Mesophase powders (carbonization and graphitization)

Abstract

Four mesophase powders, A, B, C, and D, are studied. A is petroleum derived, B, C, and D are commercialized powders and are coal-tar derived. No additives are recognized in A, which is almost devoid of cross-linking oxygen. In B, a thin deposit (~100 nm) of a phase, which appears isotropic in transmission electron microscope (TEM), surrounds the spheres and the primary quinoline insoluble (QI). C and D are increasingly altered. The altered areas of C surround a core of residual mesophase sphere with a thickness up to 1 μm. D, the powder richer in oxygen, is entirely altered. By aging, B becomes similar to C, whereas C is transformed in a matrix of alteration, including relics of spheres. After carbonization and heat treatment (HT) at 2800°C, A is entirely lamellar and strongly graphitized. B, C, and D contain a decreasing amount of lamellae and an increasing amount of pores of decreasing size. They have a decreasing ability to graphitize. The increasing alteration is assumed to be due to the occurrence of adsorbed heavy solvents. They act as dispersing agents on the basic structural units (BSU). Correspondingly, mesophase spheres regress down to local molecular orientations (LMO), which decrease in size as solvent alteration progresses.