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.