A UNITED STATES DEPARTMENT OF COMMERCE

PUBLICATION

Si. P

NBS TECHNICAL NOTE 494

3 ^4^ **

ARPA-NBS Program of Research

On High Temperature Materials

^IBHBBBBBBaa
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards ' was established by an act of Congress March 3, 1901. Today,

in addition to serving as the Nation's central measurement laboratory, the Bureau is a principal

focal point in the Federal Government for assuring maximum application of the physical and

engineering sciences to the advancement of technology in industry and commerce. To this end

the Bureau conducts research and provides central national services in four broad program

areas. These are: (1) basic measurements and standards, (2) materials measurements and

standards, (3) technological measurements and standards, and (4) transfer of technology.

The Bureau comprises the Institute for Basic Standards, the Institute for Materials Research, the

Institute for Applied Technology, the Center for Radiation Research, the Center for Computer

Sciences and Technology, and the Office for Information Programs.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United

States of a complete and consistent system of physical measurement; coordinates that system with measurement systems of other nations; and furnishes essential services leading to accurate and

uniform physical measurements throughout the Nation's scientific community, industry, and commerce. The Institute consists of an Office of Measurement Services and the following technical

divisions:Applied Mathematics—Electricity—Metrology—Mechanics—Heat—Atomic and Molecular Physics—Radio Physics '- —Radio Engineering -—Time and Frequency -—Astrophysics - —Cryogenics.

THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to im- proved methods of measurement standards, and data on the properties of well-characterized

materials needed by industry, commerce, educational institutions, and Government; develops,

produces, and distributes standard reference materials; relates the physical and chemical properties of materials to their behavior and their interaction with their environments; and provides

advisory and research services to other Government agencies. The Institute consists of an Office of Standard Reference Materials and the following divisions: Analytical Chemistry—Polymers—Metallurgy—Inorganic Materials—Physical Chemistry.

THE INSTITUTE FOR APPLIED TECHNOLOGY provides technical services to promote

the use of available technology and to facilitate technological innovation in industry and Government; cooperates with public and private organizations in the development of technological

standards, and test methodologies; and provides advisory and research services for Federal, state, and local government agencies. The Institute consists of the following technical divisions and

offices: Engineering Standards—Weights and Measures — Invention and Innovation — Vehicle Systems Research—Product Evaluation—Building Research—Instrument Shops—Measurement Engineering—Electronic Technology—Technical Analysis.

THE CENTER FOR RADIATION RESEARCH engages in research, measurement, and application of radiation to the solution of Bureau mission problems and the problems of other agencies and institutions. The Center consists of the following divisions: Reactor Radiation—Linac Radiation—Nuclear Radiation—Applied Radiation. THE CENTER FOR COMPUTER SCIENCES AND TECHNOLOGY conducts research and

provides technical services designed to aid Government agencies in the selection, acquisition,

and effective use of automatic data processing equipment; and serves as the principal focus

for the development of Federal standards for automatic data processing equipment, techniques,

and computer languages. The Center consists of the following offices and divisions: Information Processing Standards—Computer Information — Computer Services — Sys- tems Development—Information Processing Technology.

THE OFFICE FOR INFORMATION PROGRAMS promotes optimum dissemination and

accessibility of scientific information generated within NBS and other agencies of the Federal government; promotes the development of the National Standard Reference Data System and a system of information analysis centers dealing with the broader aspects of the National Measure- ment System, and provides appropriate services to ensure that the NBS staff has optimum accessibility to the scientific information of the world. The Office consists of the following

organizational units: Office of Standard Reference Data—Clearinghouse for Federal Scientific and Technical Information ' —Office of Technical Information and Publications—Library—Office of Public Information—Office of International Relations.

Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted; mailing address Washington, D.C 20234.

' Located at Boulder. Colorado 80302.

' Located at 5285 Port Royal Road. Springfield, Virginia 22151.
UNITED STATES DEPARTMENT OF COMMERCE

Maurice H. Stans, Secretary

NATIONAL BUREAU OF STANDARDS • Lewis M. Branscomb, Director

NBS TECHNICAL NOTE 494

ISSUED SEPTEMBER 1969

Nat. Bur. Stand. (U.S.), Tech. Note 494, 28 pages (Sept. 1969)

CODEN: NBTNA

ARPA-NBS Program of Research

on High Temperature Materials

Reporting Period

U 3u!y«3! December, 1968

Edited by A. D. Franklin

Institute for Materials Research

National Bureau of Standards

Washington, D.C. 20234

Supported by the

Advanced Research Projects Agency

of the Department of Defense

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 35 cents
CONTENTS

Page

1. Introduction -------------------- l

2. Objectives ------_-_-__--------- 2

3. Project Summaries ----------------- 6

3.1. Optical Constants of Titanium in the Visible

Region of the Spectrum

A. J. Melmed and J. J. Carroll ------- 6

3.2. Diffusion in Refractory Materials.

A. L. Dragoo ---------------- 6

3-3. Crystal Growth from Vapor

H. S. Parker and C. A. Harding ------- 7

3-^. High Temperature Creep in Metals

A. A. 0. Rukwied, W. A. Willard and

D. E. Harne ---_-__--_--_--_ 9

3.5. Deformation and Fracture of Ionic Crystals

S. M. Wiederhorn and L. H. Bolz ------ 14

3.6. Electronic Structure of Refractory Hard Metals

J. R. Cuthill, A. J. McAlister, L. H.

Bennett and I. D. Weisman __-____-_ 15

3.7. High Temperature Thermodynamics

E. D. West and S. Ishihara --------- 18

3.8. The Volatilization and Decomposition of

Materials

G. Mattamal, S. Straus, L. A. Dunlap and

L. A. Wall -__- ___ 22

3.9. Relaxations Near the Melting Point

J. P. Colson and R. K. Eby --------- 25
ARPA-NBS PROGRAM OF

RESEARCH ON HIGH TEMPERATURE MATERIALS

Work Performed at the National Bureau of Standards

Supported by the Advanced Research Projects Agency,

Department of Defense

Edited by

A. D. Franklin

Brief reviews are given of work performed

during the period July 1 to December 31, 1968,

on a number of projects concerning High Temperature Materials. Topics include the optical

constants of titanium, diffusion of oxygen in

oxides, growth of A^Oo bicrystals by chemical

vapor deposition, high temperature creep in

copper, fracture in glass, the electronic structure of transition metal borides and related

compounds, the enthalpy of pyrolytic graphite

at high temperatures, the mechanism of volatilization of polymers, and the interaction between

mechanical relaxation and annealing in polymers.

