Formation of Mesophase Spheres in a QI-Free Coal Tar Pitch

A QI-free coal tar pitch prepared by solvent extraction from a soft coal tar pitch was subjected to a series of thermal treatments at a predetermined temperature for different holding times. The development of mesophase was discussed in terms of its size and content in the heat-treated pitches. Results showed that the size and yield of the dispersed mesophase spheres in the isotropic matrix strongly depended on the holding temperatures. When the holding temperature was less than 400 °C, only a few of small spheres formed in the mesophase pitches. However, when the holding temperature was over 420 °C, the diameter and yield of mesophase spheres in the heat-treatment pitches increased progressively with increase of the holding time. Treatment at 440 °C for 4h led to 19.9 % of the yield and the average sphere radius was 4.5-100 . In the SEM photograph of mesocarbon microbeads obtained from the heat-treated pitches using soxhlet extraction. Many small flaky particles and sporadic rugby ball-shaped particles were observed as well as a large number of spherical particles.