POLYTHERMAL STUDY OF PHASE EQUILIBRIA, SOLUBILITY AND CRITICAL PHENOMENA IN THE TERNARY SYSTEM CESIUM NITRATE – WATER – POLYETHYLENE GLYCOL-1500

Phase equilibria and solubility were studied by the visual-polythermal method in mixtures of components along ten sections of the composition triangle in the range of 10—110°C in the ternary system cesium nitrate – water – polyethylene glycol-1500. Using the method of volume ratio of liquid phases, the temperature of formation of the critical node of the monotectic state (78.8°C) and the dependence of the compositions of solutions corresponding to the critical solubility points of the separation region on temperature were found. The solubility of the components was determined and isothermal phase diagrams of the studied ternary system were constructed at 10.0, 25.0, 40.0, 50.0, 78.8, 90.0, and 100.0°C. It has been established that in the range of 10.0—40.0°C on isothermal diagrams there is a triangle of the cutonic state. Above the temperature of the onset of delamination (78.8°C), a monotectic triangle with adjacent fields of saturated solutions and delamination is realized on the isotherms. The distribution coefficient of polyethylene glycol-1500 between the equilibrium liquid phases of the monotectic state in the range of 78.8—100.0°C was calculated. It has been established that cesium nitrate is effective as a salting out agent for polyethylene glycol-1500 at temperatures above 90.0°C. At all temperatures in the study interval, polyethylene glycol-1500 significantly reduces the solubility of cesium nitrate in water.