Bureau of Standards

rary, N.W. Bldg

FEB 1 4 1966

Reference book not to be

taken from the W i . NBS

ecknlccLL ^^ot& 272

i

|i^CTROCHEMICAL ANALYSIS: OPTICAL SPEaROMHRY,

T-RAY FLUORESCENCE SPEaROMETRY, AND ELECTRON PROBE

MICROANALYSIS TECHNIQUES

JULY 1964 TO JUNE 1965

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards is a principal focal point in the Federal Government for assuring

maximum application of the physical and engineering sciences to the advancement of tedinology in industry and commerce. Its responsibilities include development and maintenance of the natioiial stand- ards of measurement, and the provisions of means for making measurements consistent with those standards; determination of physical constants and properties of materials; development of methods

for testing materials, mechanisms, and structures, and making such tests as may be necessary, particularly for government agencies; cooperation in the establishment of standard practices for incorporation in codes and specifications; advisory service to government agencies on scientific and technical problems; invention and development of devices to serve special needs of the Government; assistance

to industry, business, and consumers in the development and acceptance of commercial standards and

simplified trade practice recommendations; administration of programs in cooperation with United

States business groups and standards organizations for the development of international standards of

practice; and maintenance of a clearinghouse for the collection and dissemination of scientific, technical, and engineering information. The scope of the Bureau's activities is suggested in the folio -it t

listing of its four Institutes and their organizational units.

Institute for Basic Standards. Applied Mathematics. Electricity. Metrology. Mechanics. HeaL

Atomic Physics-. Physical Chemistry. Laboratory Astrophysics.' Radiation Physics. Radio Standards

Laboratory:* Radio Standards Physics; Radio Standards Engineering. Office of Standard Reference

Data. Institute for Materials Research. Analytical Chemistry, f'oiymers. Metallurgy. Inorganic Materials. Reactor Radiations. Cryogenics.* Materials Evaluation Laboratory. Office of Standard Refer- ence Materials. Institute for Applied Technology. Building Research. Information Technology. Performance Test Development. Electronic Instrumentation. Textile and Apparel Technology Center. Technical Analysb.

Office of Weights and Measures. Office of Engineering Standards. Office of Invention and Innovation.

Office of Technical Resources. Clearinghouse for Federal Scientific and Technical Information. **

Central Radio Propagation Laboratory.* Ionospheric Telecommunications. Tropospheric Teie- communications. Space Environment Forecasting. Aeronomy.

* Located at Boulder, Colorado 80301. ** Located at 5285 Port Royal Road, Springfield, Virginia 22171.
NATIONAL BUREAU OF STANDARDS

Technical Note 272

ISSUED OCTOBER 21, 1965

SPECTROCHEMICAL ANALYSIS: OPTICAL SPECTROMETRY,

X-RAY FLUORESCENCE SPECTROMETRY, AND ELECTRON PROBE

MICROANALYSIS TECHNIQUES

JUNE 1964 TO JUNE 1965

Edited by Bourdon F. Scribner

Spectrochemical Analysis Section

Analytical Chemistry Section

Institute for Materials Research

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

listed or referred to in the open literature.

For sale by the Superintendent of Documents, Government Printing Office

Washington, D.C., 20402 - Price 50 cents

7

II
FOREWORD

The Analytical Chemistry Division was established as

a separate division at the National Bureau of Standards

on September 1, 1963 and became part of the Institute for

Materials Research in the February 1, 1964 reorganization.

It consists at present of seven sections and about 85

technical personnel encompassing some 30 different analytical competences from activation analysis and atomic

absorption to vacuum fusion and x-ray spectroscopy. These

competences, and in turn the sections which they comprise,

are charged with research at the forefront of analysis as

well as awareness of the practical sample, be it standard

reference material or service analysis. In addition it is

their responsibility to inform others of their efforts.

Formal publication in scientific periodicals is highly Important. In addition, however, it has been my experience that Informal, annual summaries of progress describing efforts of the past year can be very valuable in

disseminating infoinnation. At the National Bureau of

Standards such publications fit logically into the category of Technical Note. In 1965 we plan to issue these

summaries for all of our sections. The following is the

first annual report on progress of the Spectrochemlcal

Analysis Section.

W. Wayne Meinke, Chief

Analytical Chemistry Division

11
PREFACE

This is the first of a series of annual progress

reports of the Spectrochemical Section of the Analytical

Chemistry Division, The Section, formerly known as

Spectrochemistry, was established in 1948 as an outgrowth

of an extensive program of spectrochemical analysis of

uranium and related materials and also in recognition of

the growing importance of instrximental analysis. While the

Section had been primarily concerned with optical emission

spectrometry, the growing importance of x-ray spectrometry

for elemental analysis led to extension into this

complementary field in 1957* and to the addition of research

and application of electron probe microanalysis this year.

The purpose of the Section is to develop measurement

techniques for determining the composition of materials

through the use of optical and x-ray spectra. Chemical

elements are uniquely identified by the characteristic

frequency of emitted spectra, and amounts present can be

determined by measurement of the intensity of emitted

radiation. However, many factors enter into successful

spectral analysis and must be carefully controlled. These

Include the production of radiant energy by excitation, the

dispersion of the radiant energy into a spectrum, and the

measurement of spectral wavelengths and intensities.

Because of the complexity of the systems involved no way

has yet been found to make absolute measurements of

concentrations in analysis; consequently, comparative

methods are employed in which spectra of unknowns are

measured relative to those of reference materials of known

composition.

The research program of the Section is directed

generally toward a better understanding of the phenomena

Involved in producing and measuring optical and x-ray

emitted energy, and the Improvement of spectrochemical

methods. Instruments, and calibration procedures.

Included in these activities are the development of

standard reference materials, analyses of materials to

assist other research projects, and literature surveys such

as bibliographies and critical reviews.

ill
In this report, the program, facilities, and

accomplishments of the Section for the past year will be

reviewed.

In order to specify the procedures adequately. It has

been necessary occasionally to Identify commercial materials

and equipment In this report. In no case does such Identification Imply recommendation or endorsement by the National

Bureau of Standards, nor does It Imply that the material or

equipment Identified Is necessarily the best available for

the purpose.

Bordon F. Scrlbner, Chief

Spectrochemlcal Analysis Section.

I

iv

I

I
TABLE OF CONTENTS

PAGE

1. PROGRAM AND FACILITIES 1

Program • • • I

Facilities » « 4

2

.

OPTICAL SPECTROMETRY 5

Controlled Atmosphere Arc Excitation •••... 6

Inert Atmosphere Spark Excitation .,o oo*. 8

Arc Temperature Measurements ••• 13

Atomic Absorption Spectrometry 18

Laser Probe Excitation • 21

3. X-RAY SPECTROMETRY 28

Capabilities of X-Ray Fluorescence Spectrometry , p8

Elements that can be analyzed 28

Range of Concentrations Being

Investigated • 29

Precision and Accuracy oo... 29

Modifications of X-Ray Fluorescence Equipment . „ 30

Single -channel Spectrometer 30

Multi-channel Spectrometer 32

Accuracy of Solution X-Ray Spectrometrlc

Ana lysis of Copper Alloys 0. 34

Experlmenta 1 ,, 35

Effect of Film Position 36

Effect of Acid Concentration •.....•• 37

Effect of Temperature o..... ••••••. 37

Analytical Results 37

Discussion 0....0..0 37

Interelement Effects In X-Ray Spectrometrlc

Analysis of Gold Alloys 39

X-Ray Spectrometrlc Analysis of Sliver

Alloys , p , 42

Determination of Coating Thickness 45

4. ELECTRON PROBE MICROANALYSIS 46

Basic Equipment 46

Modifications of the Equipment 49

Program of Investigations o...... 51

Applications ^2
TABLE OF CONTENTS (con't)

PAGE

5. ANALYSIS OF HIGH-PURITY METALS: ENRICHMENT

METHODS 54

Physical Enrichment 54

Analysis of Tin 54

Analysis of Zinc 55

Analysis of Platinum 55

Chemical Enrichment 56

Analysis of Tin 56

Analysis of Platinum 57

6. STANDARDS, ANALYSIS, AND LITERATURE

ACTIVITIES 58

Standard Reference Mate.rials 58

Standards Program 58

Analyses Made of Standard Reference

Materials 59

General Spectrochemical Analyses 62

Types of Analyses 62

General Analyses Made 64

Literature Surveys 64

7

.

PERSONNEL AND ACTIVITIES 65

Personnel Listing 65

Publications 66

Talks Given 69

Committee Activities 71

8. ACKNOWLEDGMENTS 73

9

.

LIST OF REFERENCES 74

vi
LIST OF FIGURES

FIGURE NO. PAGE

1. Design of an arc sheath for excitation in

controlled atmospheres 7

2. Device used for atmosphere control in inertgas spark excitation 10

3. Calibration curves for the determination

of nickel in high-temperature and ferrous

alloys in argon atmosphere 12

4. Diagram of cross -section through an arc

column, indicating contributions from

four zones to intensities measured along

four lines of sight I5

5. Results of a set of measurements of temperatures in a 20-amp. d.-c. arc in argon .... I7

6. Calibration curves for atomic absorption

spectrometry, for the Fe resonance

line at 2522. 85A 21

7. Optical diagram of the laser probe 22

8. The laser probe in position on a

spectrograph 23

9. Calibration curves for the determination

of Cr, Si, and Mn in low-alloy steel

with the laser probe 26

10. Single -channel x-ray fluorescence

spectrometer 3I

11. Multi-channel x-ray fluorescence

spectrometer 33

12. Apparatus to measure the position of

the film 36

13. Calibration curve for gold in gold alloys,

linear case 39

14. Analytical curve for gold in gold alloys,

non-linear case, uncorrected 4l

vii
LIST OF FIGURES (con»t)

FIGURE NO. PAGE

15. Comparison of gold detenalnations by chemical

%ftd x-ray methods. X-ray results corrected

by the Luca^-Tooth^ Me th©d= i . i ..,%%»»%*%».. . 4l

16. Linear calibration curve for copper in

silver alloys 43

17. Non-linear calibration curve for tin in

silver alloys 44

18. Corrected calibration curve for tin in

silver alloys 44

19. Electron and x-ray scanning images 47

20. Electron probe microanalyzer 48

21. Chromium (a) and aluminum (B) x-ray scans

of a cracked segment of a t\irboprop

inlet guide vane 53

22. Direct reading spectrometer with

automatic read-out system 60

23. Multi-channel optical spectrometer 6I

24. Optical spectrograph, 3.4-meter Ebert .... 63

LIST OF TABLES

TABLE NO. PAGE

1. Matrix element composition of some NBS

Standard Reference Materials 9

2. High-voltage spark parameters 11

3. Variability of line intensities for

laser probe excitation 25

4. X-ray spectrometer settings 36

5. Comparison of chemical and x-ray results ... 38

viil
SPECTROCHEMICAL ANALYSIS: OPTICAL SPECTROMETRY X-RAY

FLUORESCENCE SPECTROMETRY, AND ELECTRON PROBE

MICROANALYSIS TECHNIQUES

July 1964 to June 196

Edited by Bourdon F. Scrlbner

ABSTRACT

A summary is given of the activities of the Spectrochemical Analysis Section for the period from July, 1964

through June, 1965. Activities in optical spectrometry

included studies of excitation by arcs and sparks in

controlled atmospheres and by the laser probe, the measurement of arc temperatures, and atomic absorption spectrometry

In x-ray spectrometry, methods have been developed for the

analysis of copper alloys in solution, as well as silverbase, and gold -base dental alloys. An electron probe microanalyzer has been installed, and a description is given of

the modifications that have been made to the instrument, the

plans for future investigations, and some applications.

Chemical and physical enrichment methods have been developed

for the analysis of high-purity tin, zinc, and platinum.

Homogeneity tests and analyses have been performed in the

development of standard reference materials. Other activities included analyses of samples to assist other NBS groups

and government agencies, and literature surveys. Listings

are given of 20 publications and l4 talks by members of the

Section within the year.

ix

1. PROGRAM AND FACILITIES

A. Program

The Section is organized into several groups of which

two are concerned with research and analysis in broad

spec trome trie fields, one on optical spectrometry and the

other on x-ray spectrometry, including electron probe

microanalysis. Other groups are concerned with problems

across both of these fields: the development of enrichment

methods for increased sensitivity; the investigation of

problems of calibration; analyses of materials; and

literature reference surveys. All groups are involved in

the development and analysis of appropriate standard

reference materials.

In optical spectrometry major attention is being

given to the study of phenomena in the excitation of atomic

spectra and the application of this information to the

design of new or improved excitation sources. Excitation is

a prime problem in optical spectrometry and advances in

this field can be expected to stem from the development of

excitation sources of steady characteristics, better line

to background Intensities, or broader applicability.

The marked effects of the gaseous atmosphere around the

arc or spark column on the characteristics of the discharge

have become evident in recent years and we have an active

program in this field. Our study of this problem has

involved in one instance the development of a simple means

for providing a streamlined flow of a gas mixture around an

arc, resulting in a convenient and effective way of

controlling the gaseous medium for excitation. The source

provides a steadier arc and produces spectra freer of

interfering molecular bands. Another area of investigation

concerns the effects of the gaseous atmosphere on spark

excitation. Here the use of an inert atmosphere with

elimination of oxidation effects promises to reduce interelement effects in the analysis of complex alloys, A

device for shielding the spark in a stream of gas was

devised and conditions were found which effectively

eliminate interelement effects in the analysis of hightemperature alloys. This work is of considerable

II
Importance In our general effort toward minimizing the

number of standard reference materials for calibration

in the analysis of alloys.

Another study under way is an examination of the

phenomena involved in arc excitation to provide a better

basis for explaining and predicting the excitation behavior

of complex mixtures. One of the more important parameters

for excitation is the temperature of the source, and

measurement of arc temperature and its effect is under way.

