Influence of additives on the permeability of impregnating coal-tar pitch

Coal-tar pitch is widely used to prepare composite materials by the several cycles of impregnation and carbonization. Impregnation becomes the control step for cost when the high-density carbon preform is densified. Thus, effects of additives on the permeability of the pitch are investigated by experiments and their mechanisms are discussed according to theoretical analysis of fluid kinetics. Direactive glyceride as well as aluminum sulfate and polyethylene oxides evidently increase permeability by changing the physical structure of pitch. However, divinylbenzene has chemical modification to the pitch in the presence of p-toluene sulfonic acid, which leads to a marked decrease in permeability. In this regard, the former two types of additives are more suitable than the latter one to modify the coal-tar pitch as a precursor to densify the carbon preform with high density. In addition, the permeability drastically depends on the concentrations of additives.