Flow-Tube Oxidation Experiments on the Carbon Preform of a Phenolic-Impregnated Carbon Ablator

Oxidation experiments on the carbon preform of a phenolic-impregnated carbon ablator were performed in a flow-tube reactor facility, at temperatures between 700 and 1300K, under dry air gas at pressures between 1.6x103 and 6.0x104Pa. 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, allows identification of low temperature and low-pressure conditions to be dominated by in-depth volume oxidation. Experiments above 1000K 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 surface of the fibers. Calcium- and oxygen-rich residues from the oxidation reactions were observed at several locations.