Thermal and calorimetric investigations on crystalline hydrates of barium hydroxide and their deuterated analogues

Abstract

The thermal decompositions of Ba(OH)2.8H20, Ba(OH)z.8D20, Ba(OH)2.H20 and Ba(OH)2. D20 were studied and the phase transitions were identified by DSC and DTA methods. The corresponding enthalpy changes were determined and compared with those calculated from the thermodynamic data. A decrease of the thermal stability was demonstrated for the deuterated crystal hydrates in comparison with the normal ones.The utilization of phase transitions in crystal hydrates as a kind of heat-energy storage explains the particular recent interest in this type of compounds. Specially, barium hydroxide and its crystal hydrates are of great interest both for the abovementioned purpose and for electronics applications.The thermal behaviour of Ba(OH) 2-8H20 has been studied by differential thermal analysis (DTA) [1][2][3][4][5], but the data obtained for the lower crystal hydrates and for the transition temperatures were contradictory. There are no corresponding data on Ