Mitsuhiko Koyama

Dielectric property of composites made with polyethylene, boron nitride and carbon black

The dielectric breakdown strength of the composite with a boron nitride as an insulating filler and/or a carbon black as an electrically conductive filler was measured and discussed from the view of percolation phenomena. The dielectric breakdown strength decreases with increasing the volume of carbon black. It is dominated by finite clusters of a carbon black and is not influenced by a boron nitride. The dielectric breakdown strength is described by a function of a power law of the distance from the volume fraction of carbon black to the percolation threshold with the critical exponent of /spl nu/ = 0.9. And it was found that the percolation threshold of the composite with a carbon black and a boron nitride was larger than that of the composite with a carbon black.

Fiber reinforced epoxy casting resin as an insulating material for high voltage application

It is well known that glass fiber addition into resin will increase the resin viscosity. However, such a viscosity increase did not occur at all when fine particles several micrometers in size were used in combination with the fibers. On the basis of this phenomenon, the authors have developed and applied successfully a new type of casting resin that is reinforced by glass fiber. In this paper, the reason that the resin viscosity does not increase when adding fine particles in combination with the fibers into the resin is discussed.