The development of the laser with its high momentary

energies offers an intriguing possibility for vaporization

of materials for spectral excitation. Our study of this

problem has been in the direction of a better understanding

of the factors controlling the reproducibility of laser

pulses, and of the characteristics of this source for

quantitative analysis.

Atomic absorption spectrometry is recognized as one of

the important means of measuring concentrations of atoms

and promises to supplant flame photometry in many cases.

Our effort here is directed toward improving the production

of the atomic species and the quantitative measurement of

concentration. An investigation of simultaneous measurements of several elements using a continuum source is

nearing completion.

In x-ray spectrometry the program involves activity in

x-ray fluorescence spectrometry and in electron probe microanalysis. Improved analytical methods have been developed

for the x-ray fluorescence analysis of gold alloys, silver

alloys, and copper alloys. Increased attention is now

being given to the problem of interelement effects and their

correction in order to improve the accuracy of analysis.

The instrumentation for this work is being studied

critically and modifications of equipment are being made to

improve precision of measurement and to extend the method

to the determination of the lighter elements.

The electron probe microanalyzer is one of the most

versatile tools for analysis that has been developed. Not

only can elements in microscopic areas be identified but

quantitative analysis can be made and the distribution of

elements observed over selected areas. During this year

2
much effort was expended In the installation and

modification of an electron probe microanalyzer . It is

operating successfully and has been applied to several

analytical problems. A beginning has been made in studies

of certain fundamental factors that aXfect the sensitivity

and accuracy of analytical measurements with the microprobe. Immediate attention is being given to the use of

specimen current measurements for quantitative analysis,

to studies of coincidence loss correction for the detector,

and of pulse height variation as a function of counting

rate, A general program of research has been planned in

this field as discussed later in this report.

The analysis of high-purity metals is one of the

critical problems for modern science and technology.

Spectrometric methods are useful for trace analysis but

the high level of purity now being obtained for some metals

has pushed direct methods to the limit in detection of

impurities. However, concentration of the impurities by

physical or chemical separations offers a means of reaching

the required sensitivities. These possibilities are being

investigated and a fractional distillation method in arc

excitation has been found useful for survey analysis of

pure metals.

The analysis activities involve the study of

calibration problems and the application of methods of

analysis to real samples. These include the study of

homogeneity of materials intended for standard reference

materials, the analysis of the selected standard reference

materials by primary methods, the analysis of materials for

other research groups, and the survey of literature to

maintain up-to-date reference files and to prepare

bibliographies and reviews for publication.

The personnel of the Section this year totalled ten

full time and five part time employees with assignments to

areas of activity as given in the personnel listing. In

addition, the facilities of the Section are made available

on occasion to responsible investigators from outside.

Four individuals who spent an appreciable length of time as

guest workers in x-ray spectrometry are indicated in the

listing.
B. FaclXltles

The Section is located In. the NBa Chemistry Building

on the ground floor, a circumstance which has proven

advantageous for the mounting of vibration-sensitive

optical equipment. The laboratories consist of several

spectrometer rooms In which temperature and humidity are

controlled to 75°±1F and 405^±5 RH, two general-purpose

chemistry laboratories, a dark room, a sample preparation

room, and the Section Office, Electrical facilities Include

heavy-duty single and three-phase a-c power, d-c power,

trunk line connection to the Power House for special power

needs, and standard frequency service lines. Ventilation

Is provided by fresh air Intakes through blowers, and by an

exhaust system largely through exhaust stacks over arc or

spark excitation sources and through chemical hoods.

The equipment available to the Section provides unique

facilities for the observation of spectral wavelengths and

measurement of radiated energies In optical emission and xray spectrometry. The optical Instrumentation Includes

high-resolution grating spectrographs, multi-channel

photoelectric spectrometers, a single channel scanning

optical spectrometer, and comparator-mlcrophotometers for

measuring spectrograms. The basic x-ray equipment consists

of a single channel spectrometer, a multi-channel

spectrometer, and an electron probe mlcroanalyzer recently

Installed.

The large spectrometers are required mainly to provide

high speed and high precision In the spectrochemlcal

analysis of standard reference materials especially for

homogeneity testing; their cost has been Included In the

fees for these materials.

Much attention is being given to up-dating the

equipment of the Section in view of marked advances in

electronic circuitry and also in anticipation of the move to

the new NBS site at Gaithersburg, Some of this

modernization has been completed, notably for the multichannel x-ray spectrometer.

Details on the instruments, their modification, and

applications 'are given in the appropriate sections of this

report,

4
2. OPTICAL SPECTROMETRY

A major interest of this Section in research in

optical spectroscopy has been the development of new or

improved excitation sources and the study of the properties

of existing sources. Atomic spectra can be excited in many

ways; any method that produces a high enough temperature to

convert a solid or liquid sample into an atomic vapor will

usually also provide energy to excite some of the atoms to

emit light. Naturally, not all of these sources will have

equally desirable properties in terms of the type of spectra

excited and the convenience of operation. Certain electrical discharges have been found to have particular utility

for spectrochemical analysis, and d-c and a-c arcs and highand low-voltage sparks have been widely employed for this

purpose because of their convenience and general

applicability. Flame excitation has also been employed

since the earliest days of atomic spectroscopy, but its

use is largely restricted to those elements with low

excitation energies.

These common excitation sources are satisfactory for

the majority of analyses, but they are not always applicable

to special problems. It is often necessary to develop new

or improved sources to meet particular requirements, such

as improved sensitivity, accuracy, or precision; for the

determination of the few elements which are not excited in

the usual sources; or to analyze samples which are limited

in quantity or which have unusual forms. To obtain the

best possible analytical results with either old or new

sources, it is important to understand the mechanisms by

which the samples are vaporized and excited and the

influences of changes in the experimental parameters[l]

Until recently, all spectrochemical analyses were

based on emission spectra. Observations of atomic absorption spectra have long been employed in astrophysics and

some areas of atomic physics, but such observations were

not applied to analyses in the laboratory. Atomic

absorption spectroscopy has developed rapidly as an

analytical method in the past decade. This new technique

offers certain advantages, but, as with any new method, it

has a number of difficulties which must be defined and,

if possible, eliminated.
A. Controlled -Atmosphere Arc Excitation

In spectrochemlcal analysis. It Is the normal practice

to excite the samples In an electrical discharge In air. |

This Is primarily a matter of convenience; although

replacement of air around the arc with other gases Is known

to produce some benefits, the use of controlled -atmosphere

excitation has been limited by the practical difficulties

involved.

The most obvious advantage of controlled -atmosphere arc

excitation is the elimination of CN bands (CN is formed by

reaction of the graphite electrodes with nitrogen in the

air) which obscure the most sensitive lines of several

elements. In addition, the temperature of the electrodes

can be reduced by burning the arc in argon or helium,

rather than in air or some other reactive gas, since a considerable portion of the heat generated at the electrodes

comes from reactions of the carbon with the gases. By

reducing the temperature of the electrodes, it is possible

in some cases to vaporize volatile impurities while leaving

the more refractory matrix behind. Excitation in an active

gas may sometimes be desirable; for example, if the sample

is excited in chlorine, those elements forming volatile

chlorides should be selectively vaporized. The atmosphere

aroxind the arc also produces other effects, related to

changes in the temperature, electron density, and chemical

reactions in the arc, but these are poorly understood at

present.

Although the effects of controlled atmospheres have

been applied in spectrographlc analysis, it has until

recently been necessary to enclose the samples in a chamber

for this purpose. The use of a chamber introduces

practical difficulties, including delays in changing ; electrodes between samples, the need for flushing the

chamber before excitation can be started, and clouding of

chamber windows by deposits of sample and electrode vapors.

It has recently been shown that samples can be vaporized

and excited in arcs in controlled atmospheres by

surrounding the electrodes and the analytical gap with a flow of gas, thus eliminating the need for a chamber. The

devices which have been described for this purpose all had

one or more disadvantages. Either they did not adequately
exclude air, or they required extensive modification of

the arc stand, or they did not provide for rapid change

of electrodes.

Devices have been developed in the Spectrochemlcal

Analysis Section [2] which make it possible to excite

samples as rapidly and conveniently in controlled

atmospheres as in air, which do not require modification

of the arc stand, and which can be put in place or removed

easily. One of -these is shown in figure 1, It is made of

Figure 1. Design of an arc sheath

for excitation in controlled atmospheres.

copper, except for the threaded electrode holder, which is

stainless steel. The extension rod on the bottom, diameter

i in., fits into the lower Jaws of the arc stand. The gas

or gas mixture is introduced at the bottom of the chamber,

passes through a pierced plate, and flows around the lower
electrode to sheathe the arc. The taper of the chamber has

been found to be necessary to give adequate exclusion of

air. The top of the chamber is water cooled to prevent

damage by the heat of the arc. The electrode holder is

threaded to permit positioning of the electrode before

excitation is started.

The device has been used with gas flows of 5 or 10

1/min, the lower flow providing less complete exclusion of

air as shown by the appearance of CN bands in the spectrum.

No flushing is needed once the system has been purged of

air, and the arc may be ignited within a few seconds after

the gas flow has been started. Thus, the system conserves

gas.

An additional advantage of the device, compared to

excitation in air or in a chamber, is that the concentric

flow of gas around the arc stabilizes the position of the

discharge, presumably by overcoming the convection currents

which ordinarily cause the arc to wander.

This device and others similar in design but differing

slightly in construction have been used in a number of

analyses. It has also been employed in a study of the gross

effects on the spectra of changing the atmosphere around the

arc. The observations have been in good agreement with

published data obtained with arcs in sealed chambers. The

device is also being used in measurements of arc temperatures in various atmospheres (see below).

(M. Margoshes and B. F. Scribner)

B. Inert Atmosphere Spark Excitation

Quantitative spectrochemical analysis is a comparative

method. It is not now possible to calculate the relation

between element concentration and line intensity, which must

be determined by recording the spectra of standards of known

composition which are excited in the same way as the samples.

The line intensities depend not only on the concentration of

the analyte in the sample and the method of excitation and

recording of the spectra, but they are also affected by

other elements which are present and by the physical form of

the sample. For this reason, it is necessary that the

standards be as similar as possible to the samples which are

to be analyzed.

8
Point- to-plane spark excitation Is a rapid method for

the analysis of metallic samples, since this technique

requires a minimum of sample preparation and provides

adequate sensitivity and precision for most purposes.

However, standards for this method of excitation are

difficult to prepare. The analysis of high- temperature

alloys has presented especially severe problems In

standardization for polnt-to-plane spark excitation.

The major constituents of high- temperature alloys may

be Iron, nickel, or cobalt, or a combination of the three,

and chromium Is also a common major element. Table 1 lists

Table 1. Matrix element composition of some NBS

Standard Reference Materials.

Concentration ^

NBS No. Cr Nl Fe Co

1184 19.44 9.47 ^ > •B ^ 1185 17.09 13.18 ... 1186 16,60 24.50 50.7 0.05^

1187 21.62 20.26 27.4 20.80

1188 15.40 72.65 6.60 —

1189 20.30 72.60 1.40 0.06

1190 17.00 51.9 0.6^ 19.1

1191 19.48 55.15 2.04 13.65

1192 17.88 57.25 1.58 11.40

1203 11.90 75.5 1.4a —

1204 12.75 70.6 3.1^ ._ 1205 13.82 67.5 1.55^ —

b

a. Values not certified.

the contents of some elements in high- temperature alloy

standards presently supplied by NBS for calibration of

emission and x-ray spectrometers. This variety of matrices,

plus wide differences in the chemical and metallurgical

properties among the various alloys has required close

matching of specimen and standard for accurate spectrochemical analysis. With more than 200 high- temperature

alloys in use [3], it has become prohibitive to have

closely matching primary standards available for all alloys.

9
Instead, we have chosen to develop methods which would make

a smaller number of standards applicable to the analysis of

a variety of alloys.

In recent years several papers have been published

describing the use of controlled atmospheres in point-toplane spark analysis of alloys. In particular, Arrak(4] , using either argon or nitrogen atmospheres, was able to fit

several types of ferrous-base alloys to a common set of

analytical curves. The present work [5] was undertaken in

order to extend this method to the analysis of hightemperature alloys,

Controlled-atmosphere excitation has ordinarily been

done by means of air-tight chambers enclosing the sample and

counter-electrode. Use of a chamber sacrifices speed of

analysis, one of the important characteristics of emission

spectroscopy, since considerable time is required to change

samples and replace the air in the chamber with the desired

atmosphere. In the present work, the device shown in

figure 2 was employed to introduce argon or nitrogen into

Figure 2, Device used for atmosphere

control in inert-gas spark excitation.

10
the gap and to force the gas to envelop the counterelectrode, excitation column, and excited area of the

specimen. The gas Is Introduced around the counterelectrode at a flow of 6 1/mln. Both the sample and counterelectrode can be changed as rapidly as in normal operation

In air, and excitation can be started as soon as they are

in place. Two spectrometers were used in this work, and

the high-voltage spark parameters are listed for these two

instruments in table 2. With these parameters there is a

Table 2. High-voltage spark parameters.

Instrument A Instrument B

Discharges per cycle

Inductance, iih

Capacitance, \if

R,-f, current, amps

Primary resistance, ohms

Counter electrode

Analytical gap, mm

4

90

0.007

6

residual

2

36

0.00725

11.5

34

J- in, graphite, hemispherical

tip, *ASTM Type C-5

2.5 2.5

transfer of graphite from the counter electrode to the sample

surface. The role of the graphite is not known, but the

electrical conditions giving the desired results have always

caused a deposit of graphite on the sample.

