On surface degradation mechanisms of epoxy filled with Silica nanoparticles caused by partial discharges

Silica (SiO₂) filled epoxy with a particle size in μm-range has been established during the last decades. Now it has become possible to produce SiO₂-filled epoxies, with filler particles in nm-range, which can be located in the polymer homogenously and without agglomerates. A new group of materials with a high percentage of inner boundaries has been designed. Therefore, the effect of this high interface to volume ratio on the performance profile of the composite has to be analyzed. This paper presents surface degradation results of epoxies with nanoscale (nm) SiO₂ fillers (d₅₀ = 23nm) with filler amounts of 26 and 44 wt%. The test item consists of a 1 mm thick plate with a polished surface, which is stressed with partial discharges (pd). The pd-energy is calculated and the eroded volume on the surface of the stressed epoxy is determined. The eroded surface is analyzed with SEM and AFM, which visualizes a nm-structured coating with a high ratio of SiO₂ nanoparticles. Additionally, the surface resistance change during the pd-stress of the SiO₂-filled epoxies is shown by a comparative analysis related to the materials. A research of the possible degradation mechanism of nm-filled epoxy compared with standard neat and μm-filled (μm) epoxy is presented.