Determination of structural, thermodynamic and phase properties in the Na2S-H2O system for application in a chemical heat pump

摘要

Structural, thermodynamic and phase properties in the Na2S-H2O system for application in a chemical heat pump have been investigated using XRD, TG/DTA and melting point and vapour pressure determinations. Apart from the known crystalline phases Na2S.9H(2)O, Na2S.5H(2)O and Na2S a new phase Na2S.2H(2)O has been proven to exist. Na2S.1/2H(2)O is not a phase but a 3:1 mixture of Na2S and Na2S.2H(2)O, presumably stabilised by very slow dehydration kinetics. The vapour pressure-temperature equilibria of the sodium sulphide hydrates have been determined and a consistent set of thermodynamic functions for these compounds has been derived. XRD measurements indicate the topotactic character of the transitions between the hydration states. (C) 2002 Elsevier Science B.V. All rights reserved. [References: 23]