Figure 3 shows calibration curves for the determination

of nickel in high- temperature and ferrous alloys by this

method. With excitation in air the points would be

scattered, and it would not be possible to fit them to a common curve. Because no element is present at a nearly

constant concentration it was necessary to plot calibration

curves in terms of the concentration ratio. Good results

were obtained with both argon and nitrogen atmospheres, but

in some cases the scatter of the points was somewhat poorer

in nitrogen. Self -absorption was less significant in either

argon or nitrogen than in air, with argon again giving

better results. In argon, a linear calibration curve could

be obtained for the determination of nickel in the range

from 9 to 705^, using the most sensitive resonance line of

this element, without self-absorption being evident. The

11
.6 2.4

READOUT (seconds)

Figure 3. Calibration curves for the determination

of nickel in high- temperature and ferrous

alloys in argon atmosphere.

background intensity was nearly constant, regardless of the

sample, in either argon or nitrogen, while in air the background varied markedly from one alloy to the next. The

background was lower in nitrogen than in argon, making the

former gas more satisfactory for determination of smaller

element concentrations.

With excitation in air, the emission intensities do

not become constant with time until an equilibrium has been

established between the composition of the specimen, of the

12
surface being sampled, and of the vapor. It is ordinarily

necessary, for this reason, to pre-spark the sample for a period of time ranging from a few seconds to as much as a minute or more in extreme cases before the exposure is

started. Once equilibrium has been established, there is

only an indirect relation between the composition of the

specimen and of the vapor, and line intensities do not

necessarily increase in proportion to the content of the

element in the sample. In argon or nitrogen atmospheres it

has not been found to be necessary to pre-spark the samples.

The line intensities reach a steady value virtually as soon

as the spark is started. In addition, line intensities are

more nearly proportional to concentration.

It seems likely that the observed effects of the

controlled atmosphere are due to the fact that the specimen

surface does not become oxidized under these excitation

conditions. However, it is possible that one effect of the

inert atmosphere is to prevent oxide formation in the vapor.

More experimental work is needed to define the mechanism of

the matrix effect and how it is overcome by controlledatmosphere excitation. However, the methods which have been

developed provide an effective means for reducing the number

of primary standards needed for initial calibration in

spectrochemical analysis of high- temperature alloys.

(H. C. Dilworth and M. Margoshes)

Co Arc Temperature Measurements

The most important single physical parameter of an

excitation source is its temperature. At thermal

equilibrium, the population of excited states of an atom or

ion is exponentially proportional to the temperature. The

degree of ionization of an element is governed by the Saha

equilibrium which contains the temperature in both an

exponential term and a term in T-^^ . Little is known about

chemical reactions in arc or spark plasmas, other than the

fact that chemical compounds are present, as shown by the

appearance of some band spectra, but the temperature of the

source must be one factor affecting the extent of such

reactions.

13
There have "been a number of measurements of arc and

spark temperatures in air, but the results obtained bydifferent investigators are not* in good' agreement. This is

partly because these studies have not taken into account

the distribution of temperature through the discharge, but

have assumed that the plasma could be characterized by a single temperature. In fact, the discharges are generally

hotter on the axis than at the periphery, and there are also

different temperatures near the electrodes than at the

center of the gap. The temperatures measured are usually

an average of the temperatures of the different portions of

the plasma. This average value will be different depending

on how the temperature is measured. For example, there will

be considerably more ionization in the hotter portions of

the discharge, so temperatures measured from the relative

intensities of lines of ions will be higher than those

measured from lines of neutral atoms.

The intensity, I, of an emission line under conditions

of thermal equilibrium is given by

I = KCgf/A^)e-^/^^' (1)

where K includes several constants as well as a term for

the number of atoms or ions of the emitting element, gf is

an atomic constant for a particular emission line, E is the

energy of the excited state of the line, k is Boltzman's

constant, and T is the temperature. Eqn. (l) may be rewritten in logarithmic form and rearranged to give

logClA?/gf)= log K - 0.4343E/kT. (2)

Thus, if the left-hand side of the equation is plotted

against E for a number of emission lines of a particular

atom or ion, the points should lie along a straight line

whose slope is inversely proportional to the temperature.

In order to take into account the distribution of

temperatures in the source, it is necessary to measure the

line intensities emitted separately in the different

portions of the plasma. However, these intensities cannot

i

I

14
be measured directly. Figure 4 shows a diagram of the

^lA=aI., ^ lB=a'l| + b'l2

Ic=a"l,+ b'Vc"l3 ^ lD=a"'l,+b"'l2+c"'l3+d'"l4

T^>T3>T2>T,

Figure 4. Diagram of cross-section through an arc

column. Indicating contributions from four

zones to Intensities measured along four

lines of sight.

cross-section through an arc plasma. It is here considered

to be made up of 4 concentric zones, each characterized byconstant properties but with the temperature increasing from

zone 1 to zone 4, The Intensity, I., measured along lineof-sight A is a function of the line intensity emitted per

unit of volume in zone 1 and of geometric factors. The

intensity, Ig, viewed along line-of-slght B is given by the

intensities emitted per unit volume in zones 1 and 2 and the

appropriate geometric factors. The intensity per unit

volume as a function of radius, I^, can be determined from

the Intensity per unit volume as a function of the projected

distance along the arc image, I , by the Abel inversion:

15
where r is the radial distance from the axis of the

discharge, r^ Is the maximum radius, and x Is the distance

from the center along the projected arc Image.

Measurement of I^ requires that the source be stable

In time and space for the Interval needed to record the

spectra. Measurements with the spark, which changes

rapidly with time, require time-resolution of about a microsecond. Arcs do not change rapidly with time, but they

ordinarily have a tendency to wander, which makes the

observations difficult. However, it is possible to

stabilize an arc, and at the same time to control the

atmosphere around the discharge, by means of the gas sheath

described earlier (see above ).

Studies are now under way to determine arc temperature

distributions in atmospheres of air, argon, and argon-oxygen

mixtures. These atmospheres were selected because they are

the ones most commonly used in spectrochemical analysis and

because there is evidence that arcs in these atmospheres

are in thermal equilibrium. In contrast, an arc in a helium atmosphere, which is also sometimes used for spectrochemical analysis, is apparently not in thermal equilibrixim.-

The temperature of a discharge is a function of all

components of the plasma. Including the elements in the

sample, so the measurements will be made with a niomber of

elements in the electrodes.

In the first experiment, the arc was operated at 10

amps in an atmosphere of argon and with titanium in the

lower electrode — the anode. The image of the arc was

rotated 90° by a mirror system and focused onto the slit of

the spectrograph, so that the light passed by the slit was

a cross i-sectlon through the plasma at a point 2 mm above

the anode, with a total arc gap of 6 mm. The values of I^

were then determined by measuring points along the line

Images on the photographic emulsion. The image was

magnified 3.5X to permit the I^^ measurements to be spaced

more closely; approximately 15 measurements could be made

across the image of each line,

16
A group of ten Tl II lines with known gf -values

were measured, and the Abel inversion was done by means of

a computer. ' Plots were then made of log (lA^/gf ) vs. E

for these lines at a number of radial distances, the slope

of each line found by a least-squares fit to the data, and

the temperatures determined from the slopes. Figure 5

5800 —

5400 —

o

uT

3

h-<

Q- 5000 -

UJ

4600 -2-1 I 2

RADIAL DISTANCE FROM AXIS, MM.

Figure 5. Results of a set of measurements of temperatures in a 20-amp d-c arc in argon.

shows the results of the first measurement. The arc was

found to have a temperature of 5800° K at the center, with

little change over a radius of I'l to 2 mm but dropping

sharply at larger radii. The difference between the

17
temperatures at equal radii on either side of the

center is within experimental error.

Now that a method has been established for the

determination of arc temperatures as a function of position

in the discharge, it should be possible to make detailed

studies of the effect of the atmosphere, the sample, and the

arc current on this important parameter. Knowledge of these

values should make it possible to interpret the effects of

these operating conditions on observed emission intensities,

and to make a more rational choice of operating conditions

for a particular analysis.

(M. Margoshes and H. E. Bond)

D, Atomic Absorption Spectrometry

Atomic absorption spectrometry is a relatively new

method of analysis, based on the absorption of characteristic ultraviolet or visible radiation (usually the resonance

lines) by atoms. In the normal mode of operation, light

from a hollow cathode source passes through a chopper and a flame into a spectrometer, which is set to measure the

intensity of one line of the analyte. The sample, in the

form of a solution, is sprayed into the flame where it

volatilizes to give a concentration of free atoms in the

flame which is proportional to the element concentration in

the solution. These free atoms absorb a fraction of the

characteristic radiation, and the absorbance of the flame is

related to the analyte concentration by suitable standards.

Atomic absorption spectrometry has been shown to

provide good sensitivity of detection for a number of

elements. The equipment is moderate in cost, and analyses

can be done rapidly (once the sample is in solution) and

with reasonable precision. Because a flame is used to

convert the sample into atomic vapor, atomic absorption

spectrometry is subject to many of the same interferences

as is flame photometry, including disturbances in sample

feed rate, shifts in ionization equilibria, and formation

of stable chemical compounds in the flame. On the other

hand, atomic absorption spectrometry is often more specific

than is flame photometry. The resolution achieved is

determined by the band-width of the emission line in the

18
hollow-cathode lamp, not "by the spectrometer, so other

elements In the sample are not detected. In fact, it is

possible to do isotopic analyses by employing a single

isotope in the hollow-cathode lamp. Such analyses h^ave

already been done for Li and U.

One presently limiting factor in atomic absorption

spectrometry is that it has not been possible to use the

same hollow cathode source for the determination of several

elements in a sample. The lamps are expensive and have a limited life, and a stock must be kept on hand for the

analysis of all elements of interest. The lamp must be

changed for the determination of each new element, and it

must be warmed for about I5 minutes to reach steady intensity. Recently, lamps have- been built containing three or

four "compatible" elements, but there are severe limits on

which elements may be combined in a single lamp.

Atomic absorption spectrometry with a continuum source,

together with a spectrometer equipped to measure the

intensities of several lines either simultaneously or in

rapid sequence, would seem to offer promise as means of determining a group of elements in the same sample. The

absorption lines in the flame are quite narrow — much

narrower than the resolution limit of all but the largest

spectrographs — so there will be some loss of sensitivity

and specificity compared to the high effective resolution

attained by using a hollow cathode lamp. However, for

many purposes the losses will be more than compensated by

gains in speed of analysis and by the convenience of not

having to stock a large numbier of lamps.

Our first efforts in this direction, in 1962, were with

a tungsten filament lamp. Absorption spectra were detected

for several elements, including Na, Sr, and Ca . However,

the sensitive lines of most elements are in the ultraviolet,

where the tungsten lamp emits little or no light. Some

efforts were made at that time with a high-pressure xenon

lamp as a source, but the lamps then available were

extremely unstable, although they did emit copious ultraviolet radiation. A more stable high-pressure xenonmercury lamp has since become available, and work has

resumed with this source,

19
An instrument originally designed for emission

spectroscopy has been modified for use as an atomic 1 absorption spectrometer. The. heart of the spectrometer is i a 3A-ni Fastie-Ebert spectrometer equipped with a 1200 ' groove/mm grating and a photomultiplier detector. With | entrance and exit slit widths of 10 microns, the measured

resolution is about 0.2 A in the first order. The

instrument is equipped with a chopper and a phase-sensitive i a-c amplifier, A quartz plate in front of the slit reflects { a fraction of the undispersed radiation onto a second j photomultiplier, and the line intensity can be measured, if

desired, as a ratio to the undispersed radiation.

] A notable characteristic of the instrument for the \ present purpose is its capability of measuring the

intensities of up to 12 lines in rapid sequence, at 6 sec/ j line. A mechanical system, which is fairly easily adjusted i to select the lines of interest, positions the rotation of

the grating to select the approximate wavelengths of

' interest. The instr\iment steps to these positions in \ sequence and at each point it scans a narrow wavelength { ; region which includes the peak of the line. Individual j sensitivity controls are provided for each of the 12 wavelengths which can be measured.

Figure 6 shows calibration curves for the Fe 2522A

line obtained with this instrument with a hollow-cathode

lamp and the high-pressure Xe-Hg lamp as the source. There

is some loss of sensitivity and curvature of the calibration

curve with the continuum source, as is to be expected.

These effects are caused by the limited resolution of the

spectrometer compared to the true width of the absorption ^ line. Under these conditions, it cannot be expected that

the curves will follow Beer's law. Some improvement in

sensitivity results when measurements are made at higher

resolution by using the grating in the second order.

Studies are now under way to define the precision of

atomic absorption analysis with the continuum source as

compared to hollow cathode sources, and to test the method

in the rapid sequential determination of several elements

in an alloy, including the matrix element, alloying elements,

and impurities.

(M. Margoshes ancj M. M. Darr)

20
0.4-

0.3-

UJo

z

<

03

q:o

CO

CD<

0.2-

0510 20

RP.M.

Figure 6« Calibration curves for atomic

absorption spectrometry, for

the Fe resonance line at 2522. 85A.

o- with hollow-cathode lamp; •- with high-pressure Xe-Hg

lamp, grating used in first order;

D ^ with high-pressure Xe-Hg

lamp, grating used in second order.

E. Laser Probe Excitation

In June, 1963, we began the task of determining the

characteristics of a laser probe [6] for qualitative

and quantitative analysis of samples as small as 35 M- in

diameter and 20 M- thick. From the beginning, there have

been three parts to this task:

1. To experimentally investigate the characteristics

of spectra produced by the laser probe for a wide variety

of Instrument parameters and specimen conditions, the direct

object of these experiments being to correct any defects in

the design of the prototype instrument and to define techniques for carrying out several specific types of analyses.

21
2. To define the areas where the laser probe can be

of most use as an analytical tool,

3. To define the changes in instrumentation and

technique needed to make the laser probe adaptable to

analyses it cannot already do, e.g., quantitative analysis

of a single microspecimen of unknown type.

Four specific features of the laser probe make it

particularly attractive as an analytical tool. It consumes

a small amount of sample per analysis — about 0,1 [ig.

Under usual circumstances, there is no need for surface

preparation, which might cause contamination. The method

has high absolute sensitivity for those elements considered

as sensitive spectrochemically; amounts as small as 10 pg

have been determined for some elements. Furthermore, the

specimen need not be electrically conductive.

