The melting point depression of tin in mechanically milled tin and germanium powder mixtures

Abstract

A melting point depression, δTM, has been observed for Sn in Ge/Sn (50 at.% Sn) dispersions which were prepared by mechanical milling of Ge and Sn powders. Sn and Ge are immiscible and form a fine dispersion of the pure components when milled in a high energy ball mill. The magnitude of δTM, as measured by DSC, increases with milling time, i.e., with refinement of the dispersion. Melting is observed to begin as low as 36 °C below the equilibrium bulk melting temperature. The magnitude of δTM is reduced by about 25% after melting the Sn. Subsequent remelts do not change δTM further. Impurities cannot account for δTM. While stored energy of cold work may contribute to 25% of δTM before Sn is melted, it is concluded that the major contribution to δTM comes from the nucleation of disorder/melting at the Ge/Sn interfaces.