Fluid phases of argon: A debate on the absence of van der Waals’ “critical point”

Abstract

A phase diagram of argon based upon percolation transition loci determined from literature experimental p - V isotherms, and simulation values using a Lennard-Jones model shows three fluid phases. The liquid phase spans all temperatures, from a metastable amorphous ground state at 0K, to ultra-high T . There is a supercritical mesophase bounded by percolation transition loci, and a gas phase. Intersection of two percolation loci in the p - T plane thermodynamically defines a critical line between two coexisting gas and liquid critical states at T = T c , and the single mesophase for T > T c . A debate on the absence of a van der Waals critical point in the Gibbs p - T density surface is appended.