The design of the laser probe is shown in figure 7.

i

FLASHLAMP

557o

REFLECTOR45* y, ^

PRISM Xl "0---

EYEPIECE

REFLECTOR

ROTATING PRISM

{Q SWITCH)

/

RUBY ROD

VIEWING MIRROR

MICROSCOPE OBJECTIVE

SPARK ELECTRODES

SAMPLE

Figure 7. Optical diagram of the

laser probe.

I

A photograph of the instrument in position on a spectrograph

is shown in figure 8. A Q-switched ruby laser provides the

energy for vaporizing the sample. The 69^3 A laser light is

focused onto the specimen by a metallurgical microscope which

Is also used for specimen viewing and sample area selection.

22

i
Figure 8. Laser probe in position on spectrograph: Left:

Electronics cabinet containing power supply and

controls for laser head and cross-excltatlon

spark; Top center: Silt -end of 21 -ft Wadsworth

mount grating spectrograph; Top right: Laser

probe, consisting of laser head and microscope;

Lower right: Arc -spark power supply (not used

with laser probe).

The measured power at the peak of the laser pulse, approximately 4 X 10° watts, is sufficient to vaporize any material

present at the focal point. Typical sample pits in steel are

4o to 50 \i in diameter and about 20 M- deep, corresponding to

a sample weight of about 10"'^ g. Additional energy for exciting the sample vapor is provided by a spark circuit, with

23
adjustable voltage, capacitance, inductance, and resistance,

connected to graphite electrodes placed Just above the specimen. The partially-ionized vapor passes between the charged

electrodes, automatically triggering the spark.

Because of the very small amount of sample consumed,

the spectra are weaker than in most spectrographic analyses.

A critical examination of spectrograph illumination v/as necessary to insure that the light from the source is used as

efficiently as possible. For quantitative analyses, a pair

of crossed cyclindrical lenses was used to illuminate the

slit evenly with a minimum loss of light. For qualitative

analyses, spectra about 4 times as bright are obtained by

focusing the spark onto the slit with a spherical lens.

Other efforts to Improve the instrument for laser-probe

analyses included investigation of optical component failures

due to the high radiant flux of the laser beam, temperature

control of the laser ruby rod, control of voltage to the

flash-lamp used to pump the laser, and mechanical changes to

permit easier optical alighment of the source with the

spectrograph.

The characteristics of the spectra produced without the

electrical spark have also been determined [7]. In general,

when not sparked, the vapor cloud formed by the laser pulse

which are weaker in intensity than the sparked spectra by a factor of 10 to 15 . Although the laser without the spark

has been suggested as an analytical tool, most of our

studies have been carried out with spark cross-excitation,

the laser being used primarily as a sampling device.

Vvhen the laser is considered as a sampling device, it

is possible that the over-all intensity of a spectrum and

the relative intensities of lines in the spectrum will be

controlled primarily by the amount and rate of introduction

of the sample into the spark. A considerable variation in

the spectrum from one exposure to the next, even with the

same homogeneous specimen, would be expected if the laser

output varied and thereby changed the sampling process.

Such variations were observed early in this study.

An apparatus was designed to monitor the laser output

vs. time, recording the event on a high-speed oscilloscope

[ 8 ]. When the laser output was initially checked with this

system, it was found to consist of 2 to 10 or more spikes

24
and to be quite unreproducible from one pulse to the next.

'The variation of the total energy of a pulse was as large as

-50^. Using the output monitor, the laser output was Investigated as a fxanctlon of the energy supplied to the flashlamp which pumps the laser, the temperature of the ruby-rod,

and the optical alignment of the cavity. Parameters were

determined which yielded a single -spike output with the peak

power and the energy of the pulse reproducible to about -10^

[9], The Improved control of the energy of the slngle-splke

pulse gives a visible Improvement In the reproducibility of

the size of the sample pits, compared to multiple -spike

operation. However, because of the Irregular shape of the

pits. It has not yet been possible to measure sample volumes.

The effect of Improved sampling reproducibility was

Investigated by comparing the variabilities In spectrum line

Intensities produced by slngle-splke and 4-splke laser

operation. Table 3 shows the results of this experiment.

Table 3. Variability of line Intensities

for laser probe excitation (sample

size =12).

A. Coefficients of variation, ^, for line

Intensities.

4 spikes

1 spike

Mn II 2576

19

9

Ni I 34l4

39

11

Cu I 3273

38

15

B. Coefficients of variation, %, for intensity

ratios.

4 spikes

1 spike

Mn 2376

Fe 292b

10

9

Nl 3^14

Fe 292b

18

12

Cu 3273

Fe 292b

14

15

25
In addition, analytical curves have been established for

single- and 4-spike operation using NBS standards of lowalloy steels^ high -temperature alloys, and zinc -base diecasting alloys. A representative set of analytical curves

is shown in figure 9.

<

>•H

^ 0.5

UJH

Z

0.2

]—I I I I

I 1

\

\—\—I I I I

NBS LOW-ALLOY STEEL STANDARDS

Cr3593/Fe2926

Mn2933/Fe2926 _

'Si288l/Fe3440

4 SPIKES, 4 SUPERIMPOSED SHOTS,

AV. OF 3 SETS i I STD. DEV.

I I I I I I

I I I I I I I

I

005 0.1 0.2 0.5

CONCENTRATION -7o

Figure 9. Calibration curves for the

determination of Or, Si, and Mn

in low-alloy steel with the

laser probe.

The laser probe has been successfully applied to

several qualitative analytical problems, including:

Identification of a surface stain and metallic

particles on a ceramic disk. For identification of the

stain, the laser beam was defocused in order to form a pit

60 V- in diameter and only 10 I-l deep.

Identification of the material of a wire 75 M- in diameter,

26
Qualitative analysis of individual grains, 40 to 50

in diameter, of silver-alloy powders of the type used in

making denta-l amalgams. For these analyses, the grains

were mounted on an adhesive tape.

Qualitative analysis of the components of a semiconductor micro-diode. The main portion of the diode was

1 X ^ X ^ mm, the lead wires were ^ mm wide, and the active

head was 0.4 mm x 0.2 mm.

The future program includes investigating Q-switching

methods employing a saturable absorber in an attempt to

increase the power output in a single spike. If successful,

this would make it possible to vaporize a larger sample

when desired, with a consequent improvement in sensitivity

of detection, while retaining the improved reproducibility

of single-spike compared to multiple -spike operation.

The time-course of events between arrival of the laser pulse

at the specimen and the excitation of the vapor in the spark

should also be studied, along with the mechanisms involved

in vaporization and transport of the specimen. A problem in

quantitative analysis is the determination of the constituents

of a single micro -specimen of unknown composition. If enough

specimen is available, it is possible to first perform a

qualitative analysis and then select or prepare standards

bracketing the composition of the specimen. This will not

be possible when the specimen is so small that only one exposure can be made; in spectrographic analysis it is ordinarily necessary to run the standards at the same time as the

samples, since calibration curves commonly shift from day

to day for a variety of reasons, some of which are not known.

It may be possible to develop a technique in which the

analyses are based on direct measurement of line intensities

and the amount of material vaporized, without the need for

standards matching the composition of the sample.

(S. D. Rasberry, B. F. Scribner, M. Margoshes)

27
3. X-RAY SPECTROMETRY

X-ray spectra contain lines having frequencies

characteristic of the elements present in the radiating

material. The characteristic line emission spectra can be

simply related to the atomic number of the emitting elements

[10]; their structure is considerably simpler than that of

spectra in the visible frequency range. While the fine

structure of the emission lines is at present the object of

study and speculation, the coarser features were exhaustingly explored several decades ago.

Not surprisingly, the potential of x-ray spectroscopy

for elemental analysis was soon recognized, and methods and

Instrumentation were developed, as described by Siegbahn

[11] and Von Hevesy [12]. However, in spite of the discovery

by this method of several elements predicted by Mendeleev's

theory, x-ray spectrometry was not broadly applied until

after World War II, when x-ray detection methods of high

efficiency had become available [13] .

The Ionization leading to x-ray emission is presently

achieved in practice by one of three methods: by the impact

of particles (electrons, protons, etc.), by the action of

ionizing radiation (x-ray fluorescence), or by electron

capture in nuclear reactions. In the .first method, the

specimen acts as the target of an x-ray tube. Consequently,

the specimen is exposed to heating, to the impact of

electrical charge (which has to be removed by conduction),

and to the chemically destructive action (particularly for

organic matter) of the impinging particles (commonly

electrons). Furthermore, the specimen must be mounted

within the vacuum chamber of the Instrument, For these

reasons, the second method, excitation by x-ray fluorescence

is preferred. Here the specimens may be kept outside the

primary vacuum enclosure and analysis can be made of a wide

variety of materials Including liquids, electrical and

thermal Insulators, and organic materials.

A. Capabilities of X-Ray Fluorescence Spectrometry

1. Elements that can be analyzed ; All elements of

atomic number three or higher emit x-rays. While the

frequency of homologous x-ray lines is strongly dependent

28
upon the atomic number, the existence of several series of

x-ray lines (K, L, M ...) assures the availability of lines

within a useful frequency range for almost all elements.

The only exception Is given by the elements of atomic number

below 12, with all of their x-ray lines within the very

"soft" range of wavelengths greater than lo8. Commercially

available Instruments usually cover the elements of atomic

number 12 (Mg) or higher; Instrumentation for the

determination of lighter elements Is presently under

development [l4] ,

2

,

Range of Concentrations being Investigated; The

Inherent sensitivity of the method Is typically 20 to 200

ppm, depending on the Instrument, the nature of the

specimen, and the atomic number of the element to be

determined. Measurements of major components are very

frequently made. Thus, the range of x-ray fluorescence,

although overlapping considerably with that of light

emission spectrometry, tends towards higher concentrations.

It Is, however, possible to combine chemical preconcentratlon methods with final read-out by x-ray spectrometry.

Fractions of a microgram can be measured In this way, after

separation of one element or a group of elements from the

major constituents.

3. Precision and Accuracy : With modern equipment and

due precautions, the precision attainable In x-ray

intensities can be made better than that of most conventional chemical analytical methods, if the statistics of

quantum counts are taken into account. Therefore, x-ray

fluorescence analysis is probably the most successful

competitor of quantitative "wet" chemical analysis. The

x-ray intensities received from an irradiated specimen

depend upon the extent of attenuation of both the primary

(exciting) and the secondary (fluorescent) beam. This

attenuation is a function of the concentrations of all

constituents of the specimen. Tertiary emission of x-rays

excited by the fluorescent x-rays may also occur, and its

presence and Intensity is also dependent upon specimen

composition. Consequently, analytical curves are generally

nonlinear for binary systems, and the complexity of the

"interelement effect" increases rapidly with the number of

constituents. Unless standards of composition close to that

of the specimens are available, or correction procedures

lb

29
for these effects can be developed, the accuracy of the

method may be considerably poorer than Its precision. The

problems Involved in the development of such correction

procedures have been recently discussed in a two-day informal

meeting arranged by our group at the NBS with assistance of , several x-ray spectroscopists of the United States and ) Canada, A report covering the meeting is in preparation.

The critical study of proposed techniques for the solution

of this problem is one of our research goals. ,

The calculation procedures mentioned above assume that

the specimen is completely homogeneous. Inhomogeneity and ' particle size variations in particulate specimens constitute

another potential source of errors. |

B, Modifications of X-Ray Fluorescence Equipment

The Spectrochemical Analysis Section is at present

equipped with a single channel x-ray fluorescence

spectrometer (the Norelco Three Specimen Position Spectrometer), chiefly used for research and development purposes,

and a multi-channel x-ray fluorescence spectrometer (ihe

Applied Research Laboratories, Inc., PXQ) for rapid routine

or semi-routine analysis of a large number of specimens.

These instruments were purchased in 1957 and I958,

respectively.

1. Single Channel Spectrometer ; This instrioment,

figure 10, consists of the following sections:

a. An x-ray generator, consisting of a power

supply and a properly shielded and cooled x-ray tube with

side window,

b. A specimen chamber section with provisions

for introducing, positioning, and exchanging the specimen

to be excited by the primary x-rays,

c. An x-ray spectrometer unit, consisting of a single crystal for monochromatization of the secondary xrays emitted from the specimen, collimators defining the

direction of the x-rays before and after diffraction, a mechanical assembly assuring proper angular relations

according to Bragg 's law of the aforementioned components

30

i

I
Figiore 10, Single channel x-ray fluorescence

spectrometer. The spectrometer unit is

on top of the cabinet to the right. The

middle console houses the voltage supply

for the detector; the sealer-timer

combination with ratemeter, the signal

amplifier and conditioner, and the chart

recorder for the ratemeter output. On

the left, the power supply for the x-ray

generator, and, on top, a single channel

pulse height analyzer and an electronic

timer.

31
during the diverse operations, and an x-ray detector

receiving the x-rays colllmated after diffraction.

d. An electronic assembly for read-out of the

x-ray signal produced by the detector. This assembly

Includes the power supply for the detector, signal

amplifiers, a single channel pulse height analyzer, a scaler-tlmer combination for quantitative measurements, and

a ratemeter chart recorder for qualitative and semiquantitative operations.

Considerable progress has been made In the Instrumentation for x-ray fluorescence analysis since the

acquisition of the present Instrument. It was therefore

decided that a modernization of this equipment was necessary

In order to permit Its efficient use for research purposes.

The components which are mentioned below In detail have

been ordered and are presently being Installed and tested:

a, A new x-ray tube assembly permitting quick j change of x-ray tubes with diverse target and window < characteristics, i

I b, A new assembly for the specimen changer and

the spectrometer unit which permits operating the entire

x-ray optics in vacuo or within a helium atmosphere,

c, An arrangement permitting the alternative or

simultaneous use of gas flow proportional detector and a scintillation detector.

d, A new electronic panel Including an improved

pulse height analyzer and a fully electronic timer.

