Mechanically induced reaction for solid-state synthesis of Mg₂Si and Mg₂Sn

Magnesium base compounds have unique properties as a functional material. The conventional melting and solidification and mechanical attriting/grinding methods have to suffer from various difficulties in synthesis of these compounds: large difference in melting temperature among elemental constituents and various contaminations in material processing. Bulk mechanical alloying (BMA) is attractive for solid-state synthesis of these types of magnesium compounds, especially Mg₂X for X=Si and Sn. High dense, single phase Mg₂X compact is successfully fabricated by this processing. Electrical conductivity of Mg₂X is measured to describe its semi-conductivity. This solid-state reaction at room temperature is mechanically induced during BMA so that the solid-state reactivity is dependent on the physical properties of each element X. In the case of ductile-brittle phase system like Mg-Si, its solid reaction process is directly controlled by mechanical refinement of silicon particle size in the magnesium matrix. In the case of ductile-ductile phase system like Mg-Sn, its solid-state reactivity is enhanced by the repeated plastic flow of ductile constituents. The above mechanically induced solid-state reaction process is described with consideration of formation enthalpy ratio in Mg-X system varying during BMA. Transient behavior of thermoelectricity from metallic state to semi-conductive one is also described by the simple mixture rule of this formation enthalpy ratio.