

analysis. Although the selection of this particular system was circumscribed by the requirements

of standard reference materials for electron probe microanalysis, the materials will be equally

useful for other micro techniques. Accurate chemical characterization and the achievement of homogeneity on a microscopic scale were given special emphasis. SRM 482 Color Nominal Cominco U.S. Bureau Average

wire code composition American 3 of the Mintb NBSC value d Au Au Cu Au Cu Au Cu

Percent by weight A Gold AulOO 100.00 B Gray Au80 - Cu20 80.10 80.13 19.81 80.21 19.85 80.

1

5 19.8 3 C Blue Au60 - Cu40 60.30 60.37 39.66 60.41 39.62 60.

3

6 39.64 D Yellow Au40 - Cu60 40.12 40.06 59.88 40.11 59.97 40. lo 59.92 E Red Au20 - Cu80 20.04 20.12 79.84 20.21 79.86 20.

1

2 79.85 F Copper CulOO 100.

0

0

a The fire assay method was employed for the determination of Au by Cominco American.

b At the U. S. Bureau of the Mint, Au was determined by fire assay and Cu was determined by

electrodeposition.

c At NBS, Au was determined by precipitation from solution; Cu was determined by electro- deposition.

d The results of individual laboratories agree within a range of ±0.1% absolute from the average

values. The agreement between results by the different methods and analysts, and the summation

of results close to 100% for each binary alloy, indicate that the averages are free from significant

bias.The set of standard reference materials, SRM 482, consists of six wires each having a diameter

of approximately 0.5 mm and a length of approximately 5 cm. For identification, the four alloy wires were covered with an easily removable colored coating. The overall direction and coordination of technical measurements leading to certification were

performed under the chairmanship of B. F. Scribner. The technical and support aspects involved in the preparation, certification, and issuance of

these standards were coordinated through the Office of Standard Reference Materials by

R. E. Michaelis.

Washington, D. C. 20234

June 6, 1969

(over)

W. Wayne Meinke, Chief

Office of Standard Reference Materials

64
Preparation AND Purity: The standards were prepared by Cominco American, Inc. in the form of

wires approximately 150 meters long. The end members of the series, as well as the starting materials for the alloys, were of the highest purity grade and precautions were taken to minimize

contamination. Two of the alloy standards were heat-treated at NBS to improve microhomogeneity. The pure metal standards were examined by the residual resistivity ratio technique and the total of

electrically active impurities in each was estimated to be about 0.001%. The gold-copper wires were examined spectrographically for metallic impurities; no significant impurities were found at detection limits ranging from 0.0001 to 0.010%. Longitudinal HOMOGENEITY: Variation in composition along the full length of each alloy wire was

investigated by electron probe microanalysis for areas 25 um diameter on cross sections at three

positions along the wire including the two ends. The observed differences in composition for the

positions, expressed as the range between the highest and lowest values for each alloy, were as follows: Nominal Composition Au80 Au60 Au40 Au20

Observed range* 0.3% 0.7% 0.9% 0.9%

Homogeneity along the wires was also tested by measurement of the residual resistivity ratio. These measurements indicated that the variation (macroscopic) of composition along all standard

Wires was less than 0.1% absolute. Further information on longitudinal homogeneity of the wires was obtained by determinations of Au at the extreme ends of the alloy wires by the Bureau of the Mint; the data also indicate that the extreme variation along the wires is less than 0.1% absolute. TRANSVERSE AND Micro HOMOGENEITY: Variation in composition within the above mentioned cross sections of the wires was investigated by electron probe microanalysis. For each cross section, measurements were made along two diagonals at right angles. On each diagonal, determinations were made at 25 points, 1 fim or less in diameter, starting and ending at approximately 25 pirn from

the edge. For each alloy, the element which. could be determined with the better precision was used

in the evaluation. The variation was calculated in terms of the standard deviation for an individual determination for each traverse. In the table below, the variation is presented as the range between

the lowest and highest observed standard deviations for the six traverses performed on each alloy. Nominal Element Range of Standard Composition Determined Deviations for Traverses* Au80 Cu 0.09 - 0.24% Au60 Cu .16- .27 Au40 Au .13- .23 Au20 Au .13- .20

65
The homogeneity on a microscopic scale was further investigated by performing quantitative measurements in two arrays of 10 x 10 points (1 urn diameter) on each of the cross sections. The

distance between adjacent points was 3.5 /im. This was repeated on several cross sections so that 6

arrays were obtained on each alloy. For the element which could be measured with better precision, the range is given between the lowest and highest observed standard deviation for an individual determination for the 6 arrays for each alloy. Nominal Element Range of Standard Composition Determined Deviations for Arrays4 Au80 Cu 0.19 - 0.28% Au60 Cu .28- .37 Au40 Au .25- .31 Au20 Au .12- .20 *The ranges indicated are close to the precision of the method and should be considered upper

limits of estimates of inhomogeneity.

