Electrical conductivity of anthracites as a function of heat treatment temperature

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