Two types of mesocarbon microbeads(MCMB), one of which was green sphere and the other carbonized at 1000 ℃, were used to modify coal tar pitches, and their influences on the development of carbonaceous mesophase in coal tar pitches were investigated. Optical microscopy was used to observe the changes caused by the additives. The green MCMB could promote the growth of mesophase spheres. When the holding time at the final temperature was prolonged to 100 min, the green MCMB-modified pitch would produce excellent bulk mesophase. Carbonized MCMB prohibited the coalescence of mesophase spheres and was beneficial to forming super large mesophase spheres. In the green MCMB-modified pitch, mesophase spheres grew up using the added MCMB spheres as nuclei, i.e. the green MCMB continued to grow during heat-treatment, which accelerated the formation, growth, and coalescence of mesophase spheres. For carbonized MCMB, their active sites were passivated and they could not continue to grow. These inert spheres could aggregate around the newly-formed mesophase spheres, prohibiting the growth and coalescence of the mesophase spheres.
