Modeling air-silica surface catalysis in hypersonic environments using ReaxFF molecular dynamics

Abstract

The goal of this work is to model surface catalysis in partially dissociated Air-SiO2 systems, which is of interest for accurately predicting heating on hypersonic vehicles. This is accomplished through molecular dynamics simulations using the ReaxFF potential, which is able to accurately model chemical reactions. The performance of the ReaxFF potential for predicting the bulk structures of several different types of SiO2 is evaluated, and we find that it most accurately reproduces the structure of fi-quartz. Potential energy surfaces for several reactions of interest in catalysis show that the potential may need further training to reproduce results from Quantum Chemical Calculations. Based on a literature review of experimental results and the capabilities of the potential, we choose to model oxygen catalysis on Fi-Quartz. A methodology for measuring recombination coefficients on a silica surface is developed, and tested for gases at 10atm and 100 atm over the temperature range(600-2000K).We find that recombination coefficients are much higher than those measured experimentally, however, the trend in recombination coefficients is exponential with temperature as seen in experiment.