A new surface catalytic model for silica-based thermal protection material for hypersonic vehicles

Abstract

Silica-based materials are widely employed in the thermal protection system for hypersonic vehicles, and the investigation of their catalytic characteristics is crucially important for accurate aerothermal heating prediction. By analyzing the disadvantages of Norman's high and low temperature models, this paper combines the two models and proposes an eight-reaction combined surface catalytic model to describe the catalysis between oxygen and silica surface. Given proper evaluation of the parameters according to many references, the recombination coefficient obtained shows good agreement with experimental data. The catalytic mechanisms between oxygen and silica surface are then analyzed. Results show that with the increase of the wall temperature, the dominant reaction contributing to catalytic coefficient varies from Langmuir-Hinshelwood (LH) recombination (TW < 620 K) to Eley-Rideal (ER) replacement (620 K < TW < 1350 K), and then to O2 desorption (TW > 1350 K). The surface coverage of chemisorption areas varies evidently with the dominant reactions in the high temperature (HT) range, while the surface coverage of physisorption areas varies within quite low temperature (LT) range (TW < 250 K). Recommended evaluation of partial parameters is also given.