INFLUENCE OF FLAKE-LIKE GRAPHITE ON THE MICROTEXTURE OF MESOCARBON MICROBEADS

Mesocarbon microbeads (MCMBs) were prepared from a coal tar pitch without or with flake like graphite at 410?℃ for 7?h. The as received MCMBs were named MCB1 and MCB2 respectively and the MCB2 was divided into MCB2L and MCB2S according to the size of the flakes of graphite added. The surface and cross section of MCMBs were studied using SEM and the microtexture was analyzed by XRD. The surface of the MCMBs was rough with some particles attached and the beads are almost round. The microtexture of MCB1 (without graphite) was mainly of the parallel layer type, whereas the microtexture of MCB2 (with graphite) was complex. The large flakes of graphite added in the coal tar pitch were regarded as the centers of nucleation of MCMBs, resulting in hamburger type MCMBs (MCB2L), but the small ones could not act in this way in the reaction system, resulting in a distorted microtexture (MCB2S). It was proposed that when the nucleation occurred the large graphite flakes accumulated to form seed crystals in which the pitch components with low molecular weight were enwrapped and the shape and size of the flakes and their aggregations decided the microtexure of MCMBs, while the small graphite flakes served only to disorder the microtexture. The XRD spectra show that the addition of graphite decreased the graphitization degree and crystal sizes.