Key words: high temperature materials, materials

properties, mass transport, diffusion,

oxides, crystal growth, creep, copper,

fracture, glass band structure, transition metal borides, enthalpy,

pyrolytic graphite, evaporation,

mechanical relaxation and polymers.

1. INTRODUCTION

The National Bureau of Standards, with support from the

Advanced Research Projects Agency of the Department of

Defense, is carrying out a program of research on High Temperature Materials. In this program are included projects on

the properties of high temperature materials, projects on

their preparation, and others designed to explain the basic

phenomena limiting the use of materials at high temperatures.

A summary of the results achieved in the period is given here

1
2. OBJECTIVES

The failure at elevated temperatures of materials whose

properties are quite adequate at lower temperatures is one

of the important factors limiting the advance of Defense

technology. This fact has long been recognized and the

Department of Defense has in the past supported and is now

supporting a great deal of research to improve the highertemperature performance of a wide variety of materials

.

The continuing success of these efforts will depend upon timely advances of the science involved in materials preparation, characterization, and property control. It is the

overall objective of this program to identify some of the

more important of such key problems and to try to provide

the needed advances where NBS possesses the appropriate competence. Efforts will be directed mainly toward providing

techniques for the preparation and characterization of research materials, providing techniques for the measurement

of properties, obtaining reliable values of key pieces of

data, and improving the understanding of material behavior

particularly relevant to the higher-temperature performance.

In pursuit of this program, a continuing attempt is

being made to analyze technological problems in highertemperature materials use and distill from this analysis

major scientific problems whose solution would advance the

technology and to which NBS has the competence to address

itself. A committee has been formed to steer the work on

this analysis and to guide the program. While the analysis

is not yet at the stage of formal reporting, certain key

scientific problems of this kind have been identified and

are being worked upon. Examples are given below.

The corrosion, particularly by oxidation, of structural

metals at high temperatures Is an outstanding technological

problem. Protection by some sort of coating, either deliberately applied or formed as a passivating layer during the

initial stages of corrosion, is one well-explored approach

to solving the problem.

In the study of the initial phases of corrosion, ellipsometry is proving to be very important. To apply it adequately, however, the optical constants of the base metal

are needed. A project is described below (Optical Constants

of Titanium in the Visible Region of the Spectrum, A. J.

Melmed) aimed at obtaining these data for an important

structural material.
In the case of oxidation, the coating must provide a barrier to the passage of ions through the coating. Thus

diffusion in oxides is an important process, and this is

true also for a number of other technological problems, including sintering of ceramics, swelling of reactor fuels,

and operation of ceramic fuel cells. At present the diffusion of ions in oxides is not at all well understood nor

subject to anything but very crude control. Among the major

reasons are lack of sufficiently pure crystals upon which to

make measurements; the lack of reliable techniques for measuring diffusion rates, and therefore of reliable diffusion

data, particularly for oxygen diffusion; and the lack of

well-characterized grain boundaries to assess the importance

of intergranular diffusion in polycrystalline ceramics and

oxide films

.

Several projects in this Program are concerned with

studies related to these areas. Continued assistance is

being given to ARPA in the scientific surveillance of a group of projects supported in other institutions by ARPA

and aimed at producing oxide crystals worthy of diffusion

research and at developing techniques and reliable data on

diffusion in oxides. At NBS , in this present program,

efforts are being made at developing a technique for the

reliable determination of oxygen diffusion coefficients

(Diffusion in Refractory Materials, A. L. Dragoo) and for

the growing of oxide crystals, particularly with controlled

grain boundaries, by chemical vapor deposition (Crystal

Growth from Vapor, H. S. Parker and C. A. Harding).

Several other mechanisms operate to degrade the mechanical properties of structural metals and non-metals at higher temperatures. Creep becomes a problem in all metals at

sufficiently high temperatures, but the mechanisms involved

are not well understood, particularly the roles played by

dislocation motion and self-diffusion for the very slowest

deformation processes. A project in this field (High Temperature Creep in Metals, A. A. 0. Rukwied) is concentrating

on copper as a model material at the present time.

Ceramics would have great potential as structural high

temperature materials but for their tendency to brittle

fracture. Crack initiation and propagation processes are

important. There is often chemical reaction with the environment involved, leading to stress-corrosion. Techniques

are needed for studying these processes In a detailed way,

to enable the role of plastic deformation, crystal orientation, surface energy, chemical reactions, and other contributing processes and parameters to be spelled out. The

3
Project in this area (Deformation and Fracture of Ionic

Crystals, S. M. Wiederhorn) has developed a very refined

technique of this kind for the study of crack propagation

and is using it for fracture studies in inorganic glasses,

oxides such as AlpCU, and will perhaps include grain boundary fracture in AlpOo if bicrystals become available.

A class of high-temperature materials that have very

useful properties but that have not received as much attention as, e.g., the refractory metals and the oxides, is that

of the electron-rich intermetallic compounds, such as the

transition-metal carbides. The electron states are very

important in determining the physical as well as electronic

properties of these materials. These electron states are

summarized in the electronic band structure, and progress

has been made in both the theoretical calculation and experimental probing of such band structures. A project (Electronic Structure of Refractory Hard Metals, J. R. Cuthill,

A. J. McAlister, L. H. Bennett and I. D. Weisman) in this

area is capitalizing upon the very high-resolution NBS softx-ray emission facility combined with related measurements

(nuclear magnetic resonance and Mossbauer spectrometry) to

elucidate the band structures of transition metal borides

and beryllides.

Graphite represents another class of high-temperature

materials. There had been a report (from proprietary

sources) that pyrolytic graphite exhibits high-temperature

thermodynamic properties quite different from those of wellcrystallized graphite. If true, the comparison could help

shed light on the structure and properties of pyrolytic

graphite. In a Project just completed (High Temperature

Thermodynamics, E. D. West and S. Ishihara) a unique NBS

high temperature calorimetry facility was used to show that

no significant difference exists between the enthalpies of

pyrolytic and well-crystallized graphites at high temperatures . While polymers are not thought of as high-temperature

materials in the same sense as ceramics, their use is

limited to temperatures below a certain upper limit. In the

neighborhood of and above this limit, there are "high-temperature problems" in polymers. One of these is the evaporation of polymers, used as coatings, sealants, elastomers,

lubricants, etc., in vacuum environments. To control and

improve the behavior of polymers in this respect, the process must be understood. A project in this area (The Volatilization and Decomposition of Materials, G. Mattamal,

S. Straus, L. A. Dunlap, and L. A. Wall) is aimed at sepa-
rating the process of evaporation by molecular units from

that of degradation of the molecules followed by evaporation of the fragments in model materials, and at studying

the vaporization of plasticizer components.

