Formation of mesophase spheres from a coal tar pitch upon heating and subsequent cooling observed by an in situ 1H-NMR Original Research Article

Coal tar pitch was heated at a rate of 10 K/min up to 723 K in an atmospheric flow of nitrogen gas, soaked at the temperature for time, tH, ranging from 0 to 480 min. A microscopic observation revealed that soaking for tH shorter than 120 min produced dispersed mesophase spheres, while longer soaking resulted in a flow-textured mesophase due to a progress of coalescence of the spheres. Diameter and yield of the dispersed spheres depended on the rate of cooling, suggesting that the spheres formed upon cooling. In situ proton nuclear magnetic resonance (1H-NMR) detected three components, G1, G2 and W having different transverse magnetization decays, in the pitch upon soaking. Magnetization decays of G1 and W agreed well with those of meso-carbon microbeads (MCMB) and fully fused isotropic pitch, respectively. When tH was shorter than 60 min, no G1 was detected while spheres were observed in the pitch after cooling, confirming mesophase formation upon cooling after soaking. It was also found that the formation of spheres upon cooling accompanies the complete conversion of G2 into G1 and that the G1 formed hardly fuses while reheated to 723 K.