Transition of catalytic recombination pathways on silica-based thermal protection materials at different temperatures using reactive molecular dynamics method

Silica-based ceramic material is one of the most competitive options of thermal protection material. However, catalytic reaction mechanism of gaseous atoms on it is complex and confusing. To model catalytic recombination of dissociated oxygen atoms accurately in prediction of chemical non-equilibrium flow and aerodynamic heating, reactive molecular dynamics (RMD) method was adopted to simulate gas-surface interaction (GSI) on the interface and a series of post-processing methods were constructed to analyze recombination pathways of atomic oxygen on α-quartz. It was found that there are 4 types of adsorbates on α-quartz surface and 5 pathways to produce recombined oxygen molecules. Recombination pathways would change from Eley-Rideal recombination-dominated to molecule desorption-dominated with increase of temperature. Information extracted by current post-processing methods explains how and why the recombination coefficient changes with temperature. The post-processing methods can be further applied in analysis of catalytic recombination on other thermal protection materials.