Model for Evaluating Silica Coating Thickness Against Atomic-Oxygen Corrosion in Space Materials

摘要

By capturing electrons from both the interaction between hyperthermal atomic-oxygen and a solid surface and the quantum tunneling effects, a fraction of atomic-oxygen would turn into atomic-oxygen anions. By virtue of qualitative analyses on the effects of oxidant species (atomic-oxygen and its anion) toward the reaction-diffusion processes, it is found that a monotonically decaying function for either the reactive rate constant or the diffusion coefficient would provide a more realistic description of the reaction-diffusion mechanisms than the existing models. Nondimensional reaction-diffusion equations with a single adjustable parameter are then deduced. Good agreement between theoretical curves and experimental data validates the modified model developed in the present work. The estimations of the diffusivity, reactive rate constant, and adjustable parameter, together with the characteristic attenuation length are presented. The dependencies of those coefficients upon translational kinetic energy, flux, temperature, as well as the tangential flux of atomic-oxygen are explained. In addition, a procedure for evaluating time evolution of oxide-layer thickness by extending the curve fitting is proposed and demonstrated. The procedure would be a useful tool for predicting protective film thickness against the atomic-oxygen reacting with spacecraft surface materials in low Earth orbit.