On the Theory of Fusion

TLDR

Fusion is unique in that a crystal cannot be overheated, distinguishing it from general phase equilibrium. The authors derived the exact equation of state for frozen argon, revealing a pressure–volume minimum that signals crystal breakdown and defines the melting point, and showed that crystalline helium requires positive pressure, though the theoretical predictions poorly match experiment.

Abstract

Although equilibrium between two phases is in general determined by both phases, fusion stands somewhat apart in that a crystal cannot be overheated. As a type of the simplest possible crystal, the exact equation of state of frozen argon has been developed here. It has been found that the pressure as function of the volume at a given temperature has a minimum, which means the breakdown of the crystal under these conditions. The temperature at which this minimum occurs at zero pressure is interpreted as the melting point. It has been found in accordance with experiment that a positive pressure is necessary for the existence of crystalline helium but the numerical agreement is bad.