Enhancement of electrical, mechanical and thermal properties of silicone based coating with aluminatrihydrate/silica for ceramic insulators
Israr Ullah, M.S. Akbar, Haris Ahmad Khan
Abstract
The present work explores durability enhancement in various properties of room temperature vulcanized silicone rubber (RTV-SiR) coating with the incorporation of alumina trihydrate (ATH) and silica (SiO2) fillers. Test samples i.e., neat RTV-SiR, RTV-SiR +10% μSiO2, and RTV-SiR filled with micro-ATH/SiO2 (10% each) were chosen for experimentation. Long-term (10,000 h) lab aging of composite coatings is performed under bipolar direct current (DC) voltage with simulated environmental stresses in a test chamber. The effect of fillers against stresses is quantified through characterization results comparison of filled composites with unfilled RTV-SiR samples. Moreover, the polarity effect on degradation is evaluated through the relative performance of each composite under the positive and negative polarity of the voltage. Findings revealed that samples filled with a mixture of additives bring enhanced improvement into the base matrix of RTV-SiR. Amongst unfilled and micro-silica filled specimens aged under positive DC, the samples S-3 with combined silica-ATH fillers offered superior hydrophobic behavior showing hydrophobicity class HC3 and demonstrated a minimum final leakage current of 6.13 μA. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) results showed relatively lower variations in the chemical and morphological structure of cross-filed specimens (S-3). Furthermore, results of mechanical properties (tensile strength, elasticity, and weight) show a significant loss, whereas the hardness of composite increased with aging. Hybrid samples (S-3) exhibited the minimum deviation of 29.77% and 43.12% in tensile strength and elongation-at-break (EAB), respectively under positive DC voltage. Similarly, it shows enhanced resistance against weight loss and change in hardness due to aging. Moreover, thermogravimetric analysis (TGA) confirmed that filled composite gets enabled to offers the least alteration in thermal properties. In the context of the polarity, positive DC voltage incurred more devaluation of desirable properties as compared to negative polarity.