Phase transformations in liquids and the liquid—gas transition in fluids at supercritical pressures
Institute for High Pressure Physics, Russian Academy of Sciences, Troitsk, Moscow, Russian Federation
It is an experimental fact that in the neighborhood of melting curves, including those measured at above-critical pressures and temperatures, all fluids have some short- and intermediate-range order and their excitation spectra contain high-frequency shear waves. At high pressure both smooth and sharp first-order phase transformations involving changes in liquid structure and properties can occur between various liquid states. However, at sufficiently high temperatures any liquid loses its identity and turns into an unstructured dense gas in which only longitudinal waves can propagate. This paper discusses theoretical and experimental evidence for the existence of a boundary between a 'solid-like' melt and a dense gas at supercritical pressures.