Characterization of pitches by an ultrasonic method: Change in the molecular aggregation state during air-blowing

The air blowing reaction has been used to modify the chemical structure and molecular aggregation of pitches for general-purpose carbon fiber on an industrial scale. The purpose in this study is to obtain fundamental ultrasonic data so that one can monitor in situ the change in chemical structure and molecular aggregation state in air blowing reaction. For this purpose, the effects of heat-treatment, oxygen (or air), and distillation (or low pressure) on the ultrasonic properties were separately examined. It was found that the ultrasonic measurements give the temperature dispersion curve characteristic to the structure, which was quite consistent to previous studies by ESR and NMR.