Thermoelectric investigation of solidification of lead II. Lead alloys

Abstract

Measurement techniques, based on the Seebeck effect method described in Part I, have been adapted to enable distribution and diffusion coefficients to be determined in dilute alloys, via the detection of temperature changes at the solid-liquid interface. Values of the distribution coefficient ( k = 0.745 ± 0.009) and liquid diffusion coefficient ( D L = 0.9 (±0.2) X 10 −9 m 2 s −1) for tin in a dilute lead based alloy were obtained. A dilute lead-silver alloy was also investigated by the same technique, and a value of D L (1.5 (±0.3) X 10 −9 m 2 s −1) obtained for the solute. The conditions for breakdown of a planar interface, and the velocity-undercooling relationship for subsequent cellular growth were also evaluated via thermoelectric measurement of the interface temperature. A separate technique was developed for non-invasive measurement of solute redistribution in zone refining, utilizing the effect of impurity concentration on the thermoelectric power of a material. This method was used to obtain an estimate for the effective distribution coefficient of an impurity during zone refining.