Effect of Titanium Surface Roughness on Oxygen Catalytic Recombination in a Shock Tube

Abstract

Surface roughness and microscopic morphology are key factors influencing oxygen catalytic recombination. Titanium is extensively used as a material for metallic thermal protection systems (TPS) in the design of hypersonic and reusable launch vehicles. In this study, the effect of titanium surface roughness on oxygen catalytic recombination is experimentally investigated. The efficiency of the oxygen recombination reaction is determined by evaluating the measured heat-transfer rates while considering the existing theory of binary gas mixtures. The surface of the test models was coated with either titanium or silicon dioxide, and for each model, four different levels of surface roughness were prepared. It is shown that, with an increase in surface roughness, oxygen recombination efficiency increased on both the titanium and silicon dioxide surfaces. Surface topography was characterized in terms of the roughness factor (Ф = A/Ag), i.e., the ratio of the actual surface area (A) to the projected surface area (Ag) using an atomic force microscope. The relationship between the roughness factor and oxygen recombination efficiency was examined.