New phase diagrams with anomalous region, supercritical solid-like state, liquid phase boundary, and dwij point

Abstract

A Gibbs free energy-based thermodynamic analysis for regular fluids reveals the extension of liquid-vapor (L-V) line, beyond the critical point, to a newly discovered “Dwij point” (DP). At DP, this line turns around and goes back to the melt-solid (S-L) boundary, which together with the S-L and L-V lines delimits the region of liquid/supercritical liquid-like (L/SCLL) state. Consequently, a thermodynamic “solid-like” state is identified, which exists between the L/SCLL and melt-solid lines. Moreover, beyond DP only two phases, gas and solid exist, with the transition occurring via supercritical gas-like and solid-like states. These findings, in conjunction with the anomalous region around the critical point lead to historic modifications to the phase diagram. Consequently, the new phase diagrams for nine fluids are presented. Although the extension of supercritical liquid-like/gas-like boundary for hydrogen is similar, variations do exist. These discoveries may reconcile the thermodynamic transitions and dynamic transitions, which occur beyond DP.