Extensive homogeneity studies were performed with the electron probe microanalyzer at NBS

by M. A. Giles, D L. Vieth, R. L. Myklebust, C. E. Fiori, and K. F. J. Heinrich. Measurements of

residual resistivity ratio were made at NBS, Boulder, Colorado, by R. L. Rutter and R. L. Powell. Heat treatment of the alloys at NBS was performed by G. E. Hicho and M. R. Meyerson. Spectrographs survey analyses were made at NBS by V. C. Stewart. Determinations of composition were made at Cominco American, Inc., Spokane, Washington, by T. A. Rice; at the U. S. Bureau of the Mint, Washington, D. C, by H. G. Hanson, Jr.; and at NBS by J. R. Baldwin and R. A. Durst.

66
APPENDIX 3 PRELIMINARY HOMOGENEITY TESTING

The preparation, homogenization, and preliminary homogeneity testing of the Au-Ag and Au-Cu alloys extended over

a period of more than two years. This Appendix summarizes

the preliminary analyses performed during preparation of

the alloys. Important points have been extracted from the

many reports written during this period and are presented

in chronological order.

Pinal characterization of composition and homogeneity

is discussed in Sections Three and Four, respectively.

Dec. 23, 1966 The following materials and assay reports

(Au-Ag) were received from Cominco American, Inc. Ca Fe_ Mg_ Si Ag Al Pb Ni

6-9' s Cu 0.1* 0.1 1.0 0 .2 1.0 2 . 0 6-9' s Ag 0.3 1.0 0.5 0 .2 1. 0 0.1 0.5

6-9' s Au 0.3 1. 0 0.7 0.3 0.7 0.1 0.3

*A11 values are in ppm

Alloys Mass fraction Au Au20-Ag80

Au60-Ag4 0 Au8 0-Ag2 0 Au40-Ag60

0.1999

0 .6001

0 .8000

0.3999

Note: No significant differences in the impurity levels

between the alloys and the pure elements were observed.

April 25, 1967 The following materials and assay reports were received from Cominco American, Inc.

67
Alloys Mass fraction Au Au60-Cu40 0.603

Au80-Cu20 0.801

Au20-Cu80 0.199

Au40-Cu60 0.401

Note: No significant differences in the impurity levels

between the alloys and the pure elements were observed.

June 7, 1967 An NBS report on the homogeneity of the Au20-Ag80

(Au-Ag) alloy concluded that this alloy was unacceptable

due to a gold-enriched layer 3 0 ym thick at the

surface of the wire

.

Oct. 19, 1967 An NBS report on the homogeneity of the Au20-Ag80

(Au-Ag) alloy found this alloy to be macroscopically

homogeneous along the length of the wire. It was, however, microscopically inhomogeneous

across the cross-section and therefore unusable.

Oct. 25, 1967 An NBS report on the homogeneity of the Au80-Ag20

(Au-Ag) alloy found this wire to be homogeneous to within 0.005 both along the wire and across the

cross-section, except for a very thin region

near the edge.

Oct. 27, 1967 The Au20-Ag80 wires were submitted to a homo-

( Au-Ag) genization heat treatment at NBS. Nov. 8, 1967 An NBS report on the homogeneity of the Au4 0-Ag60

(Au-Ag) alloy found this wire to be homogeneous to within 0.005 along the length but inhomogeneous

across the cross-section.

(This material was later given the same homogenizat ion heat

treatment as the Au2 0-Ag80.)

Nov. 28, 1967 Electronic characterization (residual resis-

(Au-Ag) tivity ratio) was performed at NBS on two of

the alloys. The Au80-Ag20 was homogeneous

to within 0.002 and the Au60-Ag40 was ten times worse (0.02).

