Contact: Dr. Madeleine Watson

Transpiration cooling has long been proposed as a thermal protection system for sharp leading edges on hypersonic vehicles. During operation, these parts are exposed to temperatures in excess of 2000 ºC, which makes high melting Ultra-High Temperature Ceramics (UHTCs) lead candidates fabricating such parts. However, UHTCs are generally Borides and Carbides, which tend to convert to much lower melting oxides under the plasma heading conditions created in hypersonic flight. Working with a team of hypersonic engineers at the University of Oxford, this project aims define parameters for generating protective layers of laminar flowing inert gasses across the surface of leading-edge parts. 

Currently, we aim to probe the relationship between gas flux, laminar flow layers and surface concentrations of oxygen species. From a materials standpoint, engineering laminar flow layers requires materials with very consistent distributions of open porosity, which in the past we have successfully achieved by partially sintering 3-5um particles of the UHTC ZrB2 to approximately 65% density. However, the easiest way to quantify local oxygen concentrations is with surface bound oxygen-responsive fluorophores, also known as oxygen partial- pressure sensitive paint (PSP), and PSP does not stick well to ZrB2. Luckily, PSP sticks well to Alumina.  Toward this aim, we have produced partially-sintered porous alumina from size matched alumina feedstocks, allowing us to visualise local surface oxygen concentration as a function material density and transpiring gas pressure.