Electrical Resistivity of Partially Transformed Silicon Carbide Made from Coal

The bulk resistivity of coal that has been partially transformed to silicon carbide (SiC) over the temperature range 25-1600°C was investigated with an emphasis on temperature, SiC content, bulk density, and presence of elemental silicon. The materials were 0%SiC (wt%), 30%SiC, 69%SiC, and 72%SiC. Only the 72%SiC sample contained elemental silicon in substantial amounts. At low temperatures, there is high variation among all the materials, but at high temperatures the differences are less severe, as the results are all the same magnitude. The difference of the materials with the highest and lowest resistivity was around 30 mΩm between the 30%SiC and the 69%SiC at 1500°C. The mechanical strength of the material is lowered upon conversion to SiC but is raised once elemental silicon begins to form. In addition to temperature, the resistivity seems to respond to SiC content, bulk density, and the presence of silicon. An increase in bulk density consistently leads to a decrease in the resistivity, except with the presence of silicon. SiC content may have some effect, but it is lesser compared to the other factors examined so far.