Feb. 29, 1968 Electronic characterization was performed on (Au-Cu) the Au-Cu alloys at NBS with the following

result s

.

68
Alloy Homogeneity Range

Au80-Cu20 0.002

Au60-Cu40 0.0015

Au20-Cu80 0.002

Au40-Cu60 not done - wire too brittle

March 4, 1968 Cominco American, Inc. replaced the Au20-Ag80

( Au-Ag) alloy.

March 14, 1968 Electronic characterization of the pure Au,

Agj and Cu was performed at NBS. Total impurities in each metal are about 10 ppm.

May 24, 1968 Electronic characterization of the new Au20-Ag80

(Au-Ag) alloy at NBS concluded that it was homogeneous

to within 0 . 002

July 3 3 1968 A chemical analysis at NBS was performed on the

(Au-Cu) Au40-Cu60 alloy after a homogenization heat

treatment. The mass fractions of Au in two

samples were 0.4017 and 0.4013; therefore, no

Cu was lost.

Aug. 16, 1968 A chemical analysis was performed at NBS on (Au-Cu) the Au20-Cu80 alloy both before and after a homogenization heat treatment.

Au before treatment - 0.2021

Au after treatment - 0.2022

Dec. 16, 1968

(Au-Cu) and

(Au-Ag)

Electronic characterizations were performed

at NBS on the following alloys.

Alloy

Au40-Cu60

Au40-Ag60

Au20-Ag80

Homogeneity Range

0.001

0.002

0. 002

Feb. 6, 1969 Cominco American, Inc. assayed the new Au20-Ag80

(Au-Ag) alloy as 0.2242 Au

April 22, 1969 An optical spect rographic analysis at NBS of

(Au-Cu) the Au-Cu alloys found the following impurities

in each.

Ag <0. 00001, Mg <0. 00001, Pb <0. 00001, and

Si <0.0001.

69
APPENDIX 4 AUTOMATED TECHNIQUES FOR HOMOGENEITY ANALYSIS

In the preparation of any standard reference material,

characterization of composition uniformity is essential.

This is to insure that each standard is, within specified

limits, the same as any other standard of the same type.

In addition, characterization of homogeneity on a microscopic

scale is required in the case of standards for microprobe

and other micro-analytical techniques. After consultation

with other microprobe analysts, we set a goal of producing

standards in which the range of concentrations, on either a macro- or micro-scale, do not exceed 0.01. The quantity of

data necessary to establish the micro-homogeneity of the two

sets of standards described in this report was large (more

than 36,000 determinations) and prompted development of the

automated data acquisition system and computer program described in this section.

A . Instrumental

An automated data acquisition system [27, 28], referred

to as a matrix scanner, has been developed to direct the

electron probe beam to different locations on a specimen

and to record quantitative analytical data associated with

each location. The matrix scanner can be preset to examine

test locations arranged in either a straight line or in a two-dimensional grid (raster) . The latter arrangement con- serves the digital quantitative nature of the information

obtained in single-point analysis while providing topographic

coverage analogous to continuous area scanning of low resolution.

A schematic block diagram of the matrix scanner is given

in Figure 14, and the front panels of the electronic modules

are shown in Figure 15 . Before examining the details of

operation for individual electron modules, it is helpful to

70
TIMER SCALER SCALER

SCALER SCALER

PROGRAM

CONTROL

SCANNER PAPER TAPE

PUNCH

Figure 14. Block diagram of the matrix scanner.
Figure 15. Front view of the matrix scanner.

72
consider the overall sequence of matrix scanner operation.

This operation is summarized in Figure 16. The analyst first selects a one- or two-dimensional

array of points (line or raster) for the problem under investigation. Through the program control unit, he predetermines

the dimensions of the array as well as other parameters of

the operation. At the start of the analysis, the program

control directs the beam positioner to deflect the electron

beam to the first position of the preselected array. The

timer-sealer block is directed to record the signals produced

at the x-ray detectors, as well as beam or monitor current

signals, for a fixed time period or until a preset integrated

current level is attained. At the end of the counting period,

the information accumulated in the scalers and timer is

punched on paper tape. After this, the program control resets the timer and scalers, advances the electron beam to the next position in the array, and the counting phase is

repeated. All the points of the array are automatically

measured in this way. A selection switch on the unit permits

automatic repetition of the array a preset number of times.

