High Pressure Methods in Solid State Research

184 Pages·1969·21.405 MB·English

by  C. C. Bradley

C.C. Bradley
High Pressure
Methods in Solid
State Research
ACKNOWLEDGMENTS
I would like to express my gratitude to Mr. N. B. Owen of the
National Physical Laboratory for reading and commenting on a
large part of the manuscript and particularly for his help in
preparing Appendices A and B.
I would like to thank also my wife, Vivien, for her assistance and
encouragement.
C. C. Bradley
HIGH PRESSURE METHODS
IN
SOLID STATE RESEARCH
Springer Science+Business Media, LLC
©
Springer Science+B usiness Media New York
1969
Originally published by Butterworth & Co. (Publishers) Ltd in 1969
Softcover reprint of the hardcover 1st edition 1969
ISBN 978-1-4899-5879-2 ISBN 978-1-4899-5877-8 (eBook)
DOI 10.1007/978-1-4899-5877-8
Suggested U.D.C. number: 621-186.5
Suggested additional number: 66.083.2
Library of Congress Catalog Card Number: 68-58922
CONTENTS
PAGE
Acknowledgments v
l. Introduction ..
2. Construction Materials for High-Pressure Apparatus 15
3. Hydrostatic Pressure Apparatus 24
4. Opposed Anvil Apparatus 52
5. Multi-anvil Devices . . 87
6. Piston and Cylinder Apparatus for Pressures up to
100 Kilobars 122
7. Miscellaneous Methods 142
Appendix A. Materials Commonly Used in High-Pressure
Apparatus 168
Appendix B. Suppliers of Materials and Equipment in the
United Kingdom 171
Index 173
Vll
1
INTRODUCTION
In recent years the use of the pressure parameter in materials
research has increased enormously. It is probably true to say that
the growth rate in the 1960s compares favourably with that of
liquid helium temperature research in the 1950s. It has been
estimated that there are of the order of three hundred laboratories
actively engaged in making high pressure measurements, and
nearly six hundred papers on the subject were published in 1965.
By far the greatest growth has been in the United States and the
National Bureau of Standards has set up a data centre at Brigham
Young University, Utah, to compile all published high pressure
work. In other countries the growth rate has been at a lower level,
although in the USSR the Institute for High Pressure Research
of the Academy of Sciences, Moscow, has been to the forefront in
this field for many years. Probably the most important event has
been the synthesis of diamond at high temperature and high pressure
by General Electric Co., (U.S.A.) and by A.S.E.A. Co. (Sweden)
and its wide economic consequences. The basis of the most important
techniques in high pressure research were worked out by the late
P. W. Bridgman and the debt to him will be obvious from the
descriptions given in the remainder of this book.
Before discussing briefly the significance of the degree of pressure
it is useful to define the units which are commonly used. These
are the bar (b) and kilobar (kb), the atmosphere (atm), kilograms
per square centimetre (kg/cm2) and pounds per square inch
(lb/in2). The unit adopted in this book is the bar (or kilobar) in
common with the vast majority of high pressure researchers. The
equivalence of the units is given below.
1 Bar = 106 dynes/cm2 = 0·9869 atmospheres (normal)
== 1·0197 kg/cm2
14·5041b/in2
It can be said that almost any experiment capable of being carried
out at ordinary room conditions can be performed at 10 kb with
modern advances in sophistication of high-pressure techniques.
Fermi surface contours have been measured in single crystals up
to 8 kb at 4·2°K and nuclear magnetic resonance experiments in
INTRODUCTION
the 60 kb region are possible. This is not the upper limit by any
means, but as the pressure range is widened effects arising from
the method of transmitting pressure to a material become increas
ingly important. Above approximately 30 kb at room temperature
hydrostatic pressure media cannot be used since they freeze and
they are replaced by soft solids which have small but significant
shear moduli and hence may introduce inhomogeneous forces.
Above 80 or 90 kb the absolute pressure scale is not well established,
although individual measurements referred to an arbitrary scale
can be made quite accurately.
