Perspectives on nucleation
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Perspectives on Nucleation
G. M. POUND R.F. Mehl Medalist
The present status of several active areas in the field of nucleation is briefly reviewed. It is concluded that: (1) the agreement of classical nucleation rate theory with critical supersaturation measurements in the homogeneous nucleation of droplets from the supersaturated vapor is probably fortuitous; (2) in terms of classical nucleation theory, the shape of the nuclei in solid/solid nucleation, and hence resulting orientation relationships, are largely determined by capillarity considerations; (3) Cahn and associates are building a new thermodynamics of solids which will likely prove to be of great value in nucleation theory; (4) the strongest experimental support for nucleation theories would appear to be the measurements by Servi and Turnbull and by Le Goues and Aaronson on the coherent homogeneous nucleation of cobalt from dilute copper-cobalt solid solutions; and (5) in future work, computer statistical mechanics may offer an alternative approach to nucleation rate theory which circumvents the questionable assumptions of present treatments.
The Institute of Metals Lecture was established in 1921, at which time the Institute of' Metals Division was the only pror Division within the American Institute of Mining and Metallurgical Engineers. It has been given annually since 1922 by distinguished men .from this country and abroad. Beginning in 1973 and thereafter, the person selected to deliver the lecture will be known as the "Institute of Metals Division Lecturer and R.F. Mehl Medalist" r that year. Dr. GUY MARSHALL POUND recently retired as Professor of Materials Science and Engineering, Stanford University. He received his B.S. in chemistry from Reed College in 1941, his M.S. in chemical engineering from M.I.T. in 1944, and his Ph.D. in physical chemistry from Columbia University in 1949. From 1944-46, Dr. Pound was a chemical engineer at California Research Corporation. His teaching career at Carnegie Institute of Technology began in 1949, and he was director of the Metals Research Laboratory there from 1960-66. In 1966 he joined the faculty at Stanford University, where from 1977-79, he also served as director of the Stanford/Ames-NASA Joint Institute for Surface and Microstructural Research. In addition, Dr. Pound has conducted contract research on the kinetics of phase transformation for various agencies of the government for more than 25 years. A 1983 Fellow of The Metallurgical Society of AIME, Dr. Pound is the author of numerous publications and the recipient of many honors and awards, including the Albert Easton White Distinguished Teaching Award of ASM-1978. METALLURGICAL TRANSACTIONS A
I.
INTRODUCTION
THE purpose of this
work is to summarize briefly certain important and active areas in the field of nucleation with the view to establishing the best basis for our present nucleation theories. Although almost all nucleation is heterogeneous, the following discussions will deal mostly with homogeneous nucleation. This is because the prese
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