The matrix scanner is composed of two functional subsystems. The data acquisition components are the print-out

control unit, timer, scalers, teletypewriter, punch driver,

and paper tape punch, while the matrix generator components

are the print-out control, x-y matrix module, and scan control unit. The print-out control, common to both subsystems,

functions as an interconnect ive module for the two subsystems.

Each component is compatible with AEC nuclear instrumentation

module (NIM) standards and all but three are "stock items"

which were available at the time the system was developed.

It was necessary for our electronics supplier, ORTEC, Inc. 1

,

"The mention of a supplier is for descriptive purposes only

and does not imply recommendation or endorsement by the

National Bureau of Standards.

73
START

>| BEGIN MATRIX SCAN ]

-H X-RAY COUNTING INTERVAL |

TRANSFER DATA FROM TIMER- SCALERS TO PAPER TAPE PUNCH

RESET TIMER SCALERS

| ADVANCE Y REGISTER I

! RESET Y REGISTER

| ADVANCE X REGISTER |

NO

[ RESET X REGISTER

| ADVANCE SCAN REGISTER

| STOP |

Figure 16. Sequence of automatic operations performed

by the matrix scanner.

74
[to especially construct the x-y matrix and scan control units

and to modify the print-out control to our specifications.

In the data acquisition subsystem, the print-out control

serves as a data scanner to transfer data from the scalers

land timer, one character at a time, to the teletypewriter

|or high-speed paper tape punch. In addition, it resets and

I restarts the scalers and timer in the proper sequence. A

| variety of signals, in addition to x-ray counts, can be

j integrated on the scalers; for example, monitor current or

j specimen current can be measured with the use of an analog-

| to-digital converter. When the 60 character/sec paper tape

: punch (Tally, Model 420) is utilized, a punch driver module

I is required in order to convert the low—level logic signals

| of the print-out control to a power level adequate to drive

;| the punch. All tapes, including those produced on the teleI

I typewriter (Teletype, Model 33) are punched in the ASCII code.

In the matrix generator subsystem, the print-out control

signals the x-y matrix module to advance to the next location

each time the timer reaches its preset limit. The x-y matrix

I unit generates a one- or two-dimensional matrix of variable

size (maximum 100 x 100 locations) . The registers of this

device advance one y position (column) along a given x (row)

after completion of each counting interval. When the preset

limit for number of columns is reached, the y-register is

returned to the first column and the x-register is advanced

to the next row. When the preset row limit is reached, the

scan control is checked and execution is stopped if the preset

number of scans has been reached; otherwise, both the x and

y registers reset to their initial points (0, 0), and the

j next scan begins. The outputs of the x-y matrix module are

i dc voltages for x and y, which are proportional to the

values of the registers (i.e., location). These voltages

are connected to the electron beam scanning system of the

electron probe and position the beam to the corresponding

75
location on the specimen. The distances between measured

points on the specimen can be varied over a wide range. In addition to storing the number of scans to be executed, the

scan-control unit also stores the number of scalers to be

read onto paper tape during each cycle.

Besides micro-homogeneity studies, the matrix scanner

can be used in a diversity of applications, including digital

wavelength scans, measurement of signal variation as a function

of time, and analysis of diffusion couples, inclusions in

alloys, and biological specimens. Since, in many cases, information from more than one x-ray channel or other signal

channel is available, the correlation of two or more channels

may be of interest. Furthermore, the similarity of this procedure with continuous raster scanning suggests that topographic relationships can be investigated. These may include

size and shape of single-phase regions, volume fractions

occupied by each of the phases, number of inclusions per unit

area, variation of composition as a function of distance to grain boundaries, etc. The matrix scanner can thus be used

in a wide variety of techniques by selecting the appropriate

array and scanning sequence, and by designing computation

programs for evaluating the output of this device.

B . Computation Technique

We have written a computer program, named TOPO, to receive

data collected with the matrix scanner and to perform the

computations essential to the study of micro-homogeneity for

binary alloys.

The data for micro-homogeneity studies are x-ray intensities simultaneously measured for two elements at each of

the locations in a two-dimensional grid, 10 x 10 locations

in this work. We refer to a set of data which contains one measurement for each of the elements at each of the grid

locations as one "scan"; several scans may be sequentially

76
j collected on the same grid using the same lines and operating

j conditions. This yields one "case" consisting of several

repetitive scans on a grid.

