Effect of Silicone Coating on Atomic Oxygen Reactivity with Carbon Fiber Preform and Phenolic Impregnated Carbon Ablator

We have conducted a comparative study on how the presence of the anti-dust CV-1144-0 silicone coating from NuSil Technology LLC affects the atomic oxygen oxidation and ablation of heat shields, specifically phenolic-impregnated carbon ablator (PICA) and its carbon fiber preform substrate, FiberForm. Using an atomic oxygen beam-surface scattering apparatus, we measured the scattered products from the surface of the materials at temperatures from 1000 K to 1800 K. Results showed higher nonreactive vs. reactive scattering flux on coated materials compared to their uncoated counterparts up to 1500 K, around which point the silicon-oxide layer decomposed. Upon the breakdown of the oxide layer, the reactivity of the sample reverted to that of its underlying substrate, either that of FiberForm or charred PICA. In addition, a subtle influence of underlying impurities, specifically calcium, was observed in the oxidation of both PICA and FiberForm. PICA appeared to retain the presence of these impurities after ablation at 1800 K, which was attributed to a shielding effect that the phenolic resin matrix provides to the material. The data should be useful for the development of an improved PICA ablation model.