The chief purpose of the these improvements is to

extend the useful gange of the Instrument to the wavelength

region between 2,5A and lOA, This wavelength region is at

present of great practical Interest, Work in it should also

give us the proper background for future exploration of the

"ultrasoft" region (lO-lOOA), which is most interesting

from the point of view of advanced research.

2. Multi-channel Spectrometer: This instrument,

figure 11, differs from the previous instrument by the fact

32

1
Figure 11. Multi-channel x-ray spectrometer.

Left, x-ray tube power supply;

center rear, spectrometer proper;

right, signal Integrating and

conditioning console; center front,

digital converter, programmer, and

typewriter read-out with tape punch.

33
that an array of monochromators, arranged radially around

the end -window x-ray tube and the specimen, permits the

simultaneous registration of x-ray Intensities at several

wavelengths. All but two of the monochromators are

permanently adjusted to a selected fixed wavelength, so

that the array of elements measurable by the fixed channels

Is pre-determlned by the original programming. When the

Instrument was purchased the programming Included soft x-ray

spectrometers for the elements from magnesium (12) to

sulfur (16) as well as one channel for calcium (20), In

the meantime, the Interest for routine analysis has shifted

toward alloys containing heavier elements only; moreover,

the analysis of soft radiation necessitates the use of

vacuum or helium paths for the x-rays, and this caused

technical problems In the multi-channel Instrument that

were never satisfactorily resolved. It had therefore been

decided to replace the long wavelength channels by channels

for heavier elements. At the same time, other components,

particularly some connected to the power supply, were to

be upgraded as well. This work has been completed. At

present, the multi-channel unit has l8 fixed channels,

tuned to the K alpha lines of the nine elements from

titanium (22) to zinc (30), of zirconium, niobium,

molybdenum, sliver, tin, and antimony, and to the L alpha-1

lines of tungsten, gold, and lead. Each of the two

scanning sections covers the wavelength range of 0.4 to

3.5^; by their use, two additional elements can be added

to the range of the Instrument. Present electronics for

read -out permit the simultaneous use of up to 12 channels.

(K. F. J. Helnrich)

C. Accuracy of Solution X-Ray Spectrometrlc Analysis of

Copper Alloys .

To certify the composition of NBS Standard Reference

Materials, It Is desirable to use at least two Independent

analytical methods to reduce the possibility of bias In the

results. X-ray fluorescence spectrometry, with Its high

precision, can serve as one of the methods If the factors

affecting accuracy are recognized and evaluated. The

ultimate In reliability Is attained by using a directcomparison method In which the unknown and the synthetic

standard are uniform. Identical In composition, and (ideally)

exposed to the excitation source at the same time,

34
By using solutions of the unknown and synthetic

standards, homogeneity Is assured and after a preliminary

analysis of the unknown, a synthetic standard closely

approximating the composition of the unknown can be

prepared. Moreover, differences In absorption and enhancement effects between unknown and standard can be

reduced by dilution.

In the comparison of solutions of an unknown and

synthetic standard, several factors may be expected to

contribute to error:

a. For solution cells having thin films as

irradiation windows, the films of the two cells may

distend by different amounts thus changing the surface

and consequently the fluorescent intensity,

b. The acid concentration may differ in the two

cells producing different absorption effects,

c. During the irradiation period, the temperature

increase may be sufficient to affect the density of the

solution.

These factors were investigated for the determination

of copper and zinc in the cartridge and aluminum brasses

which were being analyzed for certification as IffiS Standard

Reference Materials, The results of the investigation were

published in a report [15] which will be briefly reviewed

here,

1, Experimental

A commercial, multichannel spectrometer of the

curved cyrstal type, the main features of which were

described earlier, was used for this study. Additional

details are given in table 4,

The solutions were contained in cells of methyl

methacrylate plastic with an opening of 25 mm across

which was cemented -J—mil Viylar film as an Irradiation

window. The volume of the cells was approximately 11 ml.

35
Table 4. X-ray spectrometer settings.

Wavelength Crystal

Element S Radius Material Atmosphere Detector

Copper Ka 1.542 10 cm LIF

(4 m.)

Zinc Ka 1.437 28 cm LIF

(11 In.)

Air Proportional

Air Proportional

2. Effect of Film Position

The effect of changes In film position was

determined by using the solution cell and micrometer head

assembly as shown In figure 12. The micrometer head could

Figure 12. Apparatus to measure the position

of the film.

36
be read to 0.01 mm. The position of the film could be

changed by operating a small syringe attached temporarily

to the stopcock. The cell during excitation was mounted

on its edge, and the solution caused the film to distend

0.4 mm by hydrostatic pressure. Bowing the film an

additional 0.10 mm from this position caused the zinc Ka

intensity to change 0.19^ and the copper K^ intensity to

change 0.069^.

3. Effect of Acid Concentration

A 0.38^ decrease in zinc intensity resulted from

the addition of 1.6 millimoles of nitric acid to 10 ml of

a solution of brass which was 1 molar with respect to

nitric acid and had a concentration of 10 mg of brass per

ml. Under the same conditions, a similar increase in nitric

acid concentration resulted in a 0.48^ decrease in copper

intensity.

4. Effect of Temperature

A calibrated thermistor was placed in a cell to

measure the temperature rise resulting from a two-minute

irradiation period. The observed temperature rise of 0.1°C

did not significantly affect the intensity measurements.

5. Analytical Results

Comparing solutions of unknown brass samples with

a closely-matched synthetic standard and closely controlling

acid concentration and film position, the results shown in

table 5 were obtained.

6. Discussion

Improvement in precision for this method lies in

better control of instrument instability.

Since the accuracy of this method depends on closely

matching the composition of solutions of samples and

synthetic standards, a preliminary examination of the

sample should be made. It is necessary to note

particularly the presence of elements having principal

x-ray radiations lying several tenths of an Angstrom

shorter than the absorption edge of the analytical line

of the analyte and also those elements which have large

mass absorption coefficients at the wavelength of the

analytical line.

(R. Alvarez)

37
Table 5. Comparison of chemical and x-ray

results.

NBS : Samples

Number: Element

: Chemical;

:Results^:

X-Ray , Results^

: Standard

: Deviation

:of the Mean^

: Coefficient

:of Variation

:of the Mean

CllOO Cu

Zn

67. 4o

32. 2g

67. 3o

32.2^

0.07

0.03

0.10

.09

CHOI Cu

Zn

69. 5o

30.34

69.60

30.28

0.07

0.04

.10

.12

C1102 Cu

Zn

72.8.

27. Ig

72.85

27. Og

0.06

0.03

.08

.12

C1118 Cu

Zn

75. O7

21. 9i

75.

Og 21.9^

0.09

0.04

.12

.16

C1119 Cu

Zn

77. I2

20.53

77.2

20.4^

0.05

0.03

.07

.15

C1120 Cu

Zn

80. Ih

18. lo

80. 2„

18.1^

0.05

0.02

.06

.12

aAverage reported on provisional certificate. Cu determined

by electrodeposition; Zn by a double precipitation with

H2S followed by ignition to the oxide.

Mean of 8 runs.

^Standard deviation of the mean s = II^—^ , where d is

V n(n-l)

the difference of the determination from the mean, and n

is the number of runs.

^Coefficient of variation of the mean, C.V. = ^^^-^ , where

C is the average concentration in percent.

38
D. Interelement Effects In the X-Ray Spectrometrlc

Analysis of Gold Alloys.

In x-ray fluorescence analysis the concentration of an

element is in general not a linear function of the emitted

x-ray line intensity. Interelement effects of absorption,

enhancement J and line overlap generally produce nonlinear

calibration curves when curves are developed for a wide

range of compositions. If all specimens in the analysis

have nearly the same matrix, that is, the composition range

is small, it is usually possible to plot a single, linear

calibration curve for each element determined.

This was the case (figure 13) in the method of x-ray

118X10

70 74 78 CONCENTRATION OF GOLD.82

Figure 13. Calibration curve

for gold in gold

alloys, linear case.

spectrometrlc analysis of noble metal dental alloys

developed by Mulligan, Caul, Rasberry, and Scribner in the

Spectrochemlcal Analysis Section and recently published [ I6 ]

The method was specifically established for the quantitative

determination of Au, Ag, Cu, Pt, Pd, and Zn in a set of

dental gold alloys having the limited range of concentrations,

in percent: Au 68 to 79^ Ag 8 to l4, Cu 6 to 12, Pt to 6,

Pd to 3» and Zn to 2. Linear calibration curves are

used and the agreement with chemical analyses, + 0,2fo, Is

39
satisfactory for quality control. It has marked

advantages of speed and simplicity compared to chemical

analysis.

Recently, J. D. Eick, research associate of the

American Dental Association in the NBS Dental Section,

attempted to apply the method to the analysis of a set of

dental gold alloys having a wider range of compositions.

The precision in this analysis remained good; however, the

values for Au and Ag were inaccurate for specimens having

compositions outside the range of compositions in the

original work. Errors as great as + 85^ Au concentration,

and -2^ Ag concentration occurred in the analysis of Au - Ag

binaries in which the concentration of Ag was a factor of

3 greater than in the case of the original work. These

inaccuracies appeared to increase systematically when the

amount of Ag was increased in the binaries,

A detailed study of the surface preparation of the

specimens was undertaken by Eick in an effort to account

for the analytical discrepancies. No improvement over

the originally suggested surface preparation technique

could be obtained with more refined techniques.

When it was seen that additional or different surface

preparation offered no solution to the problem, the first

approximation assumption of linearity was dropped and the

problem was considered as a matrix effect problem. To

correct for possible matrix effects, concentration was

treated as a function of line Intensity affected by a

summation of contributions from every element in the

matrix. This function can be made linear by multiplication

of each summation term by the appropriate correction

coefficient. To empirically determine these coefficients

for any specific series of specimens, a mathematical

technique given by Lucas-Tooth and Price in 196I [17 ] was

applied. This treatment requires the solution of N+2

simultaneous equations, where N is the number of elements

present. All of the required computations were

programmed for digital computer processing.

As corrected by this mathematical treatment, the

analytical method now provides analyses which agree with

chemical analyses to ± 0.2^ concentration, over an extended

range of compositions, figures i4 and 15. Currently, Eick

is analyzing 300 specimens using this method and the x-ray

equipment in our laboratory.

40
85 -

I 1

80 -

i5 v/^/'

S^5 - / ./ - °/' • - BINARIES, Au-Ag z y o - BINARIES, Au-Pd 70 /'/ 0- BINARIES, Au-Pt e- BINARIES, Au-Cu D- COMMERCIAL ALLOYS

65 L A - STANDARDS /

A .1!.-'! fi? 1 66 70 75

' 80

1 85Ill90

CONCENTRATION, % Au

95 100

Figure l4. Analytical curve for

gold alloys, nonlinear

case, uncorrected.

100

95

90

-

1 1 1 —

5

7:

f 85 //

X /

^» 80 - • - BINARIES, Au-Ag,

" Au-Pd, Au-Pt,

Au-Cu

75 / D-- COMMERCIAL

ALLOYS

70 - / A-- STANDARDS

RS

/ 1 1 1 70 75 80 85 90 95 100 %Au. CHEMICAL

Figure 15. Comparison of gold

determinations by chemical

and x-ray method. X-ray

results corrected by the

Lucas-Tooth method.

41
A detailed account of the experimental work and the

final form of the correction to the method has been prepared

for publication [l8 ] .

(S. D. Rasberry, and J. D. Elck)

E. X-Ray Spectrometrlc Analysis of Silver Alloys

Conventional silver-base alloys for amalgamation with

mercury and use In dental restorations have the nominal

composition. In percent, of silver 69, tin 26, copper 4,

and zinc 1. Quantitative determination of these four

elements by traditional methods of solution chemistry Is a

time -consuming task when undertaken for more than a few

specimens. Every three years, the Research Group of the

American Dental Association, In the Dental Section of NBS,

requires analyses of 8O-IOO of these alloys, an undertaking

which requires six months for a chemist to complete. In

cooperatl on with the Dental Section, we have undertaken to

establish a method for analyzing these alloys, using x-ray

fluorescence spectrometry. We are currently testing the

precision and accuracy of a tentative method. Preliminary

results Indicate that analyses of sufficient accuracy can

be obtained for 100 specimens in two man-weeks.

The alloys, as commercially prepared for dental use,

are fine -grain turnings which vary in particle size by

about one order of magnitude, from 4o to 400 microns. For

the first preparation technique tried, a loose packing of

the grains, no simple function would relate Intensities to

concentrations, probably due to the grain size variations.

Simple solution analysis was attempted vith little success,

because of tin precipitation. Chemical separation techniques

were not considered practicable because of the increased

sample preparation time. Centrlfugally-cast molten alloy

techniques were investigated; however, inaccuracies were

apparent for the more volatile elements, suggesting

volatilization losses. A pelletizing technique, with boric

acid binder, was also tried; however, samples could not be

reproducibly made. A fifth sample preparation technique,

perhaps the simplest to apply, was examined. In this

technique the grains were pressed at 20,000 psi, with no

binder, to form a solid disk with diameter of J in. and about

3/16 in. thick. In our preliminary examination, these

briquettes have proven to be representative of the specimen,

reproducible in preparation, and easy to handle, store and

fabricate.

42
Instrumental techniques for this analysis were

directed toward rapid analysis by use of the multichannel

x-ray fluorescence spectrometer previously described • Weare currently undertaking to optimize the spectrometer

program for this analysis*

Analytical curves relating Intensities of Kq lines to

concentrations of Ag^ Cu^ and Zn were found to be linear

as shown In the example In figure l6. However^ the

6

I

1 1 1 1 1 I I

— y^

O j/^ < JO

o

z /Oy

ol I I I I I 1 1 600 INTENSITY Cu Ka

Figure l6. Linear calibration

curve for copper in

silver alloys.

function for SnKa was found to be nonlinear because of

interference from the unresolved AgKp line. To

mathematically resolve the intensity of SnKa from AgKp, the

ratio of intensities (SnKa + AgK3)/AgK,a was plotted versus

the ratio of concentrations Sn/Ag. The term AgKp/AgKa in

the intensity ratio is a constant, yielding a simple

intensity ratio plus constant, versus a concentration ratio.