TOPO performs two major types of computations in analyzj ing micro-homogeneity. First , statistics are calculated for

j all the signal intensity data in a case, irrespective of location within the array. These include the mean, square root

| of the mean, and standard deviation. A frequency distribution

j of the intensities as a function of distance from the mean is

i computed and plotted, and, for the sake of comparison, the

; Poisson distribution with the same mean is presented. Plots

of the data are also given in the measurement time sequence,

to allow direct observation of time-dependent drifts.

Secondly, intensity variations are displayed as a

i function of location. The two-dimensional grid is graphically

t printed on the line printer and the intensity at each location

1 is represented by a symbol indicative of the corresponding

[ range of intensities. This topographical display is very

useful in examining the spatial distribution of any microI homogeneity. As a part of the topographical computation, we have written and included a subroutine for pattern analysis

which tests the topograph for the presence of patterns of con- nected locations having similar intensity levels. This type

of analysis is useful not only in homogeneity studies, but

also in reducing the data obtained using the matrix scanner

in a variety of other modes. Examples of such applications

would include studies of diffusion couples, grain boundaries,

and micro-inclusions [29]. In the next few paragraphs, we will describe, in somewhat more detail, the operation of TOPO

and illustrate its use by selected portions of its printout.

Parameters which specify the number of cases, size of

matrix, number of scans, background and pure element intensities, intensity-to-concentration conversion factor, and output

options are entered as a set of data cards with each submission of TOPO to the computer. The bulk of the data
(intensities for two elements at each matrix location) is

collected on paper tape by the matrix scanner and later

transferred to magnetic tape using a paper-to-magnetic tape

data converter. The magnetic tape is read by TOPO, one case

at a time.

The program TOPO and the 10 user subroutines which it

calls (PTLOAD, CHAR, ORTHO, FRAME , GRID, FREDIS, PLOT, PLOT2

,

PATRN, and RANDOM) were written in Fortran V language for

the Univac 1108. The total length of the program and 10 subroutines is about 2 000 cards , compilation time is about

15 seconds; and running time for 5 cases is less than 2 minutes. With minor modifications, principally to format statements, fixed-point conversions, and to that portion of the

program which loads the data (which are still in a paper tape

code) from the magnetic tape, this program can be adapted

for use with most Fortran IV compilers on computers having

at least 64,000 words of core storage.

At the beginning of processing for each case, PTLOAD is

called to load intensities for the given case. The intensities are read from a seven-channel magnetic tape and consequently, are not obtained as a direct image of the original

eight-channel paper tape; in the paper-to-magnetic tape conversion, the bits of each paper tape character are divided

into two magnetic tape characters. This necessitates bit-bybit interpretation in PTLOAD, and its internal subroutine

CHAR, and restoration of the original data format. Upon

completion of this processing, a complete listing of the

input data is printed.

Several statistics, including the number of observations,

mean, square root of the mean, and standard deviation, are computed and printed for the "raw" intensity data. Also, a frequency distribution of the intensities as a function of

distance from the mean and, for the sake of comparison, the

Poisson distribution with the same mean are presented as a 78
table. A graph of the frequency distribution is then displayed in the computer output. Finally, as a graphical test

for drift, plots of the intensities in measurement time

sequence are included. These computations and graphs are

j prepared in the subroutines FREDIS, PLOT, and PL0T2

After the statistics for "raw" intensities are computed,

program control is returned to TOPO where data correction and

'calibration computations are performed. The background

'correction and dead-time correction are made according to

J customary methods. The intensities corrected for these

two effects are used in a calibration equation to determine

'the concentration at each location; each element is processed

j in this way. The general calibration equation is:

I where i is a tally of measurements, I. and C. are the x-ray

1 1 intensity concentration at i, I and C

g are the x-ray intensity and concentration from a standard, and m is a proportionality constant relating the two ratios. The term m

i includes calibration for the effects of fluorescence,

absorption, and atomic number, and is determined from theory

or by empirical means prior to the beginning of the TOPO run.

