Surface resistance of epoxy/BN micro- and Meso-composites exposed to electrical discharges

Boron nitride (BN) has shown in the past to improve DC breakdown strength as well as augmenting thermal conductivity. Two different filler sizes, one micrometric with an average particle size of 9 μm and a sub-micrometric one, 0.5 μm in size, have been used to form composites. The amount of each type of BN in the matrix has been varied from 1 to 5 wt%. The samples have been exposed to electrical discharges using a point-to-plane geometry operated in open air. The experiment was conducted at an enhanced frequency of 300 Hz to accelerate the erosion process. The surface erosion has been evaluated after several distinct time steps using a mechanical profilometer. It has been found that introducing BN into epoxy decreases the amount of eroded volume of the organic matrix with decreasing filler amount. In addition, micrometric BN composites performed better than their sub-micrometric counterparts. The dielectric response has been evaluated using broadband dielectric spectroscopy (BDS) at 20°C before the erosion, as well as after each time step. An increase of dielectric losses at very low frequencies for all samples after erosion has been observed, accompanied by a slight increase in real permittivity. Besides the β-peak, the formation of an additional loss peak, located around 1 Hz, has been found.