DIFFERENTIAL THERMAL-ANALYSIS OF THE LIQUIDUS RELATIONS IN THE SYSTEM NACL-H2O TO 6 KBAR

The liquidus relations in the system NaCl-H2O were investigated between 300 and 925-degrees-C and between 0.4 and 6 kbar for compositions between 27.6 and 100 mol% NaCl by high-pressure differential thermal analysis. The PT slope of the liquidus increases from 10.5-degrees-C/kbar for a composition with 27.6 mol% NaCl to 20.8-degrees-C/kbar with 90 mol% NaCl to 21.8-degrees-C/kbar with pure NaCl. The PT slope of the vapor saturation surface at the composition with 27.6 mol% NaCl is linear over the pressure range investigated and has a slope of 294-degrees-C/kbar. On the basis of the experiments the composition of the liquids along the NaCl-rich part of the three-phase assemblage halite + liquid + vapor was determined: the liquid composition varies nearly linearly to within +/- 0.5 wt% NaCl at temperatures above 480-degrees-C, following the expression wt% (NaCl) = 0.1412T (degrees-C) - 12.96.