UV-VISIBLE AND NEAR-IR SPECTRA OF HEAT-TREATED PITCHES DURING MESOPHASE FORMATION

Heat-treatment processes of various pitches have been monitored by the UV-visible and near-IR spectra measured with the diffuse reflectance method. The shape and intensity of the observed absorption bands changed with the heat treatment of the pitches, reflecting the size of the aromatic molecules and the degree of the intermolecular interactions. For pitches exhibiting spherical mesophase and flow optical texture, some parts of the isolated aromatic hydrocarbons are converted into the agglomerates with lamellar structure by the heat treatment and both fractions are present in a considerable amount with proper ratio. On the other hand, in the case of pitch exhibiting the mosaic optical texture, the isolated aromatic hydrocarbons are unstable, converting to the disordered carbon.