By maintaining a continuing analysis of important needs

in the science underlying high-temperature use of materials,

and matching problems to NBS competence, it should be possible to have a dynamic, evolving program that contributes

significantly to solving current and future high-temperature

problems, and can also act as a source of assistance and

advice to ARPA in this important field.
3. PROJECT SUMMARIES

3.1. Optical Constants of Titanium in the

Visible Region of the Spectrum

A. J. Melmed and J. J. Carroll

Metallurgy Division

Institute for Materials Research

The purpose of this project is to measure optical constants (complex index of refraction) in the visible light

spectrum for clean titanium surfaces in ultra-high vacuum,

using the technique of ellipsometry . Since Ti is an hepstructured metal it is expected that optical properties will

vary with surface crystallographic orientation. Therefore

single crystal as well as polycrystal specimens will be investigated . Some ( 0001) -oriented single crystal specimens were prepared and optical constants were measured in ambient air.

We are awaiting construction of a new ellipsometry-LEED tube

in order to proceed with the planned ultra-high vacuum measurements. Because a prospective employee, counted upon for

the major portion of this project, elected not to join the

NBS staff, progress on this project has not been as rapid as

planned.

3.2. Diffusion in Refractory Materials

A. L. Dragoo

Inorganic Materials Division

Institute for Materials Research

The objectives of this program are to measure and to

interpret diffusion of oxygen in single crystal oxides.

Experimentally these two objectives consist of (1) extending the sensitivity of present techniques so that the 0^°

distribution in a single crystal sample can be measured,

(2) comparing the results of these concentration profile

measurements with measurements of the rate of exchange of

1 " between the gas phase and the oxide crystal, (3) determining the dependence of the diffusion rate on temperature,

oxygen partial pressure, impurities in the solid, etc. and

(4) obtaining reliable diffusion and exchange coefficients.

In regard to interpretation, this objective translates into

determining the mechanisms for oxide ion diffusion in the
oxide studied. Currently, rutile (TiOo) is the oxide of

interest. A mass spectrometer is being used to determine

isotope ratios.

To date, the research has been concerned principally

with developing an analytical technique for determining the

0^° content of small (~lug) samples of oxide. AgCN reduction to produce CO2 has been discarded because yields were

too low. Presently, a graphite reduction chamber is being

set up to liberate the oxygen as CO. This appears to be

both kinetically and thermodynamically feasible above l800°C

if a platinum catalyst is used. Since CO2 is more desirable

than CO for mass spectrometric analysis, the conversion of

CO to COp at a hot filament is being studied. Several different metals are being tested.

The diffusion equation was solved for a problem involving competition between two different solid diffusion media

for the isotope in the gas phase. This problem arose out of

the need to separate the effects of the sample and of a partially O^-enriched alumina furnace tube. The problem was

solved assuming equilibrium with the gas at the surfaces of

both materials, a continuous initial distribution in the

walls of the tube and an initially normal 0^° content

throughout the solid. It appears to be possible to extend

the mathematical procedure to problems of a finite rate of

exchange

.

3.3* Crystal Growth From Vapor

H. S. Parker and C. A. Harding

Inorganic Materials Division

Institute for Materials Research

The objectives of this program are to obtain an understanding of the parameters controlling perfection, purity,

and dopant distribution in single crystals prepared by the

vapor growth technique and to extend the technique to a wider range of refractory oxide materials. Specifically, it

is planned to investigate the effect of process variables

such as partial pressures of reactants, total pressure, and

growth temperature on the growth process and to utilize this

information to further develop the technique for the growth

of well-characterized research materials of greater physical

perfection and chemical purity. Aluminum oxide has been

chosen as the first experimental material because previous
work by other investigators has shown the suitability of the

vapor growth technique for AI2O0 and because of its technological importance and scientific interest as a research

material

.

During this reporting period, emphasis has been placed

on the growth of AI2O3 bicrystals containing tilt boundaries.

Results have been encouraging. Thus far, bicrystals have

been grown with either 15° or 30° tilt misorientations between the c-axes in the mirror plane (i.e., rotation about

an a-axis). The maximum size of bicrystal obtained thus far

is of the order of 3 x 5 x 20 mm during a growth period of

24 hours. Attempts to extend the growth period have been

unsuccessful thus far, because of secondary nucleation on

the growing faces and departure of the boundary from the desired propagation direction. The possibility of grinding

and repolishing the crystal at intervals during the growth

cycle to overcome the secondary nucleation is being investigated. The problem of maintaining the growth of the boundary

in the desired direction, particularly in the case of the

30° misorientation, is more critical and may represent a limitation on the maximum size which can be grown, at least

in this particular orientation. Preliminary optical and

x-ray examination of the 30° specimens indicate that the

favored propagation direction may be a (44B"3) plane. Microscopic examination indicates the boundaries to be of good

quality, free of inclusions or porosity.

As anticipated, the perfection of the seed crystals has

a marked influence on the perfection of the resulting bicrystal. The use of Verneuil boules has been abandoned in

favor of Czochralski-grown ruby as a source of seed plates.

No trouble has been experienced with diffusion of chromium

from the seed into the growth regions. The use of vapor

grown crystals for seed plates is also being investigated.

Reaction of AlClo vapor with the nickel-alloy injector

on the growth chamber is felt to be a possible source of

contamination in the crystals as evidenced by deposits on

the inner surface of the chamber. The use of an inner AI2O3

tube to minimize this effect is currently being evaluated

but the results of chemical analysis are not yet available.

During the next reporting period, it is planned to

complete the characterization of the bicrystals and to submit a paper for publication summarizing the results of the

growth of bicrystals of Al

2 0o by the vapor growth technique.

8
3.4. High Temperature Creep in Metals

A. A. 0. Rukwied, W. A. Willard, and D. E. Harne

Metallurgy Division

Institute for Materials Research

Obj ectives : The objectives of this project are to investigate the

microscopic mechanisms that control high temperature creep,

i.e., creep occurring at temperatures T> Tm

/2, where T is

the melting point. More specifically it is planned to study:

(a) the effect of temperature on creep rate and compare

this to the temperature dependence of dislocation

velocity,

(b) the effect of stress and compare this to measurements of dislocation density carried out by etch

pit techniques,

(c) study the effect of stacking fault energy through

its variation in an alloy series and

(d) study the effect of grain boundaries by comparison

of studies in single crystals and polycrystals

Equipment :

A commercial Baldwin creep machine has been equipped

with a high temperature furnace, using an inert gas, Helium,

which is being highly purified by a system containing a cryosorb trap. This machine provides data for complete

creep curves and has provision for stress and temperature

cycling, the latter at relatively slow rates only.

