Thermal Aging Characteristics of Silicone Rubber Exposed to Mineral Oil

Abstract

Room temperature vulcanized (RTV) silicone rubber is extensively utilized as a coating material for power transformer bushings because of its high hydrophobicity and excellent anti-pollution flashover resistance. However, the performance of silicone rubber may suffer significantly when exposed to mineral oil. Till now, literature available on understanding the degradation behavior of silicone rubber exposed to mineral oil at different temperatures is very rare. Therefore, in the present work oil immersion test is performed. RTV silicone rubber was thermally aged in mineral oil at 40°C and 80°C for 200 hours. Post ageing, to examine the changes in the surface properties of the aged specimens 3D microscopy, scanning electron microscopy (SEM) analysis, contact angle, proof tracking index (PTI), and shore hardness measurements were made. The results indicate that the degree of surface degradation was proportional to the temperature. Further, thermogravimetric analysis (TGA), differential thermal analysis (DTA), and infrared thermography were employed to evaluate the thermal properties of aged and unaged specimens. TGA-DTA and infrared thermography indicated a remarkable reduction in thermal stability and heat dissipation capability post mineral oil ageing. The effect became more adverse with increasing ageing temperature. Also, ageing resulted in a decrease in alternating current (AC) breakdown voltage and PTI. Finally, all the experimental outcomes were correlated and the degradation dynamics of mineral oil-aged silicone rubber are explained in detail through possible chemical reactions, fourier transform infrared (FTIR) spectroscopy and energy dispersive X-ray spectroscopy (EDAX) investigations.