This analytical curve is linear and can be used to determine

Sn in an unknown, after Ag has been determined (figures 17

and 18) . Computer programs to handle the bulk of the data

reduction are presently being written.

43
1 1

o

5 27 Z - -

Zo

<

anz

- o

o

-

z26

- o

1

o

o

1

-

700 7S0 INTENSITY SnKa

Figure 17. Non-linear calibration

curve for tin in silver

alloys.

68 90 92 94 96 INTENSITY RATIO (Sn Ka + AgKBVAgKoCxiOO)

Figure 18. Corrected calibration

curve for tin in silver

alloys

44
All that remains to complete the study of this method

is a careful determination of precision and accuracy of

the method. When this is completed, details of the work

will be prepared for publication,

(S. D. Rasberry and A. M. Yezer)

F. Determination of Coating Thickness

A preliminary study of nickel plating thickness

measurement by x-ray fluorescence was performed using the

Norelco single channel spectrograph. This work was

requested by F. Ogburn, Electrolysis and Metal Deposition

Section, NBS, Metallurgy Division, who provided specimens

of steel with-nickel platings of known thickness, from

0.0001 in. to 0.002 in. Both Ni K alpha and Fe K alpha

radiation were employed. It was established that the Ni K

alpha radiation is useful from a coating thickness far

below the range provided to us, to about 0.0002 in., and

that a range from 0.0001 in. to 0.001 in. could be covered

by the Fe K alpha radiation. Instability problems

associated with the scintillation detector of the unit

precluded an assessment of the precision of the method; no

further work is projected until installation of the

vacuijun spectrometer.

(K. F. J. Heinrich and S. Schuhmann)

45
4. ELECTRON PROBE MICROANALYSIS

Analysis of a micro-volume within a specimen is

achieved with the electron probe microanalyzer by

directing to the specimen surface a finely focused beam of

electrons. Under typical conditions, the resulting x-ray

emission is limited to a depth of one to three microns and

comparable diameter. The electron beam can be made to scan

over a small area on the specimen by applying electrostatic

deflection. The brightness of the oscilloscope beam which

scans in synchronism with the electron probe beam is

modulated by the x-ray signal, and the x-ray image thus

formed on the oscilloscope screen is recorded photographically.

Besides the purely qualitative information obtained

by these x-ray images, semiquantitative recordings of line

scans on the specimen and wavelength scan recordings can

be performed, usually on a chart recorder. Quantitative

determinations are based on counts of x-ray quanta on a sealer-timer combination.

Auxiliary signals other than x-rays complete the

information obtainable with this instrument. The

observation of electron backscatter, either directly or by

specimen current measurements, provides an excellent imageforming function, figure 19, which combines topographic

and atomic number information, since backscatter of

electrons increases with increasing atomic number. Another

signal of considerable utility is the emission of visible

light under excitation by electrons (cathodoluminescence)

,

Thus, the instrument offers a wide choice of read -out

functions and read-out modes, and a Judicious selection of

procedure must precede the analysis of each specimen.

Much effort was expended this year in the procurement,

installation, and modification of a suitable electron probe;

this instrumentation will be discussed in detail,

A. Basic Equipment

The Applied Research Labs., EXM Microanalyzer,

figure 20, as originally received from the manufacturer

is composed of the following elements:

46
target current

inverted

target current

Ag L„ x-ray

back scattered

electron

Figure 19. Electron and x-ray scanning Images. Large grid:

copper wire, 50 |J, diameter _, open space 85 \i wide.

Small grid: silver wire 4 \i diameter,, open space

20 [I wide.

^7
Figure 20. Electron Probe Microanalyzer. From left to

right: Test scope used for trouble-shooting

and installation. Recorder bay with 4-

channel recorder, and detector power supply.

Scaler panel, with scaler, timer, scaler power,

supply, and ciorrent meter. Scanning bays,

with AC and DC amplifiers, scan drivers,

signal switch board, linear amplifiers and

pulse height analyzers, and tv;o oscilloscopes,

with oscilloscope camera. Main console,

containing electron optics, sample chamber,

microscope, and three x-ray monochromators.

Power consoles, with povjer supplies for

electron emission and acceleration, and for

electromagnetic lenses; and vacuum gages.

48
a. The main console, containing the vacuum

enclosure and vacuum pumps, the electron gun and anode

assembly, two electromagnetic lenses for focusing the

electron beam, the specimen manipulator and light microscope

for specimen observation, and three x-ray spectrometers

each with two interchangeable crystals.

b. The service console, containing power supplies

for filament current and high voltage for electron

acceleration, power supplies for the electromagnetic lenses,

and vacuum measurement equipment.

c. The scanning console, containing the sweep

generators and amplifiers, modular equipment for

manipulation of AC and DC signals, two oscilloscopes for

viewing and photographing of scanning images, and three

linear amplifiers with pulse-height analyzers.

d. The read-out console, containing the power

supply and attenuators for the x-ray detectors in the main

console, a microammeter for measuring the beam and target

currents, and the sealer-timer assembly with associated

power supply.

B. Modifications of the Equipment

A program of modifications of the equipment and

additions to the equipment was undertaken in order to

improve its reliability and versatility. The following

major changes have been made:

a. The d-c amplifiers were modified to provide

greater sensitivity and facilities for inversion of blackwhite values of target current scanning images.

b

The integrators were modified to provide variable

time constants when used as ratemeters, and to provide

signals indicating unbalance condition of the operational

amplifiers

c. Extensive re-wiring was performed in order to

diminish the amount of external connections necessary for

operation.

The following elements were added:

a. A periodic integrator, built by the NBS electronics

laboratory, according to schematics developed elsewhere

[19] .

49
b. A concentration mapping [19] device also built

by the NBS electronics laboratory.

c. A phototube detector for scanning cathodoluminescence images (NBS electronics laboratory)

d. A Sanborn four-channel recording system model

854-5460, including four linear amplifiers, with heated

recording stili, for simultaneous recording of up to four

signals.

e. A voltage-to-frequency converter for quantitative

measurement of beam and target (specimen) currents.

f. An operational amplifier (solid state) for currentto-voltage conversion of target and beam current, to be

measured by item e, and for obtaining high-contrast target

current scanning images. (NBS electronics laboratory).

g. A Tektronix type 564 Storage Oscilloscope, with a

dual trace linear amplifier 3A6 and a timebase with delay

line 3B4. This scope is used for diverse testing functions,

and particularly for observation of the height and shape of

the amplified x-ray pulses.

h. A monitor circuit with variable delay line enabling

a direct observation of the single -channel pulse-height

analyzer performance on the pulse display of the

oscilloscope mentioned under g. This is accomplished by

blocking out that part of the oscilloscope trace corresponding to the pulses which are accepted by the pulse height

analyzer window. This device was developed in our

laboratory and will be described in a technical note soon to

be published elsewhere.

Extensive re-wiring with provision for centralized

switching facilities is planned in the near future. This

will markedly reduce the excessive amount of patching

currently necessary for operation, while conserving the

flexibility of the instrument.

The following additions to the microprobe laboratory

are planned for the near future

a. Equipment for the detection and measurement of

ultra-soft x-radiation will be installed by the manufacturer

in July. This will extend our capabilities to the elements

fluorine, oxygen, 'nitrogen, carbon, and boron.

50
b. Externally variable detector slits for better

adjustment of the signal-to-noise ratios and solid state

pre-amplifiers for noise-free signal amplifications will

at the same time be installed in all spectrometers.

c. A second voltage-to-frequency converter, and two

additional scalers, will permit (l) simultaneous scaling

for up to three x-ray signals, (2) scaling of up to two

x-ray signals for fixed integrated beam or specimen current,

or (3) scaling of target current, plus one x-ray signal,

for integrated beam current.

d. A multi-channel pulse-height analyzer with a 160Ochannel memory will be installed. This instrument will

permit efficient pulse height analysis and study of detector

characteristics. In addition, the memory banks will permit

the storage of a two-dimensional array of fixed-time counts.

This analyzer will include typewriter print-out and tapepunching in the ASCII code of the memory contents, as well

as paper tape feed into the memory, and will therefore

serve as an interfacing device from the microprobe to

computer facilities.

e. A precision microammeter, sensitive to 10" -^ amp

full scale, with provisions for measuring current, voltage,

and integrated current, will be purchased.

f. The auxiliary equipment for specimen preparation

and inspection, presently consisting of specimen polishing

tables and a Leitz Ortholux microscope will be expanded by

the acquisition of an ultra-microtome and an ultra-vacuum

metal evaporizer.

C. Program of Investigations

The program of activities in the field of electron

probe microanalysis will cover investigation of methods and

instrumentation, exploration of new fields of application,

and analyses in areas of interest to the NBS and other

Government agencies that lack capabilities in this technique.

Topics considered for investigation in the near future are:

a. Use of specimen current measurements for

quantitative analysis; methods and instrumentation.

b. Instrumental characteristics of x-ray detectors;

coincidence loss correction, and pulse height variation

as a function of counting rate.

c. Standard reference materials for calibration in

quantitative microanalysis.

51
d. X-ray line shifts, intensities, and band shape

variations as a function of composition; their influence on

measurements for quantitative analysis.

e. Use of memory storage and of analog computers for

rapid quantitative analysis of specimen homogeneity.

f

Development of graphic techniques for read-out of

scanning operations (concentration mapping), and development

of the corresponding instrumentation. Later objectives

should include the study of spectra in the ultra-soft range

10-100 a), and use of signals other than x-rays

cathodoluminescence, infrared emission, etc.)

D. Applications

Considerable time and effort has been spent in

satisfying the demands for microanalyses for the NBS as

well as for other agencies requesting such service from the

NBS. The following list will illustrate the type of

service performed:

a. Analysis of a specimen of platinum-rhodium

standard, for identification of material in grainboundaries.

b. Analysis of two specimens of micro-film.

c. Analysis of two specimens of gallium arsenide, for

dopants.

d. Analysis of turbine inlet guide vane specimens.

Figure 21, study of cracked zone.

e. Analysis of fragment of airplane landing gear

piston assembly. Composition of a welded area, inclusions,

and cracks.

f. Analysis of corroded Monel metal. Identification

of phase in grain boundaries of corroded area.

g. Identification of a metallic particle extracted

from the eye of a patient.

h. Comparison of three metal particles with a

standard steel specimen.

This representative, although incomplete, list

illustrates the range of problems of interest to the NBS

that can be handled with the raicroprobe.

52
*««%4v/'' -l^-.'

"^; - . .

1^ .?^-i,*

A

CrKa

B

AIKo,

Figure 21. Chromium (A) and aluminum (b) x-ray scans

of a cracked segment of a turboprop inlet

guide vane; showing enrichment of these

elements (brightness) within the crack

due to preferential oxidation.

The preceding list represents the non-recurrent type of

analysis of a single or few specimens. Systematic studies

of certain problem areas have also been underway, notably

that of homogeneity of NBS standard reference materials.

A study of microstructure and homogeneity of dental alloys

is presently in preparation. Exploratory work is also

being done on possible applications of the microprobe to

the analysis of archeological specimens of interest to the

Conservation Laboratory of the Smithsonian Institution.

(K. P. J. Heinrlch)

53
5. ANALYSIS OF HIGH-PURITY METALS: ENRICHMENT METHODS

A primary research effort of the Analytical Chemistry

Division Is to develop methods for detecting and

quantitatively measuring slight traces of Impurities In

matter. Hlgh-purlty materials are essential for applications

In metallurgy, nuclear engineering, quantum-light generators,

and solid state devices. The development of NBS Research

and Standard Reference Materials In these areas emphasizes

the Importance and need for sensitive and accurate methods

for the analysis of hlgh-purlty materials. For a

preliminary characterization of hlgh-purlty materials as

suitable reference materials. It Is desirable to know which

elements are present, their concentrations, and homogeneity.

For this preliminary examination, the spectrochemlcal method

should have hlgh-sensitlvlty for many elements, be rapid,

and be relatively free from contamination. Since the

concentrations of many elements In the materials are often

below the levels at which they can be detected by

conventional spectrochemlcal methods, enrichment procedures,

either physical or chemical, are required. These will be

discussed for the analysis of three high purity metals:

tin -- Important In solid state devices, zinc -- a proposed

standard reference material for freezing point and composition, and platinum -- a proposed research material.

A. Physical Enrichment

If a simple enrichment process can be performed without

the necessity of dissolving and separating the elements to

be determined, the requisite rapidity can be realized. It

was felt that this could best be accomplished by

fractionally distilling the Impurity elements from the

matrix. While not new, the method Is quite effective In

extending the sensitivity to low concentration. In this

procedure, the sample is arced continuously as the camera

is being racked at definite intervals. Since the spectral

lines of volatile elements appear first and the more

refractory elements appear later, the exposure can be

selected which yields the best spectral line to background

ratio. It was found that by flowing an argon-oxygen gas

mixture past the arc instead of arcing in air, and using

higher spectral orders, greater sensitivities for some

elements could be realized.

1. Analysis of Tin , As applied to the analysis of hlgh-purlty tin, a

cylindrical sample pellet approximately 4 mm in diameter by

4 mm long was placed in a cupped, graphite electrode and

arced to completion with a direct current of 20 amp using a

54
graphite counter electrode and an analytical gap of 3 mm.

As the sample was arced, the camera was racked at 20

second intervals and the spectra recorded on Eastman Kodak

SA No. 1 photographic plates. First order spectra were

taken in the wavelength region from 2200 to 4700 a; the

reciprocal linear dispersion was approximately 5-0

Angstroms per mm. A slit width of 15 microns was used.

