Simple method for characterizing synthetic graphite powders

A simple method for characterizing synthetic graphite powders is presented in this paper A thick glass cylinder contains a known weight of material, w hich is held between two conducting pistons. These allow the measurement of the electrical conductivity of the sample, and enable its compaction. The graphite powder is gently pressed, and its volume and conductivity variatio n are simultaneously measured. From these results, the relation between con ductivity and the volume fraction of grains is derived: an equation based o n the effective medium theory (EMT) is shown to fit the experimental data a ccurately. The adjustable parameters are directly linked with both the anis otropic conductivity and the morphology of the grains. On the one hand, con ductivity measurements achieved on single particles give values of the same order of magnitude as those derived from the fits. On the other hand, the other parameters of the equation perfectly agree with the aspect ratios obt ained from apparent density measurements. The percolation thresholds which would be expected from composites made of graphite powders imbedded in an i nsulating medium are also calculated via the EMT equation. Comparison with other theoretical and experimental values always leads to very good agreeme nt, showing the accuracy of the EMT equation in supplying fair geometrical parameters for the particles.