Analysis and modeling of mesophase sphere generation, growth and coalescence upon heating of a coal tar pitch

Abstract

The present study has been undertaken aiming: (1) to provide an experimental procedure for measurement of characteristics of mesophase sphere formation from a coal tar pitch upon heating at 673–723 K in terms of the time-dependent changes in the population density and the radius distribution of the spheres and (2) to prove that the nucleation, growth and coalescence of the spheres are essential for quantitative explanation of the time-dependent changes. In regard to (1), this paper describes the conditions that are required in microscopic analysis of cross-sections of the bulk of heat-treated pitch for the conversion of the population density and the radius distribution of the cross-sectional circles into those of spheres on volume basis. Regarding (2), a model analysis demonstrates that the change in the radius distribution with time, as well as that in the population density of spheres, can quantitatively be predicted. The analysis also reveals that the spheres grow without undergoing coalescence in the early period, and the sphere coalescence commences after termination of sphere generation while the growth continues.