Containerless Undercooling and Solidification of Pure Metals.

Abstract

Drop tubes and electromagnetic levitation are described as techniques for containerless processing. The constraints of maximum undercoolability of metals are discussed with respect to thermodynamic considerations and the onset of homogeneous nucleation. Dendrite growth occurring in undercooled melts is described on the basis of experimental investigations and modern dendrite growth theories. The importance of the knowledge of thermophysical properties in the understanding of both nucleation and crystal growth in undercooled melts is pointed out. Experimental techniques are presented which allow the measurement of the dependence of such properties on temperature in particular by using electromagnetic positioning in future space missions.