Silastic Thermal Protection Materials Research Progress

The silicone rubber is the main chain is a chain of a Si 101, the silicon atoms can be connected on the organic side groups of methyl, vinyl, phenyl, the molecular chain of both inorganic and organic nature of the polymer elastic material. Silicone rubber has excellent thermal stability, good resistance to high temperature, low glass transition temperature, a strong anti-nitroglycerine migration ability, good anti-aging performance, low smoke, low residue, low signature The signal characteristics of coating material is a promising less smoke ¨. 2j. Missile weapon propulsion system development, construction, light weight, thrust to weight ratio large ramjet vigorously the development and application. Ramjet missile flying at high speed when punching the role to compress the inlet air and fuel combustion, and therefore the formation of the high oxygen-rich environment in the additional chamber. The combustion chamber thermal protection materials in this oxygen-rich environment requires a high antioxidant capacity, as the current most widely used performance EPDM rubber molecular chain is basically a C-c key constitutes a very serious ablation under high temperatures and oxygen-rich environment, it is difficult to form a solid and dense carbon layer. Silastic and the main chain by a Si 101 chain be able to satisfy this requirement. "But need to be modified due to the non-polar structure of the silicone rubber itself, so that the poor mechanical properties and adhesive properties, many scholars done a lot of research and work.

A Silastic Thermal Protection Materials

    Mainly used as thermal protection materials based glue dimethyl silicone rubber, methyl vinyl silicone rubber, methyl phenyl vinyl silicone rubber
Gel. Methyl vinyl silicone rubber used. Zhang Yan and its development of the human M o 1,28,34 three different molecular structure of RTV silicone rubber in the state without any filler, based glue ablation rate of the test and found two "main glue ablation rate was significantly lower than the other two high ethylene content of the silicone rubber used for thermal protection materials. the mole fraction of each component: vinyl silicone rubber 40% to 45%, catalyst 0.25% to 0 .75% (chloroplatinic acid of H2PtCl6 · 6H: O), curing the crosslinking agent (methyl hydrogen dimethylsiloxane copolymer) from 5% to 9%, fillers (such as SiO: SiC and carbon fiber) 50% silicone rubber, vinyl content, to ensure that the rubber curing more freedom vinyl cross-linking, thereby increasing the curing density, thermal protection materials into carbon rate and heat resistance. Table 1 lists the part of the Silastic thermal protection materials formula, composition, characteristics and applications.
2 to improve the way of the thermal protection material properties of silicone rubber

2.1 particles / powder filler reinforcement
    The particulate material used for the Silastic thermal protection material reinforcement of silica, calcium carbonate, silicate, and metal oxides. The Silastic a non-crystalline structure, the gravitational force between molecules is very low, so the vulcanized products without reinforcement strength is very low (such as tensile strength is only about 8 0.3 MPa), no practical value, must therefore be With the filler reinforcement. One of the most commonly used, the most effective reinforcing filler is silica. ZHAO Feng-Qi-silica on silicon rubber insulation coating mechanical properties, adhesion properties and ablative properties. Reinforced RTV silicone rubber with silazane processing silica, when the dosage of 20, the silicone rubber tensile strength of 3.58 MPa, and continue to increase the amount of silica, but reduced the tensile strength of the silicone rubber, which may silica the amount of excess scattered uneven related. Consider the process requirements, the amount of white carbon black for 15 or less. Add 6 silica and makes silicone rubber and of HMX-CMDB propellant shear strength increased by 1.01MPa to 1.98 MPa, an increase of 96%, destroying the form of cohesive failure within the silicone rubber layer. Added silica, Silastic oxyacetylene ablation rate increases, so that the ablation resistance poor. Compared to the general fumed silica nano - SiO, reinforced silicone rubber is more effective, its mechanism of nano-SiO: particle chain and silicone rubber molecular chain of the chain structure of the complex three-dimensional network, to improve the reinforcing effect. Known by the mechanism of aging of silicone rubber, silicon-oxygen bond oxidation is mainly caused by free radical chain reactions by the oxidation of side groups, and destroy this chain reaction, the oxidation process will be blocked. Fe: O, is more commonly used antioxidants can play this role, the amount normally 3 to 5. J M J, improve the heat resistance of silicone rubber.

2.2 fiber filler reinforcement
    For thermal protection material reinforcement fiber fillers are glass fibers, boron fibers, carbon fibers, aramid fibers. Thermal Protection Materials must meet the engine high temperature, high pressure, high-speed air scour environmental requirements, fiber filler can not only reinforcing the rubber matrix also can effectively improve the performance of material ablation resistance and resistance to erosion. Carbon and aramid fibers are the most studied. ZHAO Feng-Qi ¨ correction such as glass fiber, high silica fiber, carbon fiber, aramid pulp four chopped fiber filled silicone rubber, the amount of 5 phr reinforcement effect: carbon fiber, high silica fiber glass fiber > aramid pulp. The best reinforcement effect of carbon fiber, the tensile strength of 4.52 MPa, elongation rate was 43.2%. This is due to the carbon fiber with high strength and modulus than other fibers, resulting in high the Silastic tensile strength. Fiber length and the amount is also an important factor affecting its reinforcing properties of silicone rubber: the length required to meet the best aspect ratio; the dosage required to meet the performance requirements at the same time taking into account the process performance.
    Of yamadas-l scratch and others in the study of carbon fiber reinforced silicone rubber used as a the ramjet heat protective material found only when the carbon fiber length is less than a critical value when the reinforcement, and add a small amount of silica or carbon black can significantly improve the material's Young's modulus, tensile strength and elongation of some adverse effects.