"Addition standards" were made by melting weighed

^amounts of an NBS standard reference material of tin,

'No. 435, with the high purity tin sample to be analyzed

in a quartz tube under cottonseed oil. By drawing the

molten metal into Pyrex tubes, rods 4 mm in diameter were

formed from which the sample pellets were cut. This

provided a series of reference samples containing known

amounts of Cu, Pb, As, Sb, Ni, Zn, Ag, Bi, Cd and Co. The

surfaces of the samples were cleaned by treatment with

dilute, distilled HCl. It was found that Cd, Bi, Ag, Pb,

and Cu could be detected at an approximate concentration

of 0.1 ppm, Ni at 0.2 ppm and Sb at less than 0.5 ppm.

Preliminary experimentation using a 20^ oxygen-805^

argon mixture surrounding the electrodes, and superimposing the spectra from the first 20 second arcings of

two sample charges, indicated that bismuth could be detected

at a concentration of less than 0.1 ppm.

2. Analysis of Zinc

A sample of zinc, a proposed standard reference

material for composition and melting point standard, was

examined using this method, six metallic impurities, Ag,

Cd, Fe, Mg, Pb and Si, were detected with concentrations

totaling approximately I.2 ppm. To cut the 4-mm diameter

sample pellets, a special tool consisting of a steel tube

edged with a tool steel cutter was used. It was found

necessary to remove approximately Q% of the surface area of

the pellet by dissolving In dilute, distilled HCl to

eliminate contamination from the sampling operation.

3. Analysis of Platinum

Two samples of platinum, proposed research materials,

have been examined by this method. The two lots, largely In

0. 020-Inch diameter wire form, will serve for interlaboratory comparisons of analyses and electrical

measurements. One material, designated as Pt No. 174471,

contains 1 to 10 ppm of at least 13 elements. In addition

to the elements ir, Rh, Pd, Ag, Au, Ca, Pb, Mg, and Cu

incorporated In the master alloys from which the final

melt was made, Fe, Si, Al and Zr were detected. The Zr,

tt

55
from the ZrOg crucible which was used by the manufacturer,

has such poor spectral sensitivity that it usually is not

detected in the spectrochemical procedures ordinarily

employed. A 100-mg sample charge was arced using a current

of 15 amp, and other conditions as had been used for the

analysis of tin. An atmosphere of 20^^ oxygen-805^ argon

was found superior to that of air for the detection of

zirconium. The other material, Pt No. 273^ is a lot of

highest commercial purity; here Cu, Si, Fe and possibly Ir

were detected.

In addition, several other materials, intended to be of

high-purity, were examined by this procedure: magnesium,

for experimentation prior to atomic weight determination;

copper made at MBS, Boulder for electron scatter measurements; and samples of lithium-gallium and lithiijm -aluminum

purchased as being "free" of iron, cobalt, nickel, and

chromium. The copper was found to be of superior purity -- only magnesium was detected, at less than 0.2 ppm. The

"high purity" magnesium metal was found to be less pure than

a magnesium reference material in our stock; some of the

latter metal was supplied to the research group for its use.

(in many instances research groups are not aware of the

better sources of high purity materials and we have furnished

information on the sources or supplied the material from

our stock) . The lithiijim compounds were found to be impure,

with Fe, Co, Ni, and Cr each greater than 0.0015^.

B. Chemical Enrichment

Chemical enrichment -spectrographic methods involve

dissolving the sample and employing separation techniques

such as ion-exchange, solvent extraction, electrolysis, or

selective precipitation to separate the impurity elements

from the major constituent and provide a concentrate. By

comparing the concentrate containing the impurity elements

with synthetic standards, quantitative determination of

the elements can be made without the necessity of separating

the individual elements. The requirements for dissolving

the sample, stringently purifying the reagents used,

avoiding contamination from the environment, and investigating possible losses of the separated traces by absorption

effects make these methods time-consuming and unsuitable as

rapid survey methods for high purity materials. However,

they are important for quantitative analysis of a selected

material. Several chemical enrichment procedures are under

investigation.

1. Analysis of Tin

An extraction procedure described by Stokely and

56
Moore [20] was adapted for spectrochemlcal use. 200 mg of

tin as a chloride solution having a concentration of 10 mg

of tin per ml, was extracted with three 20-ml portions of

0,5 M TTA Ih methyllsobutylketone that had previously been

equilibrated with 3N HCl. A shaking period of two minutes

was used for each portion. The aqueous layer was placed In

a quartz dish and 1 ml of a high purity gallium sulfate

solution was added equivalent to 20 mg of GaoOo per ml.

After evaporating the solution to dryness, tne-^dlsh was

Ignited at 900°C for 15 minutes. The gallium oxide residue

was then arced to completion and compared to synthetic

standards. The removal of antimony and Iron, two Important

lmp\irltles In tin, during the extraction step constitutes a

drawback of this method.

1^

2. Analysis of Platinum

For the possible determination of Iron, aluminum,

and tin In platln\im, a procedure Is being Investigated In

which Ga(OH)o is precipitated and acts as a "gatherer" for

these elements. In this method, approximately 500 mg of

platinum was dissolved In 30 ml of aqua regla. The

solution was evaporated to dryness In a quartz evaporating

dish and excess nitrate removed by adding HCl several times

and evaporating almost to dryness. The residue was

dissolved in 2 ml HCl and the volume made up to 50 ml; 20

ml of this solution was heated and ammonium hydroxide added

to form the platinum ammlne complexes. The solution was

then made slightly acidic with HCl and 1 ml of a gallium

sulfate solution was added equivalent to 20 mg of galllxjm

oxide. On adding ammonium hydroxide, a precipitate of

gallium hydroxide formed which could be Ignited to the

oxide after centrlfuglng, and then compared to synthetic

standards. At present, some platinum is found in the oxide

and further Investigation of the method is necessary.

(R. Alvarez)

57
6. STANDARDS, ANALYSIS, AND LITERATURE ACTIVITIES

The Section provides analytical assistance to other

research groups at NBS, to other Government agencies, and

to the general public. These activities include (1)

developing standard reference materials, especially

standards for calibration in spectrochemical analysis; (2)

providing analyses in optical spectrometry, x-ray

fluorescence spectrometry, and electron probe microanalysis;

and (3) providing literature surveys in these fields

through bibliographies and critical reviews.

A. Standard Reference Materials

1. Standards Program

The program of standard reference materials and

calibration in spectrochemical analysis has been a major

activity of the Section. The output of this program has

consisted of standard reference samples with certified

composition, and the determination of information on

applying the reference samples, including methods of

analysis.

Until recently the actual preparation of standard

reference metals and alloys of solid forms was a part of

the program of the Section; however, the preparation work

was transferred to the new NBS Office of Standard Reference

Materials in 1964. The Section continues its activity on

the analysis of proposed reference materials in cooperation

with other Sections of the Analytical Chemistry Division.

The analysis of reference materials consists of two

phases, first, a study of homogeneity of the material, and

second, accurate analysis by two or more cooperators or

techniques. Homogeneity of the intended standard is

essential to its use, since each user should receive a

specimen corresponding in analysis to the certificate

provided. In spectrochemical analysis the amount of

specimen consumed in an analysis may be of the order of a

milligram or less and the analysis may be affected by the

physical state of the material. Consequently, much effort

has been devoted in our Section to the design of optimum

procedures for study of homogeneity. For spectrochemical

analysis, experiments have been designed to obtain the

maximum of information from the minimum of testing, using

photoelectric spectrometers for high precision. The

information is read out in the form of punched cards or tape

and submitted to a computer for statistical analysis of

the data. Analysis of variance serves appropriately for

58
determining that part of variation In concentration

attributable to segregation In the sample. Two large

photoelectric spectrometers are Installed In our laboratory

primarily for homogeneity testing, although they are also

used for general analytical service and research work.

The Baird -Atomic Direct Reader, figure 22, Is a 3-

meter Eagle mount of a concave grating with a reciprocal

Figure 22. Direct reading spectrometer with automatic

read -out system. Left background, electronic

digitizer for spectrometer read -out; foreground, punched -card read -out unit; right,

control end of 3-meter grating spectrometer.

59
linear dispersion of 2,8 Angstroms per mm In the first

order. An array of 58 exit silts and phototubes provides

for Intensity measurements of 36 chemical elements.

Eighteen elements may be measured simultaneously relative to

an Internal standard element and the results are displayed

on digital counting tubes. The Information on spectral

line Intensities Is printed and punched on an IBM card

within 10 seconds after the spectral exposure Is ended. In

a typical homogeneity study, some 30 samples may be

analyzed, resulting In 30 record cards. These are transferred to a computer which, by previous programming,

converts Intensity ratios to concentration and subjects

the data to analysis of variance. All proposed metallic

alloy. standard reference materials In production at NBS are

Investigated for homogeneity by this method prior to

acceptance for final analysis and distribution. Much of

this homogeneity testing has been done by D. M. Bouchette.

Similar operations are performed on an Applied Research

Analysis spectrometer, figure 23^ but with different

excitation sources and with readout to typewriter and

punched tape. X-ray fluorescence spectrometry is also

applied in homogeneity studies and in analysis using the

multi-channel x-ray spectrometer previously described

in this report. The electron probe microanalyzer is a very

sensitive tool for study of homogeneity and is applied in

critical cases.

Following the homogeneity studies, analyses of proposed

standards are made in cooperation with other laboratories

in the Division, Here the spectrochemical analysis must

be made by a primary method relative to standards

synthesized from pure materials. The samples are converted

to finely divided powders or to solutions to homogenize the

sample and to provide a form for comparison with the

synthesized standards. Powders are usually analyzed by arc

excitation; solutions by the plasma jet, by atomic

absorption, or by a spark with the rotating electrode

technique.

2. Analyses Made of Standard Reference Materials

Analyses of standard reference materials during the

12-month period from June, 1964 through May, 1965 included 39

I

60
Plgiire 23. Multi-channel optical spectrometer. At left,

excitation source console; center, 2-'meter

grating spectrometer with spark stand in

front; right, recording console with chart

recorder controls, and array of spectral

line integrators.

61
samples, with 128 qualitative determinations, and 19^9

quantitative determinations, and 19 reports written.

(Other analyses made are described below.)

B. General Spectrochemical Analyses

Spectrochemical analyses are made of a wide variety

of materials to assist other NBS laboratories and other

Government agencies where their facilities are not capable

of doing the work.

1. Types of Analyses

The large bulk of analyses are rapid surveys by

optical spectroscopy in which 50 chemical elements are

sought. Occasionally the rare earths and alkalies are

included to extend the list of elements to 70. In the

analytical report the concentrations of the elements

found are given within ranges of factors of 10, e.g. 0.001

to 0.015^, 0.01 to 0.15^ etc. This analysis often may provide

sufficient information for the problem; if not, it provides

the basis for efficient planning of further quantitative

analysis by spectrochemical or other methods.

A large grating spectrograph, a 21-foot Wadsworth

concave grating mounting, has been used in the past for much

of the optical emission analytical work. About a year ago j

a 3.5-m Ebert mount plane grating spectrograph, figure 24, " was installed to modernize and improve the facilities for

this work. This instrument provides for rapid interchange

of selected gratings and permits observation of spectra at

higher grating orders for better resolution. The arc -spark

stand mounted with this instrument provides for convenient

operation of the excitation source in various gas mixtures

Qualitative analysis may also be made by scanning

through the x-ray spectrum and this complements the optical

method. The x-ray method is less sensitive for sane of

the metallic elements but more sensitive for metalloids

and halogens.

Quantitative analyses are made by both optical and x-ray

fluorescence spectrometric methods using equipment described

earlier. The problem is relatively simple for the analysis

of metals and alloys when a solid sample with a diameter

of 1 to 2 cm is provided, and when adequate reference

samples are available. However, many samples are in the

form of powders, solutions, thin wires, or thin films.

In these cases the samples may be analyzed in the form of

dry powders or solutions, relative to standard samples

synthesized from pure elements or salts

62

I
Figure 24. Optical spectrograph, 3.4-meter Ebert.

(Control end) At the right, an arcspark stand for spectral excitation In

controlled atmospheres.

Spectrochemical methods in general may be considered

micro or semi -micro methods since a sample of 10 mg or less

may suffice for the analysis. Recent developments in both

optical and x-ray analysis have reduced the required sample

size to very small amounts thus extending the methods to

the sub-micro range. The laser probe consumes a sample

weighing about 0.1 (ig and can provide information on 50 or

more elements in this sample. The electron probe microanalyzer can analyze a volume of a few cubic microns

Weighing a picogram (lO'^^g) or less. It also provides

remarkable information on the distribution and

concentration of chemical elements in a surface. For

further details on these new analytical tools and service

applications see section 2-E and section 4 of this report.

63
2. General Analyses Made

Spectrochemical analyses, other than those made of

standard reference materials, during the 12-month period

from June, 1964 through May, 19^5 included 409 samples with

12,268 qualitative determinations and 396 quantitative

determinations, and l44 reports written.

(B. F. Scribner and E. K. Hubbard)

C. Literature Surveys

Since its inception the Section has served as a focal

point for information on the literature of optical

spectroscopy. Bibliographies on optical spectrochemical

analysis have been prepared and have been published through

the American Society for Testing Materials [21]. Biennial

reviews in this general field [ 22 ] and in flame photometry

[23]have been published in Analytical Chemistry.

To collect information on the literature, systematic

surveys are made using Chemical Titles, Chemical Abstracts,

and final checking against selected journals. Card files

are maintained with the abstract typed or pasted on 5 X 8

in. cards. At periods of about five years, the material

is indexed and prepared for publication. At the present

time preparation is nearly complete on the next volume of

the Index to the Literature on Spectrochemical Analysis,

for the years 1956-60. Similar literature reference files

are maintained for x-ray spectrometry and electron probe

microanalysis. A bibliography on electron probe microanalysis, previously prepared at the E. I. du Pont de

Nemours, Experiment Station, Wilmington, Del., is being kept

up-to-date. This year a supplement to the original

bibliography was made available through the cooperation of

the du Pont laboratory. The complete bibliography in offset form is available on request from Dr. K. F. J.

Heinrich of our Section.

Attention is currently being given to the possibility

of issuing the bibliographies at shorter intervals.

