The authors introduced an ultrasonic technique as a method to investigate the process and/or rate of growing and developing of mesophase with heating. Two kinds of pitches were chosen for this purpose i.e., synthetic naphthalene pitch (MC) and hydrogenated coal-tar pitch (HC). In addition, solvent extraction analysis, polarizing optical microscope observation and rheological data were also used to help understand the ultrasonic data. For pitches of MC and HC, two peaks on the curve of the attenuation coefficient related to appearance and development of mesophase were observed against heating time at 330°C and 380°C, respectively. Thus, it was found that the investigation of pitches by means of their ultrasonic observation leads to a good description of appearance and development of mesophase during heating treatment. Consequently, it is expected that the ultrasonic method will be useful in examining the in situ observation for appearance and development of meso-carbon microbeads.
