High temperature oxidation behavior of cobalt triantimonide thermoelectric material

The oxidation behavior of CoSb3 thermoelectric material in air has been studied from 500 °C to 650 °C. The present work showed that the growth of oxide scale on CoSb3 material obeyed a parabolic law from 500 °C to 600 °C, while tremendous weight loss occurred at 650 °C owing to the sublimation of Sb2O3. The oxidation activation energy of CoSb3 was estimated to be 37.4 kJ/mol. SEM and XRD results showed that the oxide scale of CoSb3 was the mixture of Sb2O3 and CoSb2O6 when CoSb3 was oxidized below 600 °C; whereas the oxide scale consisted of an outer layer of Sb2O3 and an inner layer, which was composed of Sb2O3 and CoSb2O6, when CoSb3 was oxidized at 650 °C. Cracks appeared at the scale/CoSb3 interface after a certain oxidation time. The oxidation mechanism of CoSb3 material was discussed. After oxidation at 650 °C for 48 h, thermoelectric performance of CoSb3 declined obviously and ZT value decreased from 0.24 to 0.17 at 327 °C.