Dielectric Strength Of Al2o3/Silicone Composites After High-Temperature Aging

Silicones are widely used for electrical insulation owing to their high dielectric strength and thermal stability. However, recent studies revealed insufficient stability of silicone for high-temperature applications. To study the effect of Al2O3 fiber on silicone stability, we measured the dielectric strength of unfilled silicone and Al2O3/silicone composites as a function of aging time at 250 degrees C in air and analyzed data by Weibull probability distribution to determine characteristic dielectric strength (E-0) and shape parameter (beta). Prior to aging, unfilled silicone and composites had similar behavior, with E-0 at about 20 kV/mm and beta > 15. During aging, unfilled silicone developed both micro-and macrocracks, with beta dropped below five in 240 h and E-0 decreased significantly. Composites developed microcracks, with beta dropped below 5 in longer time and E-0 remained almost constant. Addition of Al2O3 slowed down crack growth in silicone matrix, resulting in longer lasting high-temperature dielectric materials. (C) 2014 Wiley Periodicals, Inc.