Kinetics, morphology and thermodynamics of the solid--liquid transition of non-metals. Progress report, March 1, 1978--February 28, 1979

Abstract

Apparatus is being assembled for measurement of the solid--liquid surface tension, ..gamma.., of two non-metallic materials, GeO/sub 2/ and NaCl, via the grain-boundary groove technique. According to this technique, a solid adjacent to its liquid is used in a temperature gradient and the shape of the solid--liquid interface near a grain boundary groove is measured. From this shape and a knowledge of the thermal field, ..gamma.., a parameter extremely important in nucleation and solidification kinetics, is calculated. GeO/sub 2/ is chosen for its low entropy of fusion and NaCl for its simple ionic bonding; both are transparent. The apparatus for GeO/sub 2/ involves a lineal geometry, a two-zone furnace and an optical viewport; that for NaCl involves an axial geometry. The thermal field for the lineal geometry was calculated by the solution of finite difference equations. If future results support the tendency for the crucible to impose its simple linear temperature gradient on thin samples, the theoretical analysis will be drastically simplified and the technique might be extendable to a broad class of materials. Previous work on the modeling of Internal Centrifugal Zone Growth has been communicated to personnel at Oak Ridge who have incorporated it in their ongoing researchmore » programs.« less