EXPERIMENTAL-STUDY OF PHASE-TRANSITIONS IN MERCURY

The results of sound velocity measurements in mercury, performed at temperatures from 300 up to 2050 K and pressures from 30 up to 1900 bar by a precise pulsed phase-sensitive technique for a frequency of 10 MHz, are presented. The explored range of state parameters includes liquid and gaseous phases, the coexistence curve up to the critical point, and the supercritical region. The data obtained indicate the existence of two first-order phase transitions in mercury that take place in the vapor near saturation and in the supercritical fluid. The positions of the critical points of these transitions were estimated. An interpretation of the observed phenomena is given: It leads to the new approach to the nature of the critical point of liquid-gas transition in mercury. It is shown also that the fourth derivative of the thermodynamic potential of mercury has a special feature in the metal-nonmetal transition region.