Additional testing equipment has been designed and built

in a joint effort with SATEC SYSTEMS, Inc., to conduct creep

tests on single crystals at constant resolved shear stress

as well as on polycrystals at constant true stress or even

at constant load in high vacuum (10"^ - 10"° N/m2 ) or at any

intermediate pressure of inert gas between atmospheric

pressure and high vacuum. The machine is capable of performing the rapid temperature and stress changes needed for

activation analysis.
The control of the resolved shear stress is accomplished

by the use of an analog computer, which calculates the resolved shear stress signal from the extensometer and load

cell signals. This signal is compared with a set stress

signal in a PAT control unit and the error signal is used

to control the pneumatic load on the specimen. This setup

is also capable of conducting tests at constant resolved

shear strain rate or any stress rate. This equipment has

been transferred to and accepted by NBS

.

Experimental Work

Creep tests on polycrystalline copper

Using the Baldwin creep machine, work has been concentrated on the temperature dependence of high temperature

creep in first and second stages at three stress levels

(a=10.34, 15.51, and 20.68 M N/m2

, or 1500, 2250 and 3000 psi)

.

First stage creep

The analysis of first stage creep confirmed the existence of a power law, relating strain, e, to time, t, in the

form

e = e (T) + g (T) t

m

,

' (1)

where e (T) is the instantaneous strain upon loading at the

thermodynamic temperature T, g(T) is a constant for fixed

temperature and stress, and the number m is the time exponent. Relationship (1) was found to be valid up to about

4 min at the highest temperatures and up to about 50 hr at

the lowest temperatures tested.

The time exponent, m, was found to be 1/2 for the very

first portions of the creep curves at all temperatures and

stresses tested. For copper, a value of m=l/3 has been reported in the literature. In the present measurements that

exponent does not hold at the beginning of the creep curves,

but is valid at some time interval subsequent to that one

described by m=l/2.

The instantaneous strain, e (T), measured by extrapolating the straight lines of e vs . t^/ 2 £o t=0 increases very

slightly with increasing deformation temperature from 525°

to 6l0°C at a stress of 10.34 M N/m2 . However, from 610° to

692°C a very strong increase of £ (T) with deformation temperature was observed, suggesting that a diffusion controlled

process governs the instantaneous strain on loading at the

higher temperatures, i.e.

10
e (T) cc f(exp(-U /kT)) . (2)

£ o However a value for the apparent activation energy cannot be

derived from the measurements since the exact functional relationship between strain and temperature is not known. At

the higher stresses tested, only a weak temperature dependence of e (T) was found within the workable ranges of temperature. Preliminary tests at a stress of 6.89 M N/m2 (1000

psi) ran into difficulties due to partial recrystallization

occurring at the beginning of the tests.

The quantity 3(T) is strongly temperature dependent.

Assuming a thermally activated process underlying first

stage creep, an approach can be made starting from an

Arrhenius equation for the strain rate

e = e Q exp (-U^/kT) (3)

and combining it with the empirical equation (1) differentiated with respect to time

e = m $CT) . t"

1 "" 1 (la)

= 6(T) / 2.t 1/2 for m=l/2 (lb)

which results in

ln(gCT)/2.t 1/2 )=-U

I

/kT + const . (4)

Assuming that at constant stress at various temperatures at

the respective end points of the range of validity of eq. (1) a homologous structure

Q

in the material is reached, the respective creep rates, Eggs can be calculated from eq. (lb)

using the experimental values of $(T) and the creep strains,

egg, at the end of the 3-ranges in order to derive an apparent activation energy from eq. (4). At all stresses tested,

this evaluation resulted in an apparent activation energy

value close to that for self diffusion.

These results are confirmed by graphing in an Arrhenius

type plot the time, tg E , needed to creep a sample to the

strain, egg- These results give an activation energy for

self diffusion at test stresses of 10. 34 and 15-51 M N/m2

(1500 and 2250 psi) for both time exponents, m=l/2 and m=l/3.

Second stage creep

One of the major objectives to date of the test series

was to find the temperature interval in which, according to

reports in the literature, the activation energy for steady

11
state creep rises from some lower value to that one for self

diffusion. However, within the capability of the Baldwin

creep mahine and with reasonably long creep tests, an activation energy which is somewhat less than the one for self

diffusion (about 184 kJ/mol [44 kcal/mol]) was measured from

the steady state creep rates in the two lower stress series.

This seems to be true also for the series tested at 20.68

M N/m2 (3000 psi). The cause for this difference can be

attributed to the use of different purity copper, different

inert atmosphere, (slightly) different grain size, and different loading conditions.

Prom the time needed to creep specimens through the

second stage at both stresses, 10.34 and 15-51 M N/m2

(1500 and 2250 psi), the activation energy for self diffusion could be derived.

The time to creep specimens to fracture or onset of

recrystallization at the higher temperatures shows an interesting break at cr=51.51 M N/m2 (2250 psi). From the

temperature interval between 440° and 505°C the activation

energy for self diffusion was derived. Between 525° and

562°C, however, one finds an apparent activation energy

which comes closer to the one for recrystallization. Since

in this higher temperature interval the strain is proportional to tl/3 until fracture, it seems that the specimen

are never crept beyond state I and that they recrystallize

,

once enough energy is stored in stage I deformation. At

the lower temperatures the specimen fracture is not due to

recrystallization but is due to a process governed by self

diffusion. Comparison between the stress levels at a=10.35

and 20.68 M N/m2 (1500 and 3000 psi) shows, that the former

leads to the activation energy for self diffusion, while

the latter thus far seems to tend more to the value for recrystallization. This observation seems to be important

with regard to the definition of stage II.

Creep of single crystalline copper

Since the SATEC testing equipment has been accepted

only recently, no results are available at this time. Since

crystalline test specimens of specified orientation are on

order from a commercial company. Delivery of these specimens is nearly completed. Furthermore, techniques for profiling straight cylindrical single crystals into buttonhead

specimens have been explored.

12
Study of growth structure in test material

Etch pit studies aimed at measuring the dislocation

density in the polycrystalline copper under various conditions of creep, encountered difficulties in continuously

cast material in that a substructure was found which probably is due to segregation of impurities during freezing

of the metal from the melt. This substructure cannot be

destroyed by cold working and subsequent annealing treatment

unless the temperature is raised very close to the melting

point (T y 1050°C). A closer investigation of this phenomenon with help of transmission electron microscopy, electron

and ion probe microanalysis is under way. The purity of the

material has been re-checked by several types of analyses

and found to be in the range of 99-99% to 99-999% Cu before

and after testing.

