THE OXIDATIVE STABILIZATION AND CARBONIZATION OF A SYNTHETIC MESOPHASE PITCH .2. THE CARBONIZATION PROCESS

The carbonization behaviors of a series of synthetic naphthalene-deriv ed mesophase pitch powders subjected to different time and temperature profiles of oxidative stabilization were studied by thermogravimetric analysis (TGA) and thermal volatilization analysis/sub-ambient therma l volatilization analysis (TVA/SATVA). Qualitative and quantitative an alysis of the carbonization products was made using a combination of g ravimetric and FT-IR techniques. It was concluded that an ''ideal'' ox idation profile could be defined alternatively in terms of the relativ e magnitude of the product fractions from carbonization, rather than i n terms of a specific time/temperature profile of oxidation. Mechanism s are suggested to explain the carbonization behavior of both unoxidiz ed and oxidized mesophase pitches. It was also concluded that the melt ing and fusion associated with the carbonization of previously unoxidi zed or insufficiently oxidized pitch is accompanied by the production and subsequent rearrangement, migration, and recombination of relative ly large quantities of oxygen free aromatic radicals. In contrast, the dimensional stability associated with sufficiently oxidized pitches c an be attributed to concerted decarboxylations of ester and anhydride crosslinks, which result in ''caged'' aromatic radicals that are advan tageously positioned for recombination without migration or rearrangem ent.