Microstructure of mesocarbon microbeads prepared from synthetic isotropic naphthalene pitch in the presence of carbon black

Mesocarbon microbeads (MCMB) prepared from a synthetic naphthalene isotropic pitch with or without carbon black were compared in their microstructure observed under high resolution scanning electron microscopy and transmission electron microscopy (TEM). The spheres prepared without carbon black exhibited an assemble of microdomain units with a number of voids among the units after isolation by pyridine extraction. In contrast, the spheres prepared in the presence of BP2000 and Ketjen Black with a chain structure had smooth surfaces covered with carbon black particles. TEM showed the dispersion of chain particles in the inside of the sphere as well as some shell skin 50-200 nm in thickness surrounding the sphere. MA600 of non-chain structure was found to be distributed on the surface and the inside of the sphere, however, isolated microdomains were observed on the surface of the sphere with a number of voids. MCMB are produced through a series of steps: the formation of mesogen molecules; the formation of insoluble microdomains; the assembly of microdomains into spheres; the incorporation of a soluble fraction in the sphere; and the phase separation of spheres in the isotropic matrix. The particles on the surface form the shell with mesogens which are almost insoluble in pyridine. The chain structure appears to the key to the formation of such a shell. Another portion of carbon blacks stays in the matrix, increasing its viscosity preventing the coalescence and precipitation of spheres and suspending their dispersion in the matrix.