PERCOLATION IN CARBON-BLACK POWDERS

The variation of conductivity and pressure transmitted by several carb on black powders is measured as a function of the solid volume fractio n during low-speed uniaxial compaction. For all samples made of aggreg ates, the experimental results of both pressure and conductivity can b e fitted with a percolation law. The percolation thresholds are, howev er, much smaller than the theoretical value phi() = 0.15. It is shown that the percolation threshold depends on the mass fractal dimension and on a length R(max) characteristic of the aggregates of a given car bon black.