Obtaining and characterisation of thermoelectric Mg2Si compound via wet and dry mechanical alloying and spark plasma sintering

Abstract

Mg2Si thermoelectric compound was obtained by dry and wet (isohexane and benzene) mechanical alloying route. The Mg2Si compound was characterised by X-ray diffraction, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), laser particle size analysis and thermoelectric measurements. After 14 h of milling, the complete reaction of the elements is achieved by both routes. The powders particle size distribution obtained after 14 h of dry or wet milling (using benzene) reveals a bimodal curve. The wet milling moves the particle size distribution towards smaller particle sizes. The SEM analysis confirms the results of particles size analysis. DSC analyses performed for samples milled up to 14 h present stress relief and recrystallisation thermal events. For the benzene wet-milled sample, the DSC curve shows an additional thermal event at 350 °C, associated with benzene removal. Thermoelectric properties were determined on spark plasma sintered compacts. The milling process with benzene leads to a higher value of Seebeck coefficient (≈580 μV/K). The electrical conductivity is low at room temperature and increases exponentially with temperature.