Flow-tube oxidation experiments on the carbon preform of PICA

Oxidation experiments on the carbon preform of a phenolic-impregnated carbon ablator were performed in the NASA Ames flow-tube reactor facility, at temperatures between 700 and 1300 K, under dry air gas at pressures between 10³ and 10⁴ Pa. Mass loss, volumetric recession and density changes were measured at different test conditions. An analysis of the diffusion/reaction competition within the porous material, based on the Thiele number, allowed us to identify low temperature and low pressure conditions to be dominated by in-depth volume oxidation. Experiments above 1000 K were found at transition conditions, where diffusion and reaction occur at similar scales. The microscopic oxidation behavior of the fibers was characterized by scanning electron microscopy and energy dispersive x- ray analysis. The material was found to oxidize at specific sites forming a pitting pattern distributed over the fibers' surface. Calcium- and oxygen-rich residues from the oxidation reactions were observed at several locations.