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.