XRD and 29Si MAS NMR spectroscopic studies of carbon materials obtained from pyrolyses of a coal tar pitch modified with various silicon-bearing additives

A typical coal tar pitch used in manufacturing of graphite electrodes was individually modified with various silicon-bearing additives yielding mixtures that were pyrolyzed (carbonized) stepwise at increased temperatures up to 1650 °C. Three commercially available additives such as the elemental Si, silica SiO2, and poly(carbosilane) {–CH2–SiH(CH3)–}n as well as reference silicon carbide SiC were used. The resulting intermediate and final materials were studied with the XRD and 29Si MAS NMR methods. For two additives, i.e., elemental Si and poly(carbosilane), the beginning of their conversion to SiC was detected at 1300 °C while for SiO2 higher temperatures were required under applied conditions.