EFFECTS OF PARTICLE-SHAPE AND SIZE DISTRIBUTIONS ON THE ELECTRICAL AND MAGNETIC-PROPERTIES OF NICKEL POLYETHYLENE COMPOSITES/

Electrical and magnetic properties of composite materials prepared by incorporating various nickel-based fillers of different shapes into po lyethylene were investigated. The fillers used were nickel powders, ni ckel filamentary powders, nickel flakes, and nickel-coated graphite fi bers. The particle-size distributions of the fillers were determined b oth before and after the processing of the composite samples. A wide r ange of filler volume fractions were used. In some cases, the volume f raction approached the maximum packing fraction of the solid phase to significantly exceed the percolation threshold. The composite samples were characterized in terms of their volume resistivity, dielectric co nstant, and magnetic permeability values. Filler particles of asymmetr ic shapes were very effective in terms of altering the electrical prop erties of the composite samples. At the highest loading levels of the nickel fillers, the volume resistivity values of the composites decrea sed by more than 17 orders of magnitude. At such high filler concentra tions, the dielectric constant values of the composite samples increas ed considerably, to values that were greater than 1000. The permeabili ty values of the samples increased linearly with the volume fraction o f the nickel filler and were insensitive to the shape of the fillers. The highest relative permeability value measured was 5.8 for composite s with 67% by volume of nickel powder. (C) 1993 John Wiley & Sons, Inc .