In the application of TOPO, described in the next section of

this report, we know the average composition of each specimen;

and we used it as the standard. When this technique is

employed, we have, for each element, C

g = C and I

g = I, where

I is the mean x-ray intensity over the entire matrix and C is the given mean concentration for the element. In addition,

we used the approximation that the two ratios given in equation

j (1) are directly proportional, i.e., that m=l . When these

i three substitutions are made in equation (1) and it is solved

for C, we obtain the calibration equation used in this work:

I. /I =

l s m • C./C , l s

3 (1)

C. = C • I./I. (2)

79
The ' s obtained by equation (2), are next corrected

for effects of linear and quadratic terms of drift as a function of measurement sequence time, and the effect of over- lapping successive scans on the same specimen array. The

effect of each of these terms is expressed as a coefficient,

here called a., where the subscript j labels the coefficient

J with respect to the effect it represents. Coefficient a^ is

the mean concentration and if no other effects or biases were present, i.e., the other coefficients were zero, then

would be the same as a^. The coefficients a

2 and a^ contain

the drift effects, while all the remaining a's, one fewer than

the total number of scans, express scan-overlap effects. The

necessity for corrections of the latter type arises because

of the possibility of specimen contamination during electron

probe analysis. Such contamination may be increased on suc- cessive scans and thereby have a different effect on the measured intensities in each scan after the first. All the a coefficients are determined by substituting the C's obtained

in equation (2) into the set of equations:

In these equations, C and i have the same definition as before,

t is measurement sequence time, k is a counter which indexes

the scan within which the i— measurement is located, r is a switch which indicates the presence of a scan-overlap condition, and 6 includes the error from Poisson and non-Poisson

sources and, most importantly, any inhomogeneity present at the point. Where n is the number of scans and p Is the number

of locations per scan, we have as limits for I and mathematical definitions for k and r:

n+2

1 < I < np, (4) k = INT (i/p) + 1, (5)

80
r. k

= 0 if k < j-2, and (6) rJk

= 1 if k > j-2. (7) In equation (5) 3 the function INT computes the closest integer

which is less than the argument. The method for determining

a's in equation (3) is a conventional least squares regresj sion; in this case, the fit is selected to minimize the sum

j of the squared values of the deviations in the C's. The reI gression computation is performed In the subroutine ORTHO.

! Following these corrections, statistics similar to those comj puted for the "raw" data are calculated and displayed (See

Figure 17 and 18).

When multiple scans are obtained, average C's are calculated for each specimen location. The topographic displays

are produced in two ways, relative and absolute. In the

relative topograph, local deviations for the mean concentration are displayed by arbitrary symbols using the standard

deviation as a scale. Examples of relative topographs appear

in Figure 19; the key indicates the scale of deviation from

the mean. The range of +1 standard deviation is left blank

because we are mainly interested in observing which locations

lie outside that range. The relative topograph is especially

useful for comparing results on elements at two different

concentration levels; because the standard deviation is used

as the scale unit, all relative topographs have the same approximate coverage in each scale range. Subroutines FRAME

and GRID are used in the printout of the relative topographs

and the absolute topographs. Absolute topographs show the

local deviation in concentration from the mean, using symbols

which designate concentration ranges on an absolute scale.

In analysis of micro-homogeneity, the importance of these

two types of topographs lies in the fact that they can be

examined for patterns (groupings) of locations of similar

concentration level. These examinations, which were performed

81
ELEMENT MJ MB EP I 2 THE STATISTICS ON THE NEXT FOUR PAGES TREAT

PRES. DIST. VS CUMULATIVE NUM3EP BELOtf OP =

NUM 3ER MEAN

SIGMA

DRIFT AND OVERLAP CORRECTED INTENSITIES

100

1S1 191. 95 0 37 3. 061

QR 3 T MEAN*. 401.48 7 NO 3EL0 W PCT. IN NO . K M+-K*SQR<M) PCT. BELOW POISSON ORr INCRE ME NT IN CRE^ -3.0 0 15 99 37 .4 90 0 .000 . 100 0. .00 0 3 • -2 .6 5 160121.3230 . 00 0 .400 0. .000 0.

-2 .32 160255 .1 500 1 . 000 1.00 0 1. 1.000 I

.

-1 .9 9 1603 33 .9 800 2. 00 0 2 . 30 0 2 . 1 . 00 0 1 . -1 .66 16 05 22 .8000 6.000 4. 800 6. 4.000 4 . -1 .32 1606 56 .6300 6. 00 0 3. 200 6. .000 0. .99 150790.4600 12. GOO 1 5. 90 Q 12. 6 . CO 0 6 .

