Mechanical and thermal properties of heat treated coals

Abstract

Studies of the Brinell and Shore hardness, of the compressional and transverse mechanical strength, the dynamic Young's modulus, the thermal expansion coefficient and of the thermal conductivity were carried out on coal carbon solids as a function of heat treatment temperature (HTT). The coal carbon compacts were made from Akabira weakly-caking coal (d.a.f. C = 83.4%) and from Itmann strongly-coking coal (d.a.f. C = 90.2%) powders by compressing them at room temperature without binder to 1000 and 2000 kg/cm 2. The values of Brinell hardness, of the mechanical strength and of the dynamic Young's modulus increase up to a maximum at HTT 1000–1200° and then decrease with increase of HTT, but the Shore hardness shows two maxima in the range from HTT 500° to HTT 3150°C. The mechanical strength of coal carbon solids is higher than the ordinary pitch-bonded carbon solids. It is believed that this is due to the rigid bonding of coal carbon particles which occurs in the carbonization process. The thermal expansion coefficient for Akabira-coal carbon solids at first decreases with the increase of HTT, shows a minimum at HTT about 1600°C and increases with HTT. The thermal conductivity for Akabira-coal carbon solids increases with increase in HTT. A good correlation between the thermal and the electrical conductivities has been found.