Vaporization of Protective Oxide Films into Different Gas Atmospheres

Abstract

Vaporization often accompanies high-temperature oxidation and corrosion. In this review, vaporization under a vacuum as well as static gas and flowing gas conditions is discussed. The focus is on common protective oxides—Cr2O3, SiO2, and Al2O3. However, the methods and conclusions apply to other oxides as well. Vaporization into a vacuum is an ideal starting point, as the basic mechanisms for vaporization have been derived from these studies. Imposing an overpressure of a static gas changes the vaporization rates from both a thermodynamic and a kinetic aspect. Finally, a flowing gas is the most common situation encountered in high-temperature oxidation and corrosion. Laminar and turbulent flow effects are treated with both analytic expressions for mass transfer and computational fluid dynamics (CFD). A vaporizing SiO2 coupon in a laboratory furnace is examined with both the analytic expressions and the CFD approach.