High Temperature Vaporization into Different Environments
Materials in extreme environments are often negatively affected by the process of vaporization. The maximum vaporization rate is determined by calculating a flux from the equilibrium vapor pressure(s) of each component. However, this maximum vaporization flux is decreased by the vaporization coefficient and the atmosphere above the material. This paper discusses each of these factors for common oxides, using SiO2 as an example. Vaporization into a vacuum is an ideal starting point, as the basic mechanisms for vaporization have been derived from these studies. Imposing an over-pressure of a static gas changes the vaporization rates from both a thermodynamic and kinetic aspect. Finally, a flowing gas is the most common situation encountered in many extreme environments. Laminar and turbulent flow effects are be treated with both analytical transport expressions and computational fluid dynamics (CFD). The example of a vaporizing SiO2 coupon in a laboratory furnace is examined with both the analytical expressions and with CFD.