Thermal Properties of Gold-Silicon Binary Alloy Near the Eutectic Composition

摘要

We have measured the specific heat, CP, and the enthalpy of Au-18.6 at % Si alloy in some of its various forms. CP of the liquid form falls continuously with increasing temperature from 8.38 plus or minus 0.05 at 563K, corresponding to an undercooling of 73K, to 7.90 plus or minus 0.05 cal/gfw-K and it exhibits no singular behavior at the melting temperature, Tm. It exceeds the heat capacity of the eutectic solid by 1.87 cal/gfwK at Tm. This high specific heat in the liquid state and its decrease with increasing temperature is attributed principally to the configurational entropy as has been suggested for the pure liquid metals. CP of the amorphous alloy, formed by rapidly chilling the liquid, was measured for the temperature range from 208 to 278K. It rises slowly to 225K, then falls, and then rises again with increasing temperature. It exceeds CP of the eutectic solid by 0.2 to 0.4 cal/gfw-K. CP of the metastable intermetallic crystalline phase, formed when the liquid is less rapidly chilled, falls between the values for the eutectic and amorphous solids. The especially deep lying eutectic exhibited by this system is attributed to the tendency for unlike atoms to associate when in the metallic state, in contrast with the strong tendency for phase separation in the solid state owing to the high stability of silicon in its covalent crystalline form. (Author)