Simple method for characterizing synthetic graphite powders

Publisher Website
Google Scholar
Abstract
A simple method for characterizing synthetic graphite powders is presented in this paper. A thick glass cylinder contains a known weight of material, which 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 variation are simultaneously measured. From these results, the relation between conductivity and the volume fraction of grains is derived: an equation based on the effective medium theory (EMT) is shown to fit the experimental data accurately. The adjustable parameters are directly linked with both the anisotropic conductivity and the morphology of the grains. On the one hand, conductivity 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 obtained from apparent density measurements. The percolation thresholds which would be expected from composites made of graphite powders imbedded in an insulating medium are also calculated via the EMT equation. Comparison with other theoretical and experimental values always leads to very good agreement, showing the accuracy of the EMT equation in supplying fair geometrical parameters for the particles.