The present limit of static pressure experiments is about 500 kb
and the only available method for producing pressures above this
is by shock wave techniques. Since this method is beyond the scope
of the normal solid state research laboratory it has not been con
sidered in this book. There are several comprehensive reviews and
the reader is referred to them for further information1•2•
A number of books have been published during the last four or
five years containing review articles on a wide variety of phenomena
at high pressure and it would be pointless (and virtually impossible)
to attempt a summary. Some of them are listed at the end of the
chapter.
The purpose of this book is to give the interested reader an
insight into the design and limitations of high-pressure apparatus
over the whole range of static pressures to 500 kb. Bridgman's
classic book The Physics qf High Pressure (published by G. Bell and
Sons, 1958) contains several chapters on techniques dealing almost
exclusively with the hydrostatic range. Wentorf's Modern Very High
Pressure Techniques contains more modern methods concentrating
exclusively on the range above 30 kb. The design and construction
of the apparatus described in later chapters is well within the
capabilities of the technical services of most research laboratories
but in any case there are many small engineering firms anxious to
provide a service in this field.
It is not the aim of the book to provide a complete review of all
the methods which have been devised and for the most part original
versions are chosen for description since modifications of these are
to a large extent the individual efforts of a number of different
experimenters.
Many of the devices described in detail in subsequent chapters
have been built at the National Physical Laboratory and used by
the author and his colleagues. Suitable construction materials are
given in Chapter 2 and Appendix A and are basically those which
can be obtained easily in most scientifically developed countries.
2
PRESSURE TRANSMISSION AND MEASUREMENT
Emphasis has been placed on the use of well-established materials,
for example nickel steels, since although there may be available
new materials of preferred properties these may not have been
tested over a large enough period to justify unqualified recommenda
tion. Specifications, particularly for steels, have been given, and
the particular compositions are given in Appendix A.
The question of safety precautions in high-pressure experiments
should not be understated. There is considerable stored energy in
materials at high pressure particularly in gases and liquids and it
is important at all stages to incorporate adequate safety screens
around apparatus in which high pressure is being generated.
PRESSURE TRANSMISSION AND MEASUREMENT
As has been stated previously this book is concerned exclusively
with the problem of generating and measuring static pressures.
The range 0-500 kb is conveniently divided at around 30 kb into
two regions for the purpose of discussing pressure transmission and
calibration. In the low pressure range 0-30 kb the pressure media
used usually are fluids and a sample is subjected to truly hydro
static pressures with no shear effects. In the higher range solid
transmitting media are employed resulting in varying degrees of
uniformity of pressure. In this case there is always a finite shear
stress, albeit quite small in solids like silver chloride and boron
nitride, but it can effect the onset of phase transitions in some cases.
In the range 0-30 kb pressure is usually monitored continuously
with either a Bourdon tube (below 5 kb) or manganin resistance
manometers, these being calibrated against given fixed points or
free piston gauges. In the higher range the normal procedure is to
determine the applied load versus pressure relation at a few fixed
points and to extrapolate. The applied load then serves as a measure
of the pressure. In the case of piston and cylinder apparatus fairly
sensible friction corrections can be made to load over area values
but in the case of compressible gasket apparatus this is not possible
and measurements depend heavily on the extrapolations. This
latter method has to be used since continuously recording mano
meters such as the resistence gauge would be subjected to large
uncertainties arising from inhomogeneous straining. In spite of
this, they have been used by a few researchers for this pressure
region.
Many laboratories have investigated pressure measurement in
detail and it forms a major undertaking in high pressure research.
3
INTRODUCTION
However, the aim here is to give fairly convenient methods which
are reliable within the limits stated.
0-30 kb Range
The most fundamental method of measuring pressure in fluid
systems is to balance against a column of mercury. This is limited
to pressures of a few hundred bars with a few exceptions and is
inconvienent to use.
A second primary standard up to 26 kb is the dead weight or free
piston gauge. In this the fluid pressure is balanced by a piston
loaded with weights. There are several versions available and
accuracies up to 0·1 per cent can be obtained. These are really
only convenient in a laboratory which is well set up to make this
kind of measurement (Chapter 3).
The most convenient method is to use a manganin resistance
manometer (Chapter 3). This was first used extensively by P. W.
