Sensitivity Analysis of the Catalysis Recombination Mechanism on Nanoscale Silica Surfaces

A deep understanding of surface catalysis recombination characteristics is significant for accurately predicting the aeroheating between hypersonic non-equilibrium flow and thermal protection materials, while a de-coupling sensitivity analysis of various influential factors is still lacking. A gas-solid interface (GSI) model with a hyperthermal flux boundary was established to investigate the surface catalysis recombination mechanisms on nanoscale silica surfaces. Using the reactive molecular dynamics (RMD) simulation method, the effects of solid surface temperature, gas incident angle, and translational energy on the silica surface catalysis recombination were qualified under hyperthermal atomic oxygen (AO), atomic nitrogen (AN), and various AN/AO gas mixtures' influence. It can be found that, though the Eley-Rideal (E-R) recombination mechanism plays a dominant role over the Langmuir-Hinshelwood (L-H) mechanism for all the sensitivity analyses, a non-linear increasing pattern of AO recombination coefficient γ_O2 with the increase in incident angle θ_in and translational energy E_k is observed. Compared with the surface catalysis under hyperthermal AO impact, the AN surface adsorption fraction shows an inverse trend with the increase in surface temperature, which suggests the potential inadequacy of the traditional proportional relationship assumptions between the surface adsorption concentration and the surface catalysis recombination coefficient for other species' impact instead of AOs. For the incoming bi-component AO/AN gas mixtures, the corresponding surface catalysis coefficient is not the simple superposition of the effects of individual gases but is affected by both the intramolecular bond energies (e.g., O₂, N₂) and intermolecular energies (e.g., Si/N, Si/O).