ELECTRICAL-RESISTIVITY OF CARBONIZED COALS

The aim of the study was (i) to determine the relationship between the end temperature of carbonization (ETC) and electrical resistivity of the carbonized coals and (ii) to find a minimal ETC which is satisfact ory with regard to yielding low-resistivity (<0.25 ohm/cm) coke rods t hat could be used for fullerene preparation. Twenty-seven coals, 82-92 % C daf, were studied. Coal samples were heated to various ETC in the 650-850 degrees C range. Electrical resistivities of the resultant cok e rods were measured exclusively at ambient temperature. Ultimate and proximate data as well as content of optically anisotropic phase were determined for selected coke rods. A rapid falloff of the resistivity, from 10(3) to 1-3.6 ohm/cm, was found on increase of ETC from 650 to 750 degrees C. Further ETC increase to 850 degrees C led to a moderate resistivity decrease to 0.1-0.3 ohm/cm level. A formula was worked ou t that defined the relationship between concentration of electrical cu rrent carriers in the coke rods and the end temperature of carbonizati on. The Arrhenius thermal coefficients for various coals were 480-740 kJ/mol and 200-290 kJ/mol for ETC <750 degrees C and ETC >750 degrees C, respectively. Resistivities of the cokes and individual aromatic co mpounds were compared. This led to a conclusion that a network of coke basic aromatic units plays an important role in generating electrical current carriers.