Oxidation of metals with highly reactive vapors: Extension of Wagner theory

In this article, a theoretical analysis of the behavior of metallic materia ls at high temperature in the presence of gaseous oxygen is presented. A ge neralized Wagner approach is presented in the limiting scenario of highly r eactive vapors, Wagner's theory being the lower limit for null reactivity. Oxygen transfer from the gas phase to the condensed phase is expressed in t erms of oxygen effective pressure, accounting for the contribution of volat ile oxides. The theoretical approach allows the prediction of the oxygen pa rtial pressures in the feed gas corresponding to oxidation/deoxidation cond itions. Such conditions can be different from those given by thermodynamic equilibrium by several orders of magnitude. Moreover, the actual oxygen par tial pressure at the condensed phase interface can be expressed as a functi on of the feed-gas oxygen content, which is measurable. The theory is appli cable for metals and nonmetallic materials, such as semiconductors, both in solid and liquid phase. An application to the molten silicon-oxygen system is presented.