Dielectric strength of Al sub(2)O sub(3)/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 Al sub(2)O sub(3) fiber on silicone stability, we measured the dielectric strength of unfilled silicone and Al sub(2)O sub(3)/silicone composites as a function of aging time at 250 degree C in air and analyzed data by Weibull probability distribution to determine characteristic dielectric strength (E sub(0)) and shape parameter ( beta ). Prior to aging, unfilled silicone and composites had similar behavior, with E sub(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 sub(0) decreased significantly. Composites developed microcracks, with beta dropped below 5 in longer time and E sub(0) remained almost constant. Addition of Al sub(2)O sub(3) slowed down crack growth in silicone matrix, resulting in longer lasting high-temperature dielectric materials.