Decomposition and permeability of room temperature vulcanizing (RTV) silicone

Room temperature vulcanizing (RTV) silicone is used to join thermal protection system (TPS) tiles and attach the entire TPS system to the surface of space capsules. The RTV allows expansion and contraction from temperature changes during atmospheric entry, which avoids cracks in the brittle TPS tiles. Two types of RTV are heated to various temperatures at different heating rates in a high-temperature furnace and a thermogravimetric analyzer to understand the decomposition of RTV during entry of spacecrafts. X-ray computed tomography (XRCT) is used to create three-dimensional virtual volumes of the RTV material decomposed in a furnace. The volumes obtained from XRCT, and the mass loss curves from the thermogravimetric analyzer and the high-temperature furnace are used to understand the structure of RTV as it decomposes. It is found that RTV materials burn from the inside, creating cavities inside the material while pushing the exterior material outwards, and causing inelastic deformation of the RTV material. The two RTV samples decompose in different patterns depending on the heating rate, but the internal decomposition process is similar with both materials forming cavities, eventually resulting in a permeable material that allows gases to flow through them. It is found that the RTV is impermeable from temperatures between 200 to approximately 350 ◦C, where mass decomposition is not significant, and there is minimal decomposition of the material. However, after 350 ◦C, the mass loss and material decomposition significantly increases, making the RTV permeable. The three-dimensional volume of RTV obtained after heating to 600 ◦C is used as an input to compute the effective permeability of the decomposed RTV material.