Preparation, electrical resistivity and its temperature dependence of RuO₂-polystyrene composite powder

Abstract

RuO₂-polystyrene composite powder was prepared by admixing fine powdered RuO₂ and polystyrene beads thoroughly in ethanol. RuO₂-coated polystyrene beads were also prepared by direct suspension polymerization of styrene in an aqueous phase in the presence of a suspended RuO₂ powder. The apparent d.c. volume resistivity,ρa, of the hot-pressed composite was measured at various temperatures (20 to 80° C), pressures (3.5 to 35 MPa) and volume fractions of RuO₂,φ, (0.008 to 0.10). The volume resistivity increased linearly with temperature on a double logarithmic scale. The equilibrium volume resistivity at constant temperature,ρaT, decreased remarkably whenρ increased from 0.025 to 0.04 for the mixed material, due to the establishment of a continuous network of RuO₂ in this region, as revealed by scanning electron microscopy. The composite prepared by direct polymerization completed a network of the conductive phase at a much smaller volume fraction of RuO₂. The average size of RuO₂ aggregates covering the surface of polystyrene agreed fairly well with the calculated value based on the simple geometry.