Phase relations in the system NaCl-KCl-H 2O. Part I: Differential thermal analysis of the NaCl-KCl liquidas at 1 atmosphere and 500, 1000, 1500, and 2000 bars

Abstract

A simple differential thermal analysis (DTA) technique has been developed to study phase relations of various chemical systems at elevated pressures and temperatures. The DTA system has been calibrated against known melting temperatures in the system NaCl-KCl. Isobaric sections of the liquidus in the system NaCl-KCl have been determined at pressures of 1 atmosphere and 500, 1000, 1500, and 2000 bars. Using the least-squares method, the following equation was used to fit the experimental data: T(°C)= ∑ i=0 6 a iX i KCl where T is the liquidus temperature, X KCl is mole fraction of KCl, and a i (listed below) are the derived empirical constants. P (bars) a o a 1 a 2 a 3 a 4 a 5 a 6 1 atm. 800.1 −334.2 781.6 −6490.3 17553.1 −17638.4 6098.3 500 813.5 −354.9 743.3 −6011.7 16406.4 −16516.3 5702.8 1000 824.5 −406.7 1446.8 −8818.4 21253.5 −20343.7 6839.4 1500 838.6 −418.7 1434.7 −8819.0 21557.9 −20908.4 7123.1 2000 848.5 −381.5 1246.9 −8605.0 21785.8 −21449.1 7375.8 The liquidus temperatures estimated from these equations are within ±3°C of experimental values. The measured liquidus temperatures at 1 atmosphere agree with the best available data to within 5°C. The melting temperatures for pure end members at higher pressures agree with the values calculated from the Simon equation (Clark, 1959) to within 3°C. No previous melting data are available for the intermediate compositions at elevated pressures. Using the data in both heating and cooling scans, the minimum melting temperature at 1 atmosphere in the system was located at 658° ± 3° C where the sample has an equimolar composition.