There are extensive reports in the literature on cellular growth in alloys, however, a second constituent is usually present at a much higher concentration than 1 to 10 ppm

The cell walls are reported to consist of an enrichment of

the second constituent, second phase particles or even massive precipitation of a second phase depending on the concentration and the solubility of the second constituent in the

matrix. In addition dislocation networks have been observed

which apparently are needed to accommodate the second constituent. In our metal, the electron probe could not detect

any foreign atoms within that substructure. An ion probe

thus far produced an integral analysis of the specimen surface which resulted in the detection of 3 ppm carbon, in

good agreement with a chemical anlysis (3-5 ppm C). Transmission electron microscopy however did detect dislocation

arrangements, the locations of which are in agreement with

the optically observed phenomenon, but so far no second

phase particles could be seen.

The transmission electron microscopy work was done In

collaboration with Dr. A. W. Ruff, NBS

.

13
3.5- Deformation and Fracture of Ionic Crystals

S. M. Wiederhorn and L. H. Bolz

Inorganic Materials Division

Institute for Materials Research

The objective of this program is to study and understand the fracture processes in ceramic refractories and to

determine the effect of plastic deformation and environment

on fracture. Fracture mechanics techniques are being used

in this study to determine fracture surface energies, parameters that give precise measurement of resistance to splitting. Experiments are being conducted on glass because of its

commercial importance and because it serves as a model material for brittle failure. Research on glass has two

goals: one, a determination of the inherent resistance of

glass to fracture and two, a determination of environmental

effects on fracture.

During the last six months, the stress-corrosion reaction of water on six glass compositions was studied. Crack

velocity data was obtained in liquid water as a function of

temperature and applied load. The data obtained satisfies

the Charles-Hillig theory which assumes that stress-corrosion

is due to a stress-enhanced chemical reaction at the crack

tip. Apparent activation energies for the stress-corrosion

reaction were 138 kJ/mol (33.0 kcal/mol) for fused-silica,

128 kJ/mol (30.7 kcal/mol) for boro-silicate glass, 121 kJ/mol

(29-0 kcal/mol) for aluminosilicate glass, 106 kJ/mol (25.3

kcal/mol) for soda-lime glass, and 105 kJ/mol (25.2 kcal/mol)

for lead-alkali glass. These data are being analyzed in

hopes of establishing the particular chemical reactions controlling crack propagation in glass. It is interesting that

the lowest two activation energies were obtained on glasses

that contained large amounts of alkali ion, suggesting an

important role for these ions in the stress-corrosion reaction.

Paper Published During Report Period

S. M. Wiederhorn, "Moisture Assisted Crack Growth in

Ceramics", International Journal Fracture Mechanics _4,

171-7 (1968).

1H
3.6. Electronic Structure of Refractory Hard Metals

J. R. Cuthill, A. J. McAlister, L. H. Bennett, I. D. Weisman

Metallurgy Division

Institute for Materials Research

The objective of this project is to study relationships

in the changing density of states upon compound formation in

refractory hard intermetallic binary compounds. Such information is expected to contribute to the understanding of

basic relationships useful for the design of high temperature

alloys with prescribed properties.

Measurements will be made which give information on

aspects of the electronic structure, such as density of

states and internal magnetic and electric fields as a function of temperature, important to an understanding of bonding

and the physical properties of refractory hard binary intermetallic compounds. The representative class of compounds

are those which exhibit metallic character and are characterized by one constituent element having an incomplete dor f-shell and the other constituent element having no dor f-electrons. The various series of borides, aluminides,

beryllides, and silicides of the metals of the first and

second transition series are compounds of the above type.

Compounds to be included in the experimental program will be

selected from those meeting the above criteria, on the basis

of the possibility of obtaining we 11 -characterized samples.

Soft x-ray (valence band) spectra will be obtained from the

compounds as a function of temperature. The emission spectrum

is related to the density of occupied states in the valence

band. Corroborative information on internal magnetic and

electric fields and the shape of the density of states at the

Fermi energy will be obtained from NMR, Mossbauer, magnetic

susceptibility, and electronic specific heat measurements.

The efforts thus far have been in four categories:

(1) Preparation of transition metal-borides ; (2) Properties

of transition metal-borides; (3) Properties of transition

metal-beryllides ; (4) Properties of transition metal-aluminides. Each of these is discussed in turn.

(1) Preparation of transition metal-borides. Attempts,

reported previously, to prepare specimens by various melting

procedures were largely unsuccessful. However, acceptable

material in powder form of the following borides, as revealed

by metallography, x-ray diffraction, and character of the

15
NMR spectra, has been obtained from commercial sources for:

TiB 2

, VB 2

, Cr^B^, CrB, CrB

2

, Fe 2 B, NbB, and CoB. Having

examined the powders in this manner, some of the same material of those found acceptable have been returned to the producer to fabricate rod-shaped specimens for soft x-ray spectroscopy .

(2) Properties of transition metal-borides

.

(a) Preliminary soft x-ray spectra were obtained

on the only samples available, the initial

arc-melted VB, CrB, PeB, and Ni~,B. Good intensities in the transition metal spectra were

obtained (good boron spectra were obtained and

reported earlier). Useful results should be

possible as soon as good specimens are obtained.

Significant variations in spectral shape, width,

and peak energy between the elemental and combined form of the constituent were noted.

(b) Preliminary Knight shift determinations on both

the boron and the transition metals were made

on most of these borides. The boron Knight

shifts in both the monoborides and diborides are

of the order of 0.1$ or less. The transition

metal Knight shifts in these borides are significantly larger, but are still below 1%

.

(c) The hyperfine magnetic fields and quadrupole

interactions in FepB were studied in our laboratory and have been reported on. 57Fe

Mossbauer spectra and both the c.w. and pulsed

NMR of the llB in the 4.2 to 373 K temperature

range were determined. NMR frequency dependence upon pressure of -^B in Fe^B was recorded

up to 680 M N/m2 (6.8 k bar). The frequency

dependence upon temperature was found to deviate from the expected T3/2 relationship below

104 K. This deviation is explained on the

basis of a spin wave gap arising from the magnetocrystalline anisotropy and Lorentz fields.

(3) Properties of transition metal-beryllides

.

(provided gratis by the Brush Beryllium Company)

A number of beryllides in addition to those reported earlier,

namely ZrBe 2

, MnBe 8

, FeBe 11 , NbBe., ZrBe.o, CrBe 2

, TiBen 2

, VBe 12 , WBe 2

, and WBe 12 have been examined in our laboratory

and found to be nonmagnetic and nonsuperconducting above 1.4 K.

