VOLUMETRIC PROPERTIES OF AQUEOUS SODIUM SULFATE SOLUTIONS AT HIGH TEMPERATURE AND PRESSURES.

The authors studied the volumetric properties of aqueous sodium sulfate solutions at temperatures 323-573 degree K, pressures 10-80 MPa, and concentrations 0. 05-0. 3 mole/kg of H//2O. The measurements were performed on a setup based on the method of study of volumetric properties using a constant volume piezometer. For the preparation of the solutions ultra-pure 6-4 grade sodium sulfate was used. The concentration of the solutions was determined gravimetrically. It is evident that the electrostriction effect of the electrolyte on the solvent increases with temperature and is decisive at high temperatures. This effect weakens as the pressure rises. A comparison of the calculated thermodynamic data with similar data for the system NaCl minus H//2O shows that the sodium sulfate solutions are characterized by lower values of the apparent volumes of the salt. This indicate a stronger electrostriction interaction in Na//2SO//4 solutions in comparison with the 1-1-valent electrolytes, this difference, typical for room temperatures at 0. 1013 MPa, being maintained up to fairly high temperatures and pressures (at least up to 573 degree K and 80 MPa).