Degradation of polymer dielectrics with nanometric metal-oxide fillers due to surface discharges

Recent research has indicated that dielectric properties of polymer insulating materials might be improved by the inclusion of nanosized particles dispersed in the polymer matrix. Insulating materials in power apparatus are often exposed to surface discharges in the course of normal operation. Surface degradation due to continued exposure to such discharges may cause deterioration of the surface, and could ultimately lead to catastrophic failure. The current work investigates the effect of inclusion of nanometric particles on the ability of a polymeric dielectric to resist degradation when exposed to surface discharges. The dielectric material used was epoxy resin, while nanosized alumina (Al₂O₃) and titania (TiO₂) were used as fillers. Surface discharge tests were carried out on the specimens. The degraded surfaces were studied using a scanning electron microscope (SEM). Surface roughness measurements were made using a laser surface profilometer (LSP). It was observed that the degradation was greater for unfilled epoxy specimens than that for filled ones. Atomic force microscopy (AFM) and energy dispersive X-ray analysis (EDX) were used to identify surface changes in the dielectric material due to degradation. It has been conclusively shown that addition of even very small volume fractions of nanoparticles increases the resistance of the material to degradation due to surface discharges. A possible mechanism for surface degradation in nanocomposites has been proposed.