Influence of Particle Size on the Electrical Resistivity of Compacted Mixtures of Polymeric and Metallic Powders

Powder samples of high-density polyethylene and nickel of particle sizes Rp and Rm, respectively, were mixed and compacted at room temperature under a pressure of 1000 kg/cm2. Microscopic examination of polished sections of the compact, by reflected light, showed that the metallic particles did not penetrate the polymeric particles and that this resulted in a segregated distribution of metallic particles at high ratios of Rp/Rm. The electrical resistivity of the compacts had a value of 1016 Ω cm unless the composition of metal reached a critical value, beyond which the resistivity decreased markedly by as much as twenty orders-of-magnitude. This critical composition was found to decrease with an increase in the ratio Rp/Rm throughout the range studied of from 1 to 16. The general features of the dependence of electrical resistivity on composition of metal could be rationalized by reference to a model according to which small particles of nickel form a monolayer on the large particles of polymer in the mixture of powders. This arrangement was supposed to be but little changed during compaction and to result in a segregated distribution of metal which can be visualized as approximating to the accommodation of metallic particles on three mutually perpendicular sets of lattice planes. The critical composition for a sudden decrease in electrical resistivity was assumed to correspond to the first nonzero probability for infinitely long chains of contiguously occupied lattice sites.