Ultrasonic Study of Critical Mixing of n-Heptane and Nitrobenzene

Abstract

The sound attenuation (1∼9 MHz) and velocity in the critical mixture, n-heptane-nitrobenzene, have been measured in detail through the critical mixing temperature at 1 atm by the pulsed technique which incorporates the pulse-echo-overlap method and signal-averaging. Temperature and frequency dependence of the critical attenuation per wavelength α_λ(crit.) and dispersion have been examined in terms of the mode coupling theory by Fixman and Kawasaki. The results support the analogy of sound propagation in the critical fluid states of gas-liquid and liquid-liquid. Possible behavior of the zero-frequency sound speed c₀ is also discussed.