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A fluid DGEBA/methyl nadicanhydride epoxy system has been filled with inorganic particles, cast as bubble-free plates and cured. The ability of both the pure network polymer and the polymer/particle composites to withstand partial electrical discharges has been investigated. Three types of particle combinations were used: (a) fumed nanoparticle silicon dioxide referred to as Aerosil, (b) equal volumes of Aerosil and nanoparticle anatase, and (c) Aerosil plus anatase in combination with coarse-particle filler grade calcium–magnesium carbonate dolomite. A test for endurance using the CIGRE method II electrode arrangement was applied, the test comprising the establishment of partial discharges running perpendicularly onto one face of a plate specimen for a period measured until breakdown Our results show that the endurance of the pure polymer is low. Increased loading with Aerosil increases the endurance by a factor of up to 20 as the Aerosil content goes from zero to 5.4 vol.%. Aerosil mixed with anatase has a similar effect. The high level of endurance is maintained with an additional high-volume (35 vol.%) filling of coarse-particle dolomite to an epoxy system already containing Aerosil and anatase. The results are discussed in the light of estimated interparticle spacings and interface areas.
Henk et al. (Wed,) studied this question.