Supercritical phase separation in water-nitrogen mixtures

Abstract

The authors report phase separation of supercritical mixtures of H{sub 2}O and N{sub 2} at pressures to 2.1 GPa and temperatures to 830 K on the 75 mol% water isopleth. The compositions is fixed by loading a diamond anvil cell with a known mixture at temperatures above 400 C and pressures above 150 MPa. They measure the pressure using the pressure dependence of the Sm{sup 3+}:YAG fluorescence line at 6,178 {angstrom}. The shape of the coexistence curve for this isopleth implies a critical curve with a relatively weak dependence of the phase separation pressure on the temperature.