Phase diagram of salt-water system determined by TG-DTA

Thermogravimetry (TG) and differential thermal analysis (DTA) techniques we re used to determine the solid-solution equilibrium curve between certain i norganic salts and water. The rate of evaporation of water through a pin ho le of an aluminum pan, containing a small amount of aqueous solution of the salt, was measured by TG and DTA. A slight change in the rate was found to occur when the solution crosses the solubility curve. The composition and temperature at which the vaporization rate changed were determined by diffe rentiating the TG curve with respect to time and then comparing with the li terature value. The solubilities of NaCl, KCl, and Na2SO4 crystals into wat er were determined rapidly with the accuracy of +/-1% for a small amount of sample solution. (C) 1999 Elsevier Science B.V. All rights reserved.