The rheological behavior during carbonization of iodine-treated coal tar pitch Original Research Article

Changes of rheological properties, especially thermal fusibility, during carbonization processes of iodine-treated coal tar pitches have been investigated by TG–Mass, viscometer and proton nuclear magnetic resonance thermal analysis. It was found that iodine could exist in two distinct forms in coal tar pitch (CTP). Introduced iodine molecules, about 30 wt% against the CTP, formed charge-transfer complexes with the CTP molecules. These charge-transfer complexes decompose at temperature above 200°C to form HI and free radicals, which promote cross-linkage and reduce the resolidification temperature of CTP by two hundred degrees. Additional iodine (at levels of greater than 30 wt%) could be eliminated by ethanol and be weakly bound to the CTP. Over extended periods of time at 100°C, latter form of iodine increases the softening temperature and viscosity of the CTP, possibly by acting as an oxidant. The combination of the two effects explains how iodine is so effective as a stabilizer of CTP.