Thermoelectric properties of magnesium silicide deposited by use of an atmospheric plasma thermal spray

The thermoelectric properties of magnesium silicide (Mg₂Si) samples prepared by use of an atmospheric plasma spray (APS) were compared with those of samples prepared from the same feedstock powder by use of the conventional hot-pressing method. The characterization performed included measurement of thermal conductivity, electrical conductivity, Seebeck coefficient, and figure of merit, ZT. X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDX) were used to assess how phase and microstructure affected the thermoelectric properties of the samples. Hall effect measurements furnished carrier concentration, and measurement of Hall mobility provided further insight into electrical conductivity and Seebeck coefficient. Low temperature and high velocity APS using an internal-powder distribution system achieved a phase of composition similar to that of the feedstock powder. Thermal spraying was demonstrated in this work to be an effective means of reducing the thermal conductivity of Mg₂Si; this may be because of pores and cracks in the sprayed sample. Vacuum-annealed APS samples were found to have very high Seebeck coefficients. To further improve the figure of merit, carrier concentration must be adjusted and carrier mobility must be enhanced.