The electrical performance of polymeric insulating materials under accelerated aging in a fog chamber

A comparative study of the AC (60 Hz) surface aging in a fog chamber is reported on cylindrical rod samples of high-temperature vulcanized (HTV) silicon rubber and ethylene propylene diene monomer (EPDM) rubber containing various amounts of alumina trihydrate (ATH) and/or silica fillers. In low-conductivity (250- mu S/cm) fog, silicone rubber performed better than EPDM samples, whereas in high-conductivity (1000- mu S/cm) fog, the order of performance was reversed. The mechanisms by which fillers impart tracking and erosion resistance to materials is discussed as influenced by the experimental conditions of the accelerated aging tests. Surface studies by ESCA (electron spectroscopy for chemical analysis) demonstrate that the hydrophobicity of silicone rubber, despite the accumulation of surface contamination, can be attributed to migration of low-molecular-weight polymer chains and/or mobile fluids, such as silicone oil.< >