(B. F. Scribner, M. Margoshes,

K. F. J. Heinrich, and V. C.

Stewart)

64

i
7. PERSONNEL AND ACTIVITIES

A, Personnel Listing

Spectrochemlcal Analysis, Bourdon F. Scrlbner, Section Chief

Group I. Optical Spectroscopy

Marvin Margoshes, Chemist

Martha M. Darr, Chemist

Stanley D. Rasberry, Physicist

Howard E. Bond (Physicist, Summer Student 1964)

Group II. X-Ray Fluorescence Spectrometry and Electron

Probe Microanalysis

Kurt F. J. Helnrlch, Chemist

Shuford Schuhmann, Chemist (Temporary)

Detlef F. Gerlach, Chemist (Summer Student I965)

Gerald A. Wolfson. Electronic Technician

Part Time Guest Workers

Michael Duke, Chemist, U. S. Geological Survey

Harvey Yakowltz, Metallurgist, NBS Metallurgy

Division

Donald L. Vleth, Physicist, NBS Metallurgy Division

John D. Elck, Chemist, Dental Research Group

Group III. Calibration and Analysis

Harold C. Dllworth, Chemist (Resigned)

Elizabeth K. Hubbard, Physicist

Doward M. Bouchette, Physical Science Technician

Anthony M. Yezer, Summer Student 1964

Group IV. Enrichment Techniques

Robert Alvarez, Chemist

Group V. Literature Survey

Virginia C. Stewart, Chemist

Group VI. Clerical

Frances L. Hllten, Administrative Aid

65
i

B. Publications

1. Mlchaells, R. E., Yakowltz, H., and Moore, G. A.

Metallographlc Characterization of an NBS

Spec trometrie Low Alloy Steel Standard.

J. Research NBS, 68a, 3^3-354, July-August 1964.

2. Margoshes, M.,and Scribner, B. F.

Simple Arc Device for Spectral Excitation in

Controlled Atmospheres.

Appl. Spectry., l8. No. 5. 154-155, 1964.

3. Mlchaelis, R. E., Wyman, L. L., and Flitsch, R.

Standard Reference Materials : Preparation of NBS

Copper-Base Spectrochemlcal Standards.

NBS Misc. Publ. 260-2, October 15, 1964.

4. Scribner, B. P., Margoshes, M., and Rasberry, S. D.

Laser Microprobe for Analysis of Very Small Samples,

in "Research on Crystal Growth and Characterization

at the National Bureau of Standards, January to

June, 1964", NBS Technical Note 251, Oct. 19, 1964,

National Bureau of Standards, Washington, D. C.

5. Mlchaelis, R. E., Yakowitz, H., and Moore, G. A.

Standard Reference Materials: Metallographlc

Characterization of an NBS Spectrometric Low-Alloy

Steel Standard.

NBS Misc. Publ. 260-3, October 22, 1964.

6. Alvarez, R., and Flitsch, R. 2|

Standard Reference Materials: Accuracy of Solution

X-Ray Spectrometric Analysis of Copper-Base Alloys.

NBS Misc. Publ. 260-5, March 15, 1965

7. Scribner, B. F., Margoshes, M., and Rasberry, S. D.

Laser Microprobe for Analysis of Very Small Samples,

in "Research on Crystal Growth and Characterization

at the National Bureau of Standards, July to December

1964." NBS Technical Note 260, May 8, 1965,

National Bureau of Standards, Washington, D. C.

8. Scribner, B. F., and Margoshes, M.

Emission Spectroscopy

Chapter 64 of I. M. Kolthoff and P. J. Elvlng

"Treatise on Analytical Chemistry", Part I, Vol. 6,

pp. 3347-3461.

New York - J, Wiley & Sons, 1965.

66
9. Dllworth, H. C.

Spectrochemlcal Analysis of High -Temperature Alloys

by Spark Excitation In Argon and Nitrogen.

American Society Testing Materials Special Technical

Publication, (in press).

10. Helnrlch, K. P. J.

X-Ray Absorption Uncertainty

The Electron Probe Mlcroanalyzer — Proceedings of a

Symposium on Electron Probe Analysis.

Electrochemical Society, Washington. Oct. 1964

New York, J. Wiley & Sons (in press).

11. Temple, A. K., Helnrlch, K. F. J., and Flcca, J. P., Jr.

Quantitative Electron Mlcroprobe Analysis of

Ilemlte Ores.

The Electron Probe Mlcroanaly7er — Proceedings of a

Symposium on Electron Probe Analysis, Electrochemical

Society, Washington, Oct. 1964

New York, J. Wiley & Sons (In press).

12. Helnrlch, K. P. J.

Electron Probe Microanalysis

"Lectures on Modern Techniques in Solid State Research"

Garden & Breack, 150 Fifth Ave., New York, (in press).

13. Helnrlch, K. P. J.

X-Ray Optics and X-Ray Microanalysis.

Book Review, American Scientist (in press),

14. Eick, J. D., Caul, H. J., Smith, D. L., and

Rasberry, S. D,

Analysis of Gold and Platinum Group Alloys by X-Ray

Emission With Corrections for Interelement Effects.

Anal. Chem., (Submitted)^

15. Helnrlch, K. P. J.

Identification of Inclusions with the Electron Probe

Mlcroanalyzer

American Society for Testing and Materials, Special

Technical Publication,

(Submitted)

16. Helnrlch, K. P. J.

Problems in Excitation and Sampling in X-Ray

Fluorescence Analysis.

American Society for Testing and Materials, Special

Technical Publication.

(Submitted)

67
17. Margoshes, M.

Recent Advances in Excitation of Atomic Spectra.

Proceedings of the Xllth International Spectroscopy

Symposium,

Exeter, England (I965) (Submitted).

18. Rasberry, S. D., Scribner, B. F., and Margoshes, M.

Characteristics of the Laser Probe for Spectrochemical Analysis

(a Summary)

Proceedings of the Xllth International Spectroscopy

Symposium,

Exeter, England (1965) (Submitted).

19

Margos he s , M

Excitation and Ionization in Arc and Spark

Excitation Sources.

Appl. Spectry. (Submitted),

20. Scribner, B. F.

Advances in Excitation Sources for Spectrochemical

Analysis, XXth International Congress on Pure and

Applied Chemistry, Moscow (I965).

Pure and Applied Chemistry. (Submitted),

68
C . Talks Given

1. MargosheS:, M., "Excitation of Spectra: Fact and Fancy",

Society for Applied Spectroscopy, Third National

Meeting, Cleveland, Ohio.

October 2, 1964.

2. Heinrich, K. F. J., "X-Ray Absorption Uncertainty In

Electron Probe Microanalysis," The Electrochemical

Society, Washington, D. C.

October 13, 1964.

3. Heinrich, K. F. J., "Electron Probe Microanalysis,"

School of Metallurgical Engineering, University of

Pennsylvania, Philadelphia, Pennsylvania

October 27, 1964.

4. Heinrich, K, F. J., "Analytical Applications of X-Ray

Spectrometry," Analytical Chemistry Seminar, NBS,

Washington, D. C, Nov. 6, 1964.

5. Scribner, B. F., "The Role of Gaseous Atmospheres in

Spark Excitation for Spectrochemical Analysis,"

Joint Meeting, Society for Applied Spectroscopy,

Delaware Valley Section, and American Chemical

Society, Lehigh Valley Section, Reading, Pennsylvania,

November 20, 1964.

6. Heinrich, K. F. J., "The Determination of Trace

Impurities and Light Elements by X-Ray Fluorescence

Spectrometry," Society for Applied Spectroscopy,

Pittsburgh Section, Pittsburgh, Pennsylvania.

February 17, I965.

7. Rasberry, S. D,, "Quantitative Aspects of Laser Probe

Spectral" Analysis," Spectroscopy Society of

Pittsburgh, Pittsburgh Conference on Analytical

Chemistry and Applied Spectroscopy, Pittsburgh,

Pennsylvania. March 4, 1965.

8. Scribner, B. F., Michaelis, R. E., and Darr, M. M.,

"The Pittsburgh Conference on Analytical Chemistry

and Applied Spectroscopy, held March 1-5."

Discussion Meeting in Analytical Chemistry, NBS

Washington, D. C, March 24, I965.

9. Scribner, B. F., "Metallurgical Applications of Laser

Probe Analysis," American Chemical Society, Detroit,

Mich., April 5, I965.

69
1

10. Rasberry, S. D., "Spectrocheralcal Analysis by the Laser

Probe," Joint Meeting of the Chemical Society of

Washington and the Maryland Section, American

Chemical Society, College Park, Md., May 1 , 1965 . 1

11. Scrlbner, B. F., "Accuracy In Spectrochemlcal Analysis,"

Panel Discussion on Accuracy, Analytical Chemistry

Division, May 21, I965.

12. Helnrlch, K. F. J., "Electron Probe Microanalysis,"

Society of the Sigma XI, Washington, D. C,

May 10, 1965.

13. Helnrlch, K. F. J., "Identification of Inclusions With

the Electron Probe Mlcroanalyzer," American Society

for Testing and Materials, Purdue University,

Lafayette, Ind., June l4, I965.

14. Helnrlch, K. F. J., "Problems of Excitation of X-Rays

and Surface Effects of the Sample In X-Ray

Fluorescence Spectrometry," American Society for

Testing and Materials, Purdue University, Lafayette,

Ind., June l4, 1965.

\

70

I
D. Committee Activities

American Society for Testing and Materials,

ASTM Committee E-2 on Emission Spectroscopy.

B. F. Scrlbner, member, attended a meeting In Pittsburgh,

Pa., March 2, 1965.

R. Alvarez, member, attended meetings In Lafayette, Ind.,

June 15-18, 1965.

ASTM Committee E-4 on Metallography

K. F. J. Helnrlch, Chairman of Mlcroprobe Task Group

presided at meetings In Lafayette, Ind., June 15-I8,

1965.

ASTM Committee E-13 on Absorption Spectroscopy

B. F. Scrlbner, member, attended meeting In Pittsburgh,

Pa., March 1, 1965.

Chemical Society of Washington, Committee on Meetings

B. F. Scrlbner, member, attended two meetings.

November, 1964 and January, 19^5

XII Colloquium Spectroscoplcum Internationale, Exeter, 19^5

B. F. Scrlbner, member of Advisory Committee.

Eastern Analytical Symposium

B. F. Scrlbner, Program Chairman, EAS I965* attended

meetings of the Planning Committee, February 12, and

May 14, 1965.

M. Margoshes, Publicity Chairman, EAS 1964, attended

meetings of the Planning Committee, In September and

December, 1964,

International Union of Pure and Applied Chemistry.

B. F. Scrlbner, Titular member. Commission on Spectrochemlcal and Other Optical Procedures for Analysis.

71
Society for Applied Spectroscopy

M. Margoshes, Delegate, attended a meeting of the

Governing Board in October, 1964,

M. Margoshes, Chairman, Conference Committee, I965.

B. F. Scribner, Chairman of the SAS Advisory Committee,

presided at a meeting of the Committee in Pittsburgh,

Pa., March 2, 1965.

Spectrochimica Acta, Editorial Advisory Board

B. F. Scribner, member, attended a meeting of the

Editorial Advisory Board, at Pittsburgh, Pa.,

March 3, I965.

Washington Academy of Sciences

B. F. Scribner, Chairman, Auditing Committee, attended

meeting, December, 1964.

Members of the Section also serve on Division Committees,

for which several meetings were held during the year, and

on other assignments.

These are listed as follows:

NBS Analytical Chemistry Division,

Committee on Analytical Chemical Information.

B. F. Scribner (Chairman), K. F. J. Heinrich, and

M. Margoshes

Committee on Analytical Services

B. F. Scribner, and M. Margoshes

Committee on Standard Reference Materials

B. F. Scribner |

Division Newsletter

E. K. Hubbard

72
8. ACKNOWLEDGMENTS

The Spectrochemical Analysis Section has received

assistance from groups and individuals at NBS which has

aided our work in marked degree. While it is not feasible

to mention the many individuals involved we wish to express

our appreciation to all concerned for their contribution.

The NBS Procurement, Plant, and Shops Divisions have

been especially helpful in the purchase, installation, and

modification of new equipment, including the Electron Probe

Microanalyzer . The Electronic Instrumentation Section (of

the Measurement Engineering Division) through Louis

Marzetta has provided excellent service in the construction

of electronic devices.

In the Analytical Chemistry Division, the Radiochemical

Analysis Section through James R. DeVoe has provided advice

and assistance on electronic readout and computer

applications.

Robert E. Michaelis, formerly with our Section and now

with the NBS Office of Standard Reference Materials, has

been very helpful in consultation on the standards work of

the Section.

Two members of the Metallurgy Division, Harvey

Yakowitz and Donald L. Vieth have aided in providing

metallurgical services and in making measurements of

mutual interest with the Microprobe.

Our Section secretary, Mrs. Frances L. Hilten,

performs a wide variety of essential duties. It is a

pleasure to acknowledge her contributions to the work of

the Section and especially her assistance in preparing this

and other reports and in meeting critical typing deadlines.

73
9. LIST OF REFERENCES

[1] Margoshes, M., Excitation atid Ionization in Arc and

Spark Spectroscopic Sources, Appl. Spectry.

(Submitted)

[2] Margoshes, M.. and Scribner, B. F., Appl. Spectry. l8,

15^-5 (1964).

[ 3] Compilation of Chemical Compositions and Rupture

Strengths of Super-Strength Alloys, Am. Soc. Testing

Matls., Spec. Tech. Publ. 170-C (1964).

[4] Arrak, A., Spex Speaker 8, No. 3 (1963).

[5] Dilworth, H. C, Spectrochemical Analysis of HighTemperature Alloys by Spark Excitation in Argon

and Nitrogen, Amer. Soc. Testing Matls., Spec.

Tech. Publ. (in press),

[6] Brech, F,, and Cross, L., Xth Colloquium Spectroscopicum

Internationale, College Park, Md., 1962, Paper No.

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"~

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75


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