SiB_(4)高温热氧化机理及动力学

Thermal Oxidation Mechanism and Kinetics of SiB_(4) at Elevated Temperature

本工作以高超声速飞行器表面高发射率涂层关键填料Si B_(4)为研究对象,采用非等温热重分析法在空气条件下对粒径40μmSiB_(4)粉体高温热氧化过程以及氧化动力学进行研究。结果表明,SiB_(4)热氧化起始温度为650℃,热氧化过程质量呈现恒重→增重→恒重变化趋势,其中高温区试样恒重分别是由玻璃相包覆保护作用、氧化增重与气相挥发损失竞争作用2种机制控制。升温速率对Si B_(4)热氧化过程影响显著,升温速率越快,放热效应越明显。SiB的平均活化能为239.14 kJ/mol,动力学指前因子A=9.8696×10^(9)s^(-1),热氧化动力学函数为G(α)=ln[–ln(1–α)]^(1.7574)。

In this work, the high-temperature thermal oxidation process and kinetics of SiBpowder(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 SiBstarts 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 SiBoxidation process, and the faster temperature rises, the more obvious exothermic effect is.The average active energy of SiBpowder is 239.14 k J/mol. The kinetic preexponential factor is 9.8696×10^(9) s^(-1). The conversion function of oxidation reaction of SiBis G(α)=ln[–ln(1–α)]^(1.7574).