Rheological properties and carbonization of coal-tar pitch

During the carbonization of coal-tar pitch the viscosity of the pitch decreased at 200-360 degrees C, reached a minimum at 360-400 degrees C, and then increased at 400-450 degrees C. The decrease of the viscosity of the pitch after its melting may be attributed to the solubilization of benzene insolubles (BI) (beta-resin and quinine insolubles) by the solvation of benzene solubles (BS) to BI, in addition to the increase of thermal movements of pitch with increasing temperature. The viscosity increase above 400 degrees C can be explained by the growth of a high molecular weight mesophase. The addition of extra beta-resin to the pitch resulted in the formation of smaller anisotropic domains, compared with the carbonization of the pitch alone. beta-Resin seems to become nuclei for thermal condensation, leading to the rapid solidification of the mesophase. This hinders the growth of the mesophase to a large anisotropic domain.