. 5 b 160S24 .2 900 22.000 25.230 22. 1 0.00 0 10.

.32 16 1053 .1 100 3 9.00 0 37. 100 39. 17.000 17.

.0 0 16 11 31 .9400 5 0. 300 50. 000 50. 1 1.03 0 11 . .3 3 16 1325.7800 60. 000 6 2. 900 60. 1 0.00 0 10 . .6 7 16 1459 .6000 76.000 74. 800 76. 16.000 16 . 1 .00 16 15 93 .4 300 66. 000 84. 100 8 8. 1 2.00 0 12 . 1 .3 3 15 1727 .2600 91.000 30. 800 9 1. 3.U0 0 3 . 1 • 8 7 161861 .0800 95.000 9 5. 20 0 9 5. 4.00 0 4 . 2 .00 16 19 94 .9100 99. 000 9 7. 70 0 9 9. 4.000 4 . 2 .33 15 21 28 .7400 93. 000 99. 000 33. .00 0 0 . 2 .o 7 162262.5700 130.000 93. 600 100. 1.000 1 . 3 .0 0 16 2396 .3 900 100. 000 39. 90 0 100. .00 0 0 .

NU MBER OF ITEMS ABOVE +3*SQR OF ME AN - 0.

Figure 17- Statistics for . 6 Au in a .6 Au - .4 Ag

binary

.

82
83
13 X 10 MATRIX SCAN FOR SO AU 20 A3 20 KV 3 RELATIVE TOPOGRAPH

ELEMENT 1 = A 6 LA ELEMENT 2- AU LA

KEY

-4 5 -35 -25 -IS 0 +1S +25 +35 + * 5

5 0 : . 3LANK - + *

Figure 19. Relative topograph for the case given in

Figure 17.

at first by the investigator, can now be done automically by means of a subroutine we call PATRN. PATRN classifies

clusters of locations (separating positive from negative in

the current version) as to size. Then it determines the total

number of clusters within each size class. Cluster size is not simply defined as the number of locations connected in

a cluster, but is weighted as a function of the "compactness"

of the cluster. This is done by counting the links (diagonal

links are included) between the locations in a cluster (See

Figure 20). Entrance to the first location of a cluster is

counted as a link so that single points will be of size 1.

84
CLUSTER SIZE: 4

Figure 20. Method of defining cluster size by count in; links. Note extra weight given for

" compactnes s

.

A part of PATRN is designed to show if the amount of

structure observed differs from that which would, with significant probability, randomly occur. To make this test,

we scramble the array. The resulting pattern is analyzed

and then the random-assignment process is repeated, again

followed by analysis. The complete operation of randomassignment and analysis is repeated until 10 random patterns

have been evaluated. This information can then be compared

with that obtained directly from the observed pattern (See

Figure 21)

85
DAT

0 F LINKS

NON-PA NO OMIZ ED ELEMENT 1 ELEMEN T 2 POS . NEG. POS. H £6 . S IZE NO . SIZE NO. SIZE NO. SIZE NO.

13 17 m 16

1 1 1 2 1 5 1 4

2 1 2 G 2 1 2 3

3 D 3 0 3 0 3 2

'4 Q a 4 2 4 0 15 1 1 5 a is o 15 0 29 0 2 9 1 2 9 0 29 c

PAT T E R N ANALYSIS

0 F LINKS

MONTE CARLO DISTRIBUTION (10 SETS)

ELEMENT 1 ELEMENT 2

p OS . NEG. POS. NES . 5 IZE NO . SIZE NO. SI ZE NO. SIZE NO

1 10.40 1 9.80 1 5 .40 1 8.80

4.10 2 3.20 2 3 .60 2 3. 60

.9 0 3 1 .20 3 .4 0 3 1.90

4 1 .00 4 .SO 4 .90 4 . 70

5 .50 5 .40 5 .30 5 .60

6 .00 6 .40 6 .70 6 . 10

7 .2 0 7 .10 7 .10 7 .00

8 .10 8 . 00 8 .00 8 . 20

3 .30 9 .10 9 .2 0 9 .00

10 .10 10 .10 10 .00 10 . 10

11 .10 1 1 .20 11 .00 1 1 .00

13 .10 1 3 • 00 13 .00 1 3 .00

8 72 37 04 93 4

Figure 21. Pattern analysis for the relative topograph

in Figure 19- Notice that a strong pattern

is indicated for element 1 (Ag) s while the

analysis for element 2 (Au) shows a lack of

clustering; i.e., structures similar to those

found are likely to occur by chance.

