CaCl<sub>2</sub>-H<sub>2</sub>O in the supercritical and two-phase ranges

Abstract

Critical temperatures (Tc) and densities ρc for aqueous CaCl2 solutions were measured using two different optical techniques. Measurements of Tc were made using sealed silica capillaries containing 0.3, 0.5, 1.0 and 2.0 molal CaCl2(aq) solutions. Tc`s from these measurements are 661, 666, 678, and 738 K, respectively. Critical temperatures were also determined from measured homogenization temperatures and the observed mode of homogenization (i.e., to the liquid or vapor phase or by fading of the meniscus) in synthetic fluid inclusions. Critical temperatures determined by this method for 1.0, 2.0, and 3.0 molal CaCl2(aq) solutions are 680, 739, and 838 K, respectively. Tc for 4.0 molal CaCl2(aq) was found to be in excess of 933 K. Critical pressures (Pc}) could not be accurately determined from these measurements but were estimated from another source. Our data are in fair agreement with previously published data at and below 1.0 mol-∙kg-1}. Above 1 mol∙kg-1}, data from the two published sources of CaCl2(aq) show substantially different trends, with the data from this study agreeing with the more recent of the two reports. Estimated values of ρc are given for the solutions examined in the capillary tube experiments. These measurements are based on estimated tube volumes, measured liquid volumes, and solution densities at ambient temperature.