Effect of Oxygen Partial Pressure and Temperature on the Oxidation Behavior of SiB 6

The oxidation kinetics of silicon hexaboride (SiB6) was studied at different partial pressures of oxygen. The specific weight gain was measured at 1173 K, 1223 K, and 1273 K for \( P_{{{\text{O}}_{2} }} \) = 0.1, 0.23, and 0.33 atm using thermogravimetric analysis. The conventional empirical expressions for oxidation were observed at all selected oxygen partial pressures and temperatures. The structural characterization of the oxidation product was characterized using XRD and FT-IR, with SiB6, SiO2, B, and amorphous B2O3 observed after oxidation for 25 hours. The oxidation surface morphology was also characterized to obtain the oxidation product size, ranging from 4.54 to 24.69 µm with increasing \( P_{{{\text{O}}_{2} }} \) and temperature. The diffusional activation energy for the oxidation process was also calculated from the empirical constant, obtained from the mathematical fitting of the specific weight gain with time. The oxidation activation energies for SiB6 are 250.72, 235.64, and 232.65 kJ/mol at \( P_{{{\text{O}}_{2} }} \) = 0.1, 0.23, and 0.33 atm, respectively.