High Temperature Oxidation of Intermetallic SiB6 Compound

The Si-B system mainly contains SiB3, SiB6, and SiBn (n = 14 – 50) phases shown to have high temperature performance as thermoelectric (TE) materials and thermal barrier coatings (TBC). Among these phases SiB6 is the most thermodynamically stable in an inert atmosphere but not well understood its oxidation behavior. Thermodynamic analyses were conducted to calculate the equilibrium composition of different Si-B phases formed during the oxidation process. The oxidation rates of SiB6 as function of temperature and oxygen partial pressure were determined by weight gain measurements using TGA. The reaction products were characterized using XRD, FTIR and SEM. The flower petal-like oxidation products were formed, and the petal size increases significantly with increase in temperature but not so significant size increase with increase in oxygen partial pressure. This further confirms that the SiB6 oxidation phenomena is highly temperature dependent. The typical parabolic rates for oxidation were observed. From the oxidation rate constants data, activation energies were calculated and compared with data available on other boride compounds