Optical mesophase texture and X-ray diffraction pattern of the early-stage carbonization of pitches

Abstract

Low temperature carbonization of pitches was studied with polarized-light microscopic method, X-ray diffraction, solvent extraction and density measurements. The nucleation and growth of spherical bodies occur progressively with increase of residence time at a fixed temperature, until the spherical bodies eventually coalesce with each other. Fine irregular particles of insolubles in coal-tar pitch are observed in the region of boundary between spherules and matrix. They play an important role in the mesophase transformation. The typical changes of stacking height of lamellae, interlamellar spacing, weight loss, density and insolubility with residence time show nearly the same tendency at the various temperatures from 390° to 430°C. The time-temperature superposition has been successfully employed. In the master curve for coal-tar pitch reduced at 410°C, the reduced time scale extends from 10 −2 to 10 2 hr. From the relation between the reducing factor of time translation and absolute temperature, the apparent activation energies can be estimated over the range of 35–45 kcal/mole. It seems probable that a model of the rearrangement of C—C bonding together with vaporization of low molecular substances is applicable for the growth of spherical bodies.