Pressure dependence of the electrical resistivity of graphite powder and its mixtures

Using an experimental equipment which made possible electrical resistivity measurements of powders in dependence on pressure up to 250 kp/cm2, the relations between resistivity, pressure, and apparent density of graphite powder were investigated as well as the resistivity of graphite mixtures containing different portions of a non-conductive component. It is found that the electrical resistivity ϱ of graphite powder diminishes with pressure P according to the relation ϱ = k P−s. From the pressure dependence of the powder volume V, which is found to satisfy a relation of the same type, a contribution of 0.25 in the exponent s due to the packing of the particles has been determined applying Mrozowski's relation ϱ ∼ V3/4/P1/2 to the case of graphite. The relatively strong pressure dependence of the apparent density, as compared to carbon powders, is explained in terms of the greater orientation tendency of lamellar graphite particles, which is verified by orientation measurements. The pressure dependence of the electrical resistivity of graphite containing different portions of ZnO or SiO2 could be expressed by curves analogous to those for pure graphite but parallel shifted to greater resistivity values. The orientation of the graphite crystallites in compressed mixtures is considerably smaller than in pure graphite and decreases progressively with increasing content of the non-conductive component.