86
We now introduce two other topographs which show sum

and difference correlations. In the case of the sum correla-

' tion topograph, the algebraic sum of the two absolute topo-

| graphs is computed and displayed on a point-by-point basis,

j Similarly, for the difference correlation topograph, the

algebraic difference of the two absolute topographs is computed and displayed on a point -by-point basis. In a binary

| alloy, any increase in the concentration of one element at a

j point must be accompanied by a decrease in the second element

I at the same point. If this correlation is not observed, I.e.,

if both elements decrease, or if one decreases with no change

observed for the second, the presence of a third element may

j be indicated. This is not a certain result because the

j changes could be caused by instrumental difficulties. Ini strumental problems are certainly suspect if both elements

j increase at a given location.

An alternative method for examining these correlations

is show in Figure 22. Here the departure from the mean at each location is plotted for both elements along orthogonal

l axes. Figure 23 illustrates several of the possible outcomes

for such plots. A nearly circular grouping centered on the

origin indicates a homogeneous binary alloy and measurements

of equal precision for both elements. Elliptically shaped

scatter about either of the axes means the precision was poorer for the element plotted on that axis. Negative correlation, that is, an increase in one element when the other

decreases, is a condition necessary for concluding that inhomogeneity is observed. Positive correlation results when

experimental errors are common to both elements and affect

them in the same direction (e.g., short duration beam

intensity fluctuation).

87
13 X 10 MATRIX SCAN FOR SO AU 20 AS 20 KV 3 CORRELATION GRAPH

ELEMENT 1 IS PLOTTED ON THE ORDINATE (VERT) AND ELEMENT 2 IS PLOTTED CN THE ABSCISSA (HORZ).

FOR EACH AXIS THE SCALE IS FROM -1.52 TO -a.5%.

1

1 13

1 2.2.3

1

1 2

2 1 7 13

1.2.3

12 13

1 1 5

1 2

2 1 2 1

7 1

Figure 22. Correlation graph for the case given in

Figure 17. Deviations from the mean Ag

concentration are plotted on the ordinate

while the deviations from the mean Au con- centration are plotted on the abscissa.

Deviations for neither element exceed 0.004,

indicating good homogeneity.

88
^11 IIP*

Figure 23. Four possible outcomes for the correlation

graphs. The conditions indicated by these

graphs are described in the text.

89

NBS-114A d-71

U.S. DEPT. OF COMM. IIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS-SP-260-28

Gov t Accession No.

3. Recipient's Accession No.

TITLE AND SUBTITLE Standard Reference Materials:

Preparation and Evaluation of SRM's U8l and U82 Gold-Silver

and Gold-Copper Alloys for Microanalysis

5. Publication Date August 1971

6. Performing Organization Code

^ author(s) Kurt F. J. Heinrich, Robert L. Myklebust, Stnaley D, Rasberry, and Robert E. Michaelis

8. Performing Organization

10. Project/Task/ Work Unit No. 310 2127

. performing organization name and address national bureau of standards department of commerce

washington, d.c. 20234

11. Contract/Grant No.

I. Sponsoring Organization Name and Address 13. Type of Report & Period Covered Final 1968-1971

14. Sponsoring Agency Code SUPPLEMENTARY NOTES

|6. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

| bibliography or literature survey, mention it here.)

I The reasoning behind the choice of the systems Au-Ag and Au-Cu for SRM's, and their

suggested uses are described. We also report on the preparations of the materials,

their chemical analysis, the tests performed to ascertain macroscopic and microscopic

homogeneity, and on relative x-ray intensity measurements at various x-ray lines and

voltages, A description of the instrumentation (matrix scanner), techniques, and

programs employed in the homogeneity studies, as well as tables and graphs of the

x-ray intensity measurements, are appended.

7. KEY WORDS (Alphabetical order, separated by semicolons) Alloys; corrections; electron probe; homogeneity; matrix scanner; microanalysis

quantitative analysis; standard reference materials; x-ray emission.

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