16
(4) Properties of transition metal-aluminides . An

improved NMR pulse echo technique was developed in our laboratory and applied to the study of the distribution of

electric field gradients at the various nuclear sites in

NiAl. NiAl has the cubic cesium chloride structure but although the phase is stable over a wide range of stoichiometry, there are deviations from cubic symmetry associated with

departures from the equiatomic ratio. This deviation from

cubic symmetry introduces a distribution of electric field

gradients at the various nuclear sites. The NMR pulse-echo

technique is a unique method for getting information on the

distribution of these field gradients. In the present work,

a variation of the technique was developed and shown theoretically and experimentally to enhance the spin echo pattern

by a factor of 5 over what had been achieved previously.

Preliminary data on the quadrupole distribution at the Al

sites was obtained. Also, soft x-ray spectra have been obtained from NiAl which have been included in a paper published in the Journal of Applied Physics.

Papers Published in the Course of This Research

1. Resonance Studies in Ferromagnetic Pe^B and Fe^Zr, I. D.

Weisman, L. J. Swart zendruber , and L. H. Bennett, presented at the 1968 Conference on Magnetism and Magnetic

Materials, New York, N.Y., November 1968, and to be published in the Physical Review.

2. Perromagnetism in CrBe 1? , N. M. Wolcott and R. L. Falge,

Jr., Phys. Rev. 171, 591 (1968).

3. Nuclear Magnetic Resonance Studies in Paramagnetic and

Ferromagnetic CrBe.p, N. M. Wolcott, R. L. Falge, Jr.,

L. H. Bennett, and R. E. Watson, Phys. Rev. Letters 21 , 546 (1968).

4. Magnetic Behavior of Intermetallic Compounds of Beryllium, N. M. Wolcott, R. L. Falge, Jr., and L. H. Bennett,

presented at the 1968 Conference on Magnetism and Magnetic Materials, New York, N.Y., November, 1968, and to

be published in Journal of Applied Physics.

5. Quadrupole Echoes in Solids, I. D. Weisman and L. H.

Bennett, to be published in the Physical Review.

6. Soft X-Ray Spectroscopy of Alloys: TiNi and the Ni-Al

System, J. R. Cuthill, A. J. McAlister, and M. L.

Williams, J. Appl. Phys. 39, 2204 (1968).

17
3.7. High Temperature Thermodynamics

E. D. West and S. Ishihara

Heat Division

Institute for Basic Standards

Measurements of the enthalpy of pyrolytic graphite at

high temperatures were undertaken because there are no published data for this material and the proprietary information

available indicated large differences from other graphites.

If these differences were real, they would be of considerable

scientific interest; if not, the engineering data need to be

corrected.

The experimental work has been completed. Twenty-three

experiments were carried out with pyrolytic graphite and six

direct comparison experiments were carried out with spectroscopic grade CCH graphite. No significant differences were

observed, so all data were fit by method of least squares to

obtain the equation

HT"H 2Q8 15

= A£n(T)+BT+CT 2 / 2 +D k J/mol (1)

where

A = -5.77540

B = 2.59895 x lO- 2

C = 1.23817 x 10-6

D = 25.1021

Estimated standard error = ± .093%

The estimated standard deviation is 0.09%, where the

estimated standard deviation, s, is given in terms of the

differences, r, between the equation and the observed values,

the number of experiments, n, and the number of constants

(4) in equation (1)

.

s == Jl r 2/(n-4)

This precision sets a very small upper limit on possible

differences between pyrolytic graphite and spectrographic

grade graphite.

18
The experimental data are presented in the table. In

the first column are the furnace temperature and the dates

of the experiment. The chronology of the experiments was

planned to be random in order to uncover any systematic

error associated with aging of the furnace or other parts

of the apparatus. Randomness was lost for some of the highest temperatures when some of these experiments were repeated to eliminate a small systematic error due to the insufficient furnace warm-up time before taking data.

In the second column, the enthalpy data are given,

corrected for the small difference between the final calorimeter temperature and 298. 15 K. In the third column the

moles of graphite in the sample are given along with the

designation of the type of graphite. The weights of samples

decrease slightly with time, probably due to abrasion in

handling.

In the fourth column, the observations are converted to

enthalpy per gram atomic weight of graphite and in the fifth

column are given the percent differences between the observations and eq. (1).

The graphite specimens were analyzed spectroscopically

for the metals.* The largest impurity was copper, which was

less than 0.01$. Iron, which was found to be less than

0.005% in an unused pyrolytic graphite sample was not deteced in the sample used. Titanium, which was not found in the

unused sample, was less than 0.005% in the samples used.

The original impurities and the contamination in use are

therefore considered negligible. The enthalpy was not corrected for impurities.

The enthalpy of pyrolytic graphite does not differ by

as much as 0.1% from the enthalpy of spectroscopic grade

graphite. The enthalpy calculated from eq. (1) agrees with

the equation obtained in the previous measurement [1], made

by somewhat less accurate techniques, to 0.1% at 1200 K and

going up to 1.3% at 2500 K. Observations which report such

differences should be examined carefully for the adequacy

of the method.

[1] E. D. West and S. Ishihara, Advances in Thermophysical Properties at Extreme Temperatures , "A

Calorimetric Determination of the Enthalpy of

Graphite from 1200 to 2600 K", ASME, 1965, pp.

146-151.

*Analyses were carried out by Mrs. M. M. Carr of the

Spectrochemical Analysis Section.

19
Enthalpy of Pyrolytic and Spectroscopic Graphites

Furnace

Temp K

and Date

Heat to

Calorimeter

at 298.15 K

Gram-atoms C;

Specimen

H -H _ T 298.15

J/gaw

% Above

Equation

1174.3

6-5-68

7140.8 J

2364.8

2364.8

7140.9

.305408

.305405

A*

A

15638

15639

- .09

- .09

1199.6

4-1-68

2349.9

7305.9

6913.4

2350.2

.305412

.281312

A

B*

16227

16221

.02

- .02

1299.8

4-3-68

2676.5

7892.3

8339.5

2677.3

.281309

.305412

B

A

18541

18540

.12

.11

1400.1

3-28-68

3009.4

9387.3

8881.7

3007.9

.305413

.281316

A

B

20883

20880

.09

.07

1499.4

4-15-68

3330.3

10426.2 .305412 A 23234 .03

1499.6

4-17-68

3332.5

10421.6

10432.2

3334.6

.305412

.305412

A

A

23212

23240

- .09

.03

1602.8

4-10-68

11530.3

3681.0

3681.8

11546.7

.305410

.305409

A

A

25701

25752

- .11

.09

1604.7

7-8-68

11780.8

3912.8

.305408 A 25762 - .05

1699.8

3-15.68

11905.2

4009-5

4011.0

12605.6

.281317

.305420

B

A

28067

28140

- .15

.11

20
Enthalpy of Pyrolytic and Spectroscopic Graphites

Furnace

Temp K

and Date

Heat to

Calorimeter

at 298.15 K

Gram-atoms C;

