Effects of interfacial phenomena on dielectric breakdown of filled epoxy resin

Dielectric properties, the frequency characteristics, space charge distribution and dielectric breakdown strength of filled epoxy resins were measured after water attack at 50/spl deg/C. The loss tangent tan /spl delta/ of these composites showed a tendency to increase rapidly, but roundish filled resin did not show the phenomena to increase rapidly, and this tan /spl delta/ increased only a little. The same was true of the case that space charge distribution and dielectric breakdown strength were measured after water attack at 50/spl deg/C. That is to say, in square silica filled resins hetero-space charge was formed near the anode and the cathode. Dielectric breakdown of roundish silica filled resin was on a higher plane in comparison with square silica filled resins. The conducting meshes were formed along the interfaces between filler and epoxy resin. We could obtain lower loss tangent epoxy resin castings through the roundish silica filler.