Failure Mechanism Study of Silicon Rubber Under High-Low Temperature Cycling

The ageing studies of silicon rubber applied for the gasket material in wet capacitors were proposed in the present study. Based on the extreme environment of high-altitude area, the silicon rubbers were impregnated in benzyl toluene (M/DBT) with the high-low temperature cycling, and the microstructure and the mechanical properties of silicon rubber were measured at 336 h, 672 h and 1500 h respectively. Results showed that M/DBT molecules could diffuse into the silicon rubber, causing the swelling of silicon rubber. Meanwhile the precipitated additives from the silicon rubber together with the scission of Si-O-Si and Si-CH3 gave rise to the erosion surface morphology. The destruction of physical crosslink and the encouragement of chemical crosslink caused the first rising and then dropping of the total crosslink degree. Consequently, both the hardness and the tensile strength first went down and then went up with the ageing time going by, which reached the minimum value at 672 h. The increased hardness and degraded elasticity finally brought about the failure of the sealing ring.