Effect of liquid phase on the triple point pressure of argon

Abstract

We report here a systematic data analysis of the vapour pressure of argon at different amounts of the liquid phase to understand the thermodynamic behaviour of this inert gas around triple point. At the triple point plateau, the applied heat pulse melts a certain phase of solid argon into liquid and increases vapour pressure. It is observed that this vapour pressure attains the thermodynamic equilibrium pressure after a certain time interval. The expoential decay of the vapour pressure as a function of time at different fractions of the liquid phase shows two different features. In one region, the relexation time constant (τ) is low and is not varying with the liquid phase, while in the other region the value of τ increases with the amount of the liquid phase. Further, the peak pressure from the equilibrium pressure (ΔP_h), obtained from the fitting parameters, shows a dip at around 50% of the liquid phase. A qualitative physical interpretation has been given to explain these results.