The effect of surface tension on liquid-gas equilibria in isochoric systems and its application to fluid inclusions

We present a thermodynamic model to analyse the effect of surface tension on the size evolution and disappearance of a vapour bubble in an isochoric pure water system. The model relies on the minimisation of the Helmholtz energy of the system, derived from the IAPWS-95 formulation, and predicts the thermodynamic state, the vapour bubble radius, and the densities and pressures of the liquid and the vapour phase at a given temperature, volume, and mean density. The model reveals a transition from the stable to the metastable two-phase system, representing a bubble binodal, where both the liquid-vapour and the homogeneous liquid state can be stable. Furthermore, the transition from the metastable to the unstable two-phase system denotes the bubble spinodal, where the vapour bubble collapses from a non-zero radius upon homogenisation to the stable liquid state that extends to negative pressures. The model can be applied to the analysis of fluid inclusions in minerals of relevance for paleoclimatology, where the surface tension significantly influences the temperature of liquid-vapour homogenisation. It allows to calculate the formation density and the volume of a fluid inclusion from the observed homogenisation temperature and the measured bubble radius. (c) 2011 Published by Elsevier B.V.