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

The carbonization behaviors of a series of synthetic naphthalene-derived 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 thermal volatilization analysis (TVA/SATVA). Qualitative and quantitative analysis of the carbonization products was made using a combination of gravimetric and FT-IR techniques. It was concluded that an ''ideal'' oxidation profile could be defined alternatively in terms of the relative magnitude of the product fractions from carbonization, rather than in terms of a specific time/temperature profile of oxidation. Mechanisms are suggested to explain the carbonization behavior of both unoxidized and oxidized mesophase pitches. It was also concluded that the melting and fusion associated with the carbonization of previously unoxidized or insufficiently oxidized pitch is accompanied by the production and subsequent rearrangement, migration, and recombination of relatively large quantities of oxygen free aromatic radicals. In contrast, the dimensional stability associated with sufficiently oxidized pitches can be attributed to concerted decarboxylations of ester and anhydride crosslinks, which result in ''caged'' aromatic radicals that are advantageously positioned for recombination without migration or rearrangement.