Changes of Microstructure and Properties of Manufactured Modified Pitches via Pressure Changes during Heat Treatments in Coal Tar Pitch

Abstract

Coal-tar pitch, a feedstock which can be heat-treated to create graphite, is composed of very complex molecules. Coal-tar pitch is a precursor of many useful carbon materials (e.g., graphite, carbon fibers, electrodes and matrices of carbon/carbon composites). Modified coal-tar pitch (MCTP) was prepared using two different heat-treatment methods and their properties were characterized and compared. One was prepared using heat treatment in nitrogen gas; the other was prepared under a pressure of 350 mmHg in air. The MCTPs were investigated to determine several properties, including softening point, C/H ratio, coke yield, formation of anisotropic mesophase and viscosity. The MCTPs were subject to considerable changes in chemical composition due to condensation and polymerization in the used-as-received coal-tar pitch after heat-treatment under different conditions. The MCTPs showed considerable increases in softening point, C/H ratio, and coke yield, compared to those of as-received coal-tar pitch. The MCTP formed by heat-treatment in nitrogen showed isotropic phases below <TEX>$350^{\circ}C$</TEX> for 1 h of soaking time. However, MCTP heat-treated under high pressure (350 mmHg) showed isotropic phases below <TEX>$300^{\circ}C$</TEX>, and showed anisotropic phases above <TEX>$350^{\circ}C$</TEX>, for 1 h of soaking time. The viscosity of the MCTPs increased with increase in their softening points.