Electrical conductivity of anthracites as a function of heat treatment temperature

The electrical conductivity of various kinds of charred anthracites has been systematically studied as a function of their heat treatment temperature. Concurrently, volume and mass variations of several samples of these materials were measured after each calcination. From these results and based on a simplified picture of the structure of ideal anthracites, we propose to quantitatively explain the thermal variations of their conductivity. With this aim in view, we refer to a percolation of conducting pseudo-graphitic microcrystallites. Within the raw materials, these latter are initially bordered with volatilizable organic groups: as the heat treatment temperature progressively rises, a growing amount of volatile substances is removed from the material. making the conducting units to come into intimate contact with each other. The relevance of this model seems confirmed by the fact that a conductivity law quantitatively consistent with percolation theory predictions is observed in each kind of studied anthracite. (C) 2000 Elsevier Science Ltd. All rights reserved.