Specimen

H

T"

H 298.15

J/gaw

% Above

Equation

1700.1

3-13-68

12601.4 J

4018.3

.305420 A 28102 - .05

1899.7

3-11-68

4669.4

14779.6

14780.6

4675.6

.305416

.305416

A

A

33103

33086

- .01

- .06

2001.8

4-12-68

5022.2

15912.0 .305409 A 35656 - .14

2104.4

3-21-68

5391.6

16197.0 .281322 B 38409 .17

2202.1

7-23-68

5981.9

18384.9

18384.2

5979.1

.303372

.303372

A

A

40884

40891 .02

2202.2

7-10-68

5986.6

18485.4 .305407 A 40925 .10

2302.8

8-12-58

6332.2

19002.0

19002.1

6346.4

.290982

.290979

A

A

43541

43494

.05

- .06

2398.5

7-31-68

6705.0

20659.0

20665.0

6705.7

.303338

.303338

A

A

46002

46019

- .11

- .07

2494.1

8-6-68

7062.7

20311.6 .272305 B 48655 .11

'Specimen A is pyrolytic graphite; B is spectroscopic grade

21
3.8. The Volatilization and Decomposition of Materials

G. Mattamal, S. Straus, L. A. Dunlap, and L. A. Wall

Polymers Division

Institute for Materials Research

The overall objective of this project has been to better

understand the mechanism of the molecular vaporization of

large organic molecules from the liquid state and particular

to investigate or determine the size at which thermal decomposition is required for volatilization to occur. Our initial studies include investigation of linear alkanes and a summary of our results is shown in Table 1.

Table 1. Activation Energy for Vaporization of

Linear Alkanes, H(CHp)

nH

e j kJ/mol

19 268

24 338

36 506

94 1318

Sol Para

Eq. (2)

88

111

165

456

Theory Exp

MW Eq. (2) Eq. (1) Exp.

79 84

91 92

120 117

229 209

Here we list the experimental activation energies, e , for

vaporization and compare them with values calculated from

enthalpies of vaporization, which in turn were obtained with

the equation:

AH = 13.4 n 2/3 - 0.0807 T + 12.2 (1)

in which T is the temperature in kelvin and n the chain

length.

This relationship, or more specifically the term with

n 2 /3, results from the theoretical model that flexible molecules vaporize as compact spheres. The numerical coefficients in the expression were determined by fitting the

relation to available data in the literature. The activation energies were obtained from the enthalpies with

e„ = AH - 1 RT = AE„ - 51 . v v 2 v 2

22
We also make a comparison in Table 1 with activation

energies calculated from estimated solubility parameters.

Since the solubility parameter,

AE . V\ 1/2

6 = C-yl)

then

S - « 2v - 5| . (2)

Values calculated in this manner show an increasing

deviation from the experimental value with the size of the

molecules, i.e., n or MW, and indicates that the solubility

parameter is not related to the actual energy of vaporization but to the maximum energy of vaporization, i.e., to the

energy for the hypothetical vaporization of an extended

chain. It immediately follows that the difference in the

energy determined from the solubility property and that

determined from the rate of vaporization is the energy for

extending the chain in a vacuum.

The rates of vaporization of twenty-one commercial

plasticizers were also measured. From the volatilization

kinetics it was determined that eleven plasticizers were

essentially pure compounds. Activation energies for vaporization for these were determined and compared to those

calculated from solubility parameters (Eq. 2). These results were described in detail at the 156th National Am.

Chem. Soc . Meeting, September 1968.

Since September, a series of related phenylene ether

compounds have been studied. Preliminary results are shown

in Table 2. These compounds are of interest as thermally

stable liquids and polymers. The first group of substances

listed are the meta-linked polyphenylene ethers, 3 to 7

phenylene rings. In this range the activation energy appears

to be linear. The largest species (7 rings) is being purified and its activation energy for vaporization redetermined,

since its listed value shows the beginning of a deviation

from linearity with molecular size. The last two compounds

show a 29 kJ (7 kcal) difference between the activation

energy for two isomers. This is a 44% increase on going

from an ortho to a para isomer, and shows the effect of

molecular structure independent of molecular weight.

FUTURE PLANS

(1) Extend our vaporization studies to include the

available series of glycerides (tributyrin to tristearin)

23
co

•HP

cti ta •H

Sho

a,

cd >

Shcd Ho

CD rHOO

Ch

racd •HhO

Sh

(UCHCO

•H

-P

cd>

•HPO<

CM

CD H

£1

cd Eh

cd pC

(DB

•H

CD&x

CD> OB\i—i

cdooB\

cd rH36

ShO

ft

T5Coboo

T3

CD

•HS

!h

CD P

CD T5

CD X!OP

CMm

CM VO

CM o

CM CM CM

co

-=r

i_n oo

CMo

MO

CMonmmo

-=r vo co o

u~\ -3- oo en

on -=r i_n vo

LO. LD, in un Ln

ffi ffi HH

m ix{ VO VO VO vo vo O o o o o

CM

m ^d- Ln vo

-1-* '-h '-h '-h "-h O O O o o

^r ^r ^r ^r ^3- X! |x! W K W

VD vo vo vo vo O o o o o

<^ -4^ ^hv M' <HV

ffi |x!

W

u

CD XIp

!x|

CDG

CDNc

CD X3

CD CD I—I £ i—i

>a

CD rH

X

to >J

O

C c g

CD CD CD

!h X) X! x:

CD Oh Ch

x: ^^ •—-s *~N p >3 >> >5

CD

XX

X

,"-n o o o

rH c £ £

CD >S CD CD 0) G C £ x: XI

CD CD

a

a Oh

N X! c Oh >> >s >5

CD

XXX

X> >5 o o o X G £ £

>aO CD

X

C x; x: x; o CD a a Oh c £ i i ^^

CD Ph

B

B

B

X! 1 v_^ ^^ L_J P, S CO S CO •H *«-^ •H i i •H 1

CO •H xai

CO •H

O1 B X3 S X3 B

on

CM

vo

OAm

vo

vo

vo

on

vo

CM CM

Ln Ln X K

vo vo o o o o ^3- ^d- W W

vo vo o o

Ln Ln W K

vo vo o o

inU

CD 0) x: x; p p

CD <L> rH H

>i >i c £

CD CD XI x;

Oh

a

H rH >3 >3 H H

>> >3 £ SH CD CD Xh x; Oh p.

