Processing, Characterization, and Oxidation Resistance of Glass-Ceramic Coating on CoSb3

Power generation based on thermoelectric (TE) materials is very attractive due to its low environmental impact and waste heat recovery. Thermoelectric materials based on cobalt triantimonide CoSb3 exhibit one of the highest energy conversion efficiencies, revealing thermoelectric figures of merit, ZTs > 1, but undergo oxidation above 380 °C and sublimation above 500 °C. In this work, a glass-ceramic coating was chosen to match the coefficient of thermal expansion (CTE) of the TE substrate 9.2 × 10−6 K−1 (200–400 °C), deposition temperature (max. 700 °C), and maximum working temperature (600 °C). Coating processing involved the production of glass powder and glass-ceramic sintering. The glass-ceramic and the coating/CoSb3 interface were systematically investigated by means of dilatometry, X-ray diffraction, and scanning and transmission electron microscopy. As a result, a coating with good substrate coverage and adherence was developed. Finally, oxidation tests were carried out at 500 and 600 °C in order to assess the protective properties of the glass-ceramic. Microstructural and chemical composition analysis indicated limited protective properties of the coating.