Erosion of graphite in solid-propellant combustion gases and effects on heat-transfer

This paper presents the results of an analytical study and analysis of test data indicating that the erosion of graphite and graphite reinforced plastics in an aluminized solid-propellant rocket motor is primarily the result of a chemical reaction occurring at the surface. The extent of chemical erosion is dependent upon the nature of the reaction, rate limited or diffusion limited, and by the chemically active species occurring in the boundary layer. The effect of high-temperature chemical reactions on heat-transfer rates to the graphite surface has also been investigated and is presented in this paper. The primary constituents in the exhaust stream of an aluminized polybutadiene acrylic acid ammonium perchlorate propellant reacting with the graphite were found to be H2O, CO2, O2, O, and OH. The reaction of these species with graphite is an endothermic reaction resulting in a substantial reduction in the heattransfer rate to the surface. The chemical erosion of graphite has been expressed as simply a function of the reacting species, wall temperature, and enthalpy heat-transfer coefficient. The effects of chemical erosion of graphite on convective heating rates may be accounted for by the net heats of reaction involved or by the resulting effect on wall enthalpy.