Page 319 - Academic Press Encyclopedia of Physical Science and Technology 3rd Chemical Engineering

P1: GSY/GSR/GLT P2: GLM Final Pages Qu: 00, 00, 00, 00
Encyclopedia of Physical Science and Technology EN007E-968 June 30, 2001 17:35

High-Pressure Synthesis

(Chemistry)

R. H. Wentorf, Jr.
R. C. DeVries

General Electric Corporate Research and Development

I. General Remarks about Pressure
II. Pressure as a Thermodynamic Variable
III. Methods for Generating Very High Pressures
IV. General Considerations of Phase Changes
V. Practical Uses of Very High Pressures
VI. Journey to the Center of the Earth

GLOSSARY no permanent change after they are removed. In the
plastic or failure stress range, the body is permanently
Cubo–octahedron Crystal having the faces of both the deformed.
cube and the octahedron.
Emf Electromotive force, measured in volts.
Gasket Softer or more deformable plastic material placed “VERY HIGH PRESSURES” means those generally
between harder materials, usually to seal a gap. above 10 kbar (kilobar), or 1 GPa (gigapascal). Confine-
Nucleation Process by which the first tiny groups of ment methods for almost any substance can usually be
atoms or molecules form a nucleus on which a crystal found, and working temperatures may range from about
can grow. Growth is easier than nucleation. 1 to 4000 K. The generation and use of such pressures
Prestressed Part of a structure carries some stress even entail special techniques and small volumes of material;
before the structure is under load. With prestressing, therefore, the industrial uses of such pressures are limited
certain structures can carry higher loads because the to the preparation of materials of high unit value such as
stresses under load are more uniform. diamond and cubic boron nitride. However, for scientific
Stress Force per unit area on any imaginary plane in an investigations, small working volumes do not matter so
object. Stresses perpendicular to the plane are com- much and very high pressures are widely used, particu-
pressive or tensile; stresses parallel with the plane are larly by those interested in the solid state of matter or the
shear stresses. Up to the elastic limit, stresses produce interiors of the earth and other planets.

365