Characterization of Structural Change during Carbonization of Coal-tar Pitch

Abstract

Coal-tar pitch was heat-treated at various temperatures up to 1000°C and the weight loss (Δw/w) measurement, CHN analysis, polarized-light microscopic observation, IR and ESR spectra, and X-ray diffraction study were done. These data gave us the feature of structural change of coal-tar pitch through carbonization reaction, especially the change which occurred in the temperature range of pitch solidifying was remarkable. The behavior of structural change varied with the heat-treatment temperature (HTT) 500-600°C as a border. At HTT 600°C the bulk mesophase was formed completely and absorption bands except aromatic rings disappeared in IR spectrum, and the value of interlayer spacing showed for a typical disoriented carbon, that was 3.44A. The radical concentration (N) was the maximum at this HTT 600°C.By plotting log N against Δw/w, a linear relationship was observed. This relationship suggests that the amount of released components is in proportion to the amount of breaking hydrocarbon chains, and it brings the radical formation.