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.

Melting point depression of tin nanoparticles embedded in a stable alpha-alumina matrix fabricated by ball milling

“…The Sn particle sizes of the as-milled samples were calculated to be 44, 41, 39 and 37 nm for the powders milled after 1, 2, 3 and 4hr, respectively. These results are the characteristic feature of BM and consistent with the findings in the literature [1][2][3][4].…”

“…It is suggested that abundant stored energy forms during ball milling due to the introduction of many dislocations. For instance, Koch et al [1] corroborated that ball milling of Sn and Ga particles can produce significant amounts of stored energy and further influence the melting behavior of Sn. Previous work using a lower weight ratio (1/3) of SnO 2 /Al powders also showed analogous effect [12], where both exothermic and endothermic reactions occurred.…”

“…Ball milling (BM) is known as an efficient method to reduce crystal size down to nano-meter scale [1][2][3][4]. The significant thermal energy provided by BM has been confirmed to initiate thermite reactions in various exothermic powder mixtures, which are also self-sustaining reactions [5][6][7].…”

“…Additionally, the activation energy of the aluminothermic reaction was calculated to be substantially reduced with milling time, which was attributed to the increase of Al-ZnO interfacial areas and progressing formation of nucleation sites during aluminothermic reactions [7]. Not surprisingly, BM has been widely applied in various materials to obtain nanocrystallites [2][3][4] and nanocomposites [1,[7][8]. However, there are some requirements for the reaction to be self-sustaining.…”

Thermodynamics of Nanostructured Materials

“…Melting point depressions in immiscible nanophase systems have also been found in the case where the melting phase is the matrix in which inert particles are embedded. An example is found in ballmilled Sn/Ge mixtures [28,29] ip; which the Ge particles are about 10 nm in diameter, dispersed in the Sn; the melting point of the Sn is depressed by as much as 40 K. The depression cannot be explained using eq. (13) as the interface curvature is not readily defined.…”