Synthesis and characterization of Mg-Si thermoelectric compound subjected to mechanical alloying

We have applied mechanical alloying (MA) to get Mg2Si thermoelectric material with nano-sized grains. An optimal milling and heat treatment conditions to obtain the single phase of Mg-2 Si compound with fine microstructure were investigated by X-ray diffraction and differential scanning calorimetry (DSC) measurement. The Mg66.7Si33.3 MA samples ball-milled for 20-180 hrs exhibit two broad exothermic heat releases around 220(circle)C and 570(circle)C. On the other hand, MA sample ball-milled for 260 hrs exhibits only a sharp exothermic peak at 230(circle)C Single phase Mg2Si powder can be obtained by MA of Mg66.7Si33.3 mixture for 60 hours and subsequently heated up to 620(circle)C. Sintering of the MA powders was performed in a spark plasma sintering (SPS) machine using graphite dies at 800-900(circle)C under 50 MPa. The shrinkage of sintering sample during SPS was significant at about 200(circle)C. All compact bodies have a high relative density above 94 % with metallic glare on the surface.