SiB₄ 高温热氧化机理及动力学

In this work, the high-temperature thermal oxidation process and kinetics of SiB₄ powder (particle size~40 μm), which is usually applied as key filler for high-emissivity coating on the surface of hypersonic vehicle, were investigated by non-isothermal thermogravimetric analysis under air condition. The results show that the thermal oxidation of SiB₄ starts at 650 ℃, and their mass along the thermal oxidation process shows a trend of constant mass → mass gaining → constant mass. The second constant mass stage occurring at high-temperature region is controlled by two mechanisms, namely, the protective effect of glass encapsulation and the competitive effect of oxidation mass gaining and volatilization of gas species. The heating rate has a significant effect on SiB₄ oxidation process, and the faster temperature rises, the more obvious exothermic effect is. The average active energy of SiB₄ powder is 239.14 kJ/mol. The kinetic preexponential factor is 9.8696×10⁹ s^-1. The conversion function of oxidation reaction of SiB₄ is G(α)=ln[–ln(1–α)]^1.7574,.