•H •H o1 O1 CM

24
which can be considered to be linear molecules with a branch

at the centers and the series of linear sebacate esters

(dibutyl sebacate to dioctadecylsebacate )

.

(2) Extend our vaporization studies of these compounds

to include measurements of their vaporization from amorphous

polymers and hence to measure vaporization controlled by the

diffusion process as well as that controlled by the molecular vaporization process.

(3) If time permits to explore the effect of solubility

or compatibility of the plasticizer with the polymer on the

rate of vaporization.

PUBLICATIONS ON THIS PROJECT

1. "Vaporization of Linear Alkanes", by L. A. Wall, J. H.

Flynn, and S. Straus, presented to Div. of Phys. Chem.

,

156th National ACS Meeting, Atlantic City, N.J.,

September 1968.

2. "Vaporization of Organic Plasticizers" , by L. A. Wall,

J. H. Flynn, and S. Straus, presented to Div. of

Polymer Chem., 156th National ACS Meeting, Atlantic

City, N.J., Polymer Preprints 9, [2], 1440 (September

1968).

3.9- Relaxations Near the Melting Point

J. P. Colson and R. K. Eby

Polymers Division

Institute for Materials Research

In the dynamic mechanical properties of mats of solutiongrown crystals of polyethylene measured with a torsion pendulum, the strength of the a relaxation depends upon the temperature of annealing. Furthermore, the relaxation correlates

with reciprocal thickness of the crystals suggesting that the

origin of the relaxation is in the crystal surface. An important question is, "Do other structural and morphological

features also change with annealing?" We have reported

previously that: (1) The orientation of the crystallographic

axes with respect to the edges of the crystal mat does not

change, (2) the unit cell dimensions do change and the area

of the basal (a,b) plane of the cell correlates with the

strength of the a relaxation. However, we have now found

25
that another parameter of importance is solvent. Samples

annealed for 4 weeks in a vacuum at 8o°C, exhibit a relaxation temperature 15°C higher than that for samples annealed

for 1 week in a vacuum at 23°C and then annealed for 30

minutes at atmospheric pressure at 80°C. These have identical lamella thickness, unit cell dimensions, and orientation of the crystal axes with respect to the edges of the

crystal mat. We have found that this difference in temperature of the a relaxation correlates with residual solvent.

The one evacuated at 23°C and annealed at 80°C contains

approximately two times as much solvent as the one evacuated

at 80°C. As the "23°C sample" is annealed at higher temperatures, its relaxation temperature rises to that of the

"80°C sample". Possibly, this correlates with the decreasing solvent content upon annealing. We plan measurements

to examine this.

26
NBS TECHNICAL PUBLICATIONS

PERIODICALS

JOURNAL OF RESEARCH reports National

Bureau of Standards research and development in physics, mathematics, chemistry, and engineering.

Comprehensive scientific papers give complete details of the work, including laboratory data, experimental

procedures, and theoretical and mathematical analyses. Illustrated with photographs, drawings, and

charts.

Published in three sections, available separately: • Physics and Chemistry

Papers of interest primarily to scientists working in these fields. This section covers a broad range of physical and chemical research, with major emphasis on standards of physical measurement, fundamental

constants, and properties of matter. Issued six times

a year. Annual subscription: Domestic, $9.50; for- eign, $11.75*. • Mathematical Sciences

Studies and compilations designed mainly for the mathematician and theoretical physicist. Topics in mathematical statistics, theory of experiment design,

numerical analysis, theoretical physics and chemistry, logical design and programming of computers

and computer systems. Short numerical tables. Issued quarterly. Annual subscription: Domestic,

$5.00: foreign, $6.25*. • Engineering and Instrumentation

Reporting results of interest chiefly to the engineer

and the applied scientist. This section includes many

of the new developments in instrumentation resulting

from the Bureau's work in physical measurement,

data processing, and development of test methods.

It will also cover some of the work in acoustics,

applied mechanics, building research, and cryogenic

engineering. Issued quarterly. Annual subscription:

Domestic, $5.00; foreign, $6.25*.

TECHNICAL NEWS BULLETIN

The best single source of information concerning the Bureau's research, developmental, cooperative and

publication activities, this monthly publication is designed for the industry-oriented individual whose

daily work involves intimate contact with science and

technology

for engineers, chemists, physicists, re- search managers, product-development managers, and

company executives. Annual subscription: Domestic,

$3.00; foreign, $4.00*.

* Difference in price is due to extra co9t of foreign mailing.

N0NPERI0DICALS

Applied Mathematics Series. Mathematical tables, manuals, and studies. Building Science Series. Research results, test methods, and performance criteria of building materials, components, systems, and structures. Handbooks. Recommended codes of engineering

and industrial practice (including safety codes) de- veloped in cooperation with interested industries,

professional organizations, and regulatory bodies. Special Publications. Proceedings of NBS conferences, bibliographies, annual reports, wall charts,

pamphlets, etc. Monographs. Major contributions to the technical

literature on various subjects related to the Bureau's

scientific and technical activities. National Standard Reference Data Series.

NSRDS provides quantitive data on the physical

and chemical properties of materials, compiled from

the world's literature and critically evaluated. Product Standards. Provide requirements for sizes, types, quality and methods for testing various industrial products. These standards are developed cooperatively with interested Government and industry groups

and provide the basis for common understanding of product characteristics for both buyers and sellers. Their use is voluntary.

Technical Notes. This series consists of communications and reports (covering both other agency and

NBS-sponsored work) of limited or transitory interest. Federal Information Processing Standards Publications. This series is the official publication within

the Federal Government for information on standards

adopted and promulgated under the Public Law

89-306, and Bureau of the Budget Circular A-86

entitled, Standardization of Data Elements and Codes

in Data Systems.

CLEARINGHOUSE

The Clearinghouse for Federal Scientific and

Technical Information, operated by NBS, supplies

unclassified information related to Government-generated science and technology in defense, space, atomic energy, and other national programs. For

further information on Clearinghouse services, write: Clearinghouse

U.S. Department of Commerce

Springfield, Virginia 22151

Order NBS publications from: Superintendent of Documents

Government Printing Office

Washington, D.C. 20402
U.S. DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20230

OFFICIAL BUSINESS POSTAGE AND FEES PAID

U.S. DEPARTMENT OF COMMERCE