Preparation and properties of RTV silicone rubber composites

The RTV silicone rubber reinforced by fumed silica, ferric oxide and short carbon fiber was prepared. The effect of fumed silica contents, surface treatment and contents of short carbon fiber on the properties of RTV silicone rubber was investigated. Considering the mechanical properties and processability, the optimal content of fumed silica was chosen. The pretreatment of short carbon fiber contributes to the properties improvement of RTV silicone rubber, especially the HNO₃-KH550 two-step treatment. The mechanical properties, heat-tolerance and anti-ablation properties of RTV silicone rubber were gradually improved with the content increase of carbon fiber treated by the HNO₃-KH550 two-step method. When 8 phr of carbon fiber was used, the tensile strength and tear strength of RTV silicone rubber reach 5.7 MPa and 23.2 kN/m, respectively. The onset decomposition temperature is about 10°C higher than that of RTV silicone rubber without carbon fiber, and the linear and mass ablation rates decrease to 0.046 g/s and 0.060 mm/s respectively. During the ablation process, the carbon fiber promotes the formation of the carbonized layer and acts as skeleton to keep the material integrality.