The Active Oxidation of Si and SiC in the Viscous Gas‐Flow Regime
The Active Oxidation of Si and SiC in the Viscous Gas‐Flow Regime
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DOI：
10.1149/1.2132997
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发表时间：
1976-07
影响因子：
3.9
通讯作者：
J. W. Hinze;H. C. Graham
中科院分区：
文献类型：
--
作者：
J. W. Hinze;H. C. Graham
研究了硅和碳化硅在粘性气流条件下的活性氧化。动力学测量作为温度和氧分压的函数使用热重技术。通过将无氧化物样品暴露在O2/Ar气体混合物中的低氧分压中，可以引发活性氧化。发现氧化速率受氧通过气体边界层的输运控制。发现硅的活性氧化发生在两个不同的阶段，而不是像预期的那样只发生一个阶段。在第一阶段观察到线性样品重量损失；然而，在第二阶段，观察到异常和破坏性的行为，以极快的样品重量增加的形式。这一现象被解释为SiO汽化和SiO2冷凝同时发生的过程。在SiC活性氧化过程中没有观察到这种行为。硅基材料，如Si3N4， SiC及其复合材料，由于其特殊的高温性能，特别是强度，抗氧化性和抗热震性，已被提出用于许多应用。许多研究者已经研究了这些材料在衬底上形成保护性二氧化硅鳞片的环境中的氧化。虽然氧化机理的细节仍不清楚（1-8），但各种研究人员发现的氧化活化能和极低的氧化速率是合理的一致。硅基材料的一个重要限制是它们在高温下氧压降低的氧化过程中倾向于形成气态产物。衬底表面要么保持裸露，要么（我们将在后面看到）生长出须状的非保护性SiO2，而不是形成保护性SiO2。在这种条件下，物质损失速度极快。通过将材料暴露于低总压下的纯氧（分子气体流动状态）或在大气压或接近大气压下的稀氧/惰性气体混合物（粘性气体流动状态），可以在高温下启动活性氧化。一些涉及Si和SiC在分子气体流动状态下活性氧化的研究结果已经被报道（9-14），并且活性氧化的机制已经被很好地理解。固体SiO2在使用的氧气压力和温度环境下是稳定的；然而，将环境氧压（Po2: PT）降低到Si-SiO2或SiC-SiO2的平衡SiO压力以下，就会引发活性氧化
The active oxidation of Si and SiC was investigated in the viscous gasflow regime. Kinetics were measured as a function of temperature and oxygen partial pressure using thermogravimetric techniques. Active oxidation was initiated by exposing oxide-free samples to low oxygen partial pressures in O2/Ar gas mixtures. Oxidation rates were found to be controlled by oxygen transport through the gaseous boundary layer. Active oxidation of Si was found to occur in two distinct stages rather than in only one as expected. Linear sample weight losses were observed during the first stage; however, in the second stage unusual and destructive behavior was observed in the form of extremely rapid sample weight gains. This phenomenon was interpreted in terms of a simultaneous SiO vaporization and SiO2 condensation process. No such behavior was observed during SiC active oxidation.Si-base materials such as Si3N4, SiC, and their composites have been proposed for a number of applications because of their exceptional high temperature properties, in particular, strength, oxidation resistance, and thermal-shock resistance. A number of investigators have studied the oxidation of these materials in environments where protective silica scales are formed on the substrate. Although the details of the oxidation mechanisms are still not well understood (1-8), the activation energies for oxidation and the extremely low oxidation rates found by various investigators are in reasonable agreement. An important limitation of Si-base materials is their tendency to form gaseous products during oxidation in reduced oxygen pressures at high temperatures. Instead of a protective SiO2 scale being formed, the substrate surface either remains bare or, as we shall see later, nonprotective SiO2 in the form of whiskers is grown. Under these conditions extremely rapid rates of material loss occur. Active oxidation can be initiated at high temperatures by exposing the material to either pure oxygen at low total pressure (molecular gas-flow regime) or dilute oxygen/inert gas mixtures at or near atmospheric pressure (viscous gas-flow regime). Results from several investigations involving the active oxidation of Si and SiC in the molecular gas-flow regime have been reported (9-14), and the mechanisms of active oxidation are well understood. Solid SiO2 was stable in the oxygen pressure and temperature environments used; however, active oxidation was initiated by decreasing the ambient oxygen pressure (Po2: PT) below the equilibrium SiO pressure at the Si-SiO2 or SiC-SiO2