Bridgman who showed that the resistance versus pressure relation
is linear to 0·1 per cent up to 12 kb and to 2 per cent at 25 kb3•
Manganin resistance gauges are very easy to make and to use
Table 1.1
Nature of
Material Pressure, kb Reference
discontinuity
{Freezing point at 0°C 7·569 ± 0·001 18
Mercury Freezing point at +20°C 11·54 ± 0·02 19,20
Freezing point at -20oc 2·677 ± 0·002 20
Carbon tetrachloride Freezing point at 20°C 3·310 ± 0·010 20
Bismuth 1-11 Solid-Solid 25°C 25·38 ± 0·08 21
Bismuth 11-111 Solid-Solid 25°C 26·97 ± 0·20 21
Bismuth 111-V* Solid-Solid 25°C {89 ± 2 24
78 -82 25
Caesium 1-11 Solid-Solid 25°C 22·6 ± 0·6 21
Caesium 11-111 Solid-Solid 25°C 41·7 ± 1·0 21
Thallium 11-111 Solid-Solid 25°C 36·69 ± 0·2 21
Barium l-Ilt Solid-Solid 25°C 58·5 ± 0·5 7
59·2 ± 1·0 22
Tin* Solid-Solid 25°C 114 23
Iron* Solid-Solid 25°C 133 23
Barium 11-111* Solid-Solid 25oC 144 23
Lead* Solid-Solid 25°C 160 23
Rubidium* Solid-liquid(?) 25oc 193 23
Calcium* Solid-Solid 25°C 375 23
• These pomts to be treated w1th cautiOn (see text).
t Recently Haygarth et al. te have redetermined the Barium 1-11 point in a modified single stage
piston and cylinder apparatus. Their value of 55·0 ± 0·5 kb (at 25°C) is below that normally
quoted. Hence this fixed point should be regarded now as tentative until there is further evidence
from other sources.
4
PRESSURE TRANSMISSION AND MEASUREMENT
although differences up to l per cent in the resistance/pressure
slope may occur in winding different coils from the same spool. If
properly heat and pressure cycled initially they are very reproducible
with negligible hysteresis effects. Two calibration fixed points are
ooc
usually used, the freezing pressure of mercury at (7·569 kb) and
the I-II transition in bismuth at 25·4 kb (Table 1.1). Alternatively
calibrations against a free piston gauge can be made up to 26 kb.
The accuracy of the resistance gauges is obviously increased by
enlarging the number of fixed points and it has been suggested that
other points found in Table 1.1 are used4• However for most pur
poses an accuracy of about 0·3 per cent is quite adequate and is
obtained easily with two calibration points. The effects of temper
ature are neglible up to 35°C but beyond this point care should be
exercised in pressure measurements. Further details of manganin
manometers are given in Chapter 3. Other resistance gauges such
as gold-chrome have proved to be not as reproducible as manganin
and hence are not used widely.
30-90 kb Range
The method of calibration in this range, where pressure is usually
transmitted by soft solids, is by a number of 'fixed' points resulting
from polymorphic transitions in a number of common substances.
Generally a load versus pressure relation is obtained by extrapolation
between the fixed points and subsequent measurements are made
by reading off at the appropriate load value. (Recently a free piston
gauge usable to 100 kb has been built by Vereshchagin et aU but
it has not been used extensively as yet.)
The use of polymorphic transitions as calibration points arose
from the work of Bridgman5•6 on pressure/volume and pressure/
electrical resistance relations in a large number of elements and com
pounds. A number of phase changes in the range up to 100 kb
proved to be both easily measured and reproducible. These
together with sharpness are the main requirements for a fixed
point. As yet it is not possible in general to compare on an absolute
basis with free piston gauges and the best compromise is to measure
the transitions in a piston and cylinder apparatus and to make
corrections to the load over area pressure value for the friction and
bore distortion. This was the procedure adopted by Bridgman and
more recently by Kennedy and La Mori8• Unfortunately the limita
tion of piston and cylinder apparatus means that calibrations
above 60 kb are not easily made and any fixed point in this range
has to be regarded as tentative.
5