New high temperature amorphous protective coatings for Mg2Si thermoelectric material

Abstract

Magnesium silicide is one of the most promising, inexpensive, environment friendly and low density (1.99 g cm−3) thermoelectric material. These attributes distinguish it from other well-known thermoelectric materials and therefore it is currently intensively studied. Since thermoelectric materials are used in elevated temperatures, they are prone to oxygen corrosion which results in deterioration of their properties and therefore require anticorrosion protection. The aim of the work was to develop anticorrosive coating for magnesium silicide using silane-based, amorphous coatings. High purity Mg2Si samples were prepared by self-propagating high-temperature synthesis (SHS) and hot-pressing method supported by induction heater. The structural and phase compositions of the obtained samples were examined by means of X-ray diffraction (XRD) method and chemical composition analysis by scanning electron microscopy SEM, combined with EDS method. Fourier-transform infrared spectroscopy FT-IR, Raman spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), temperature-programmed reduction (TPR) and temperature-programmed oxidation (TPOx) methods were used in order to determine chemical stability of prepared samples. In final step, magnesium silicide samples were covered with selected amorphous coatings by dip-coating method and then annealed in Ar gas atmospheres in various temperatures between 400–550 °C. The obtained coatings were characterized using SEM-EDS and reflectance spectroscopy method.