Propagation of acoustic waves in pitch

The speed of ultrasound in coal pitch is investigated as a function of the quantity of α 1 fraction and the pitch temperature. It is found that the speed of the ultrasound increases with increase in the quantity of α 1 fraction. The type of pitch determines the specifics of the actual dependence. The temperature dependence of the speed of ultrasound in pitch has distinct points of inflection, indicating rheological transitions in the pitch on heating. The effective activation energy of the rheological transitions is calculated. There is a discrepancy between the softening temperature of the pitch and the transition temperature to the fluid state. The transition temperature to the fluid state measured by means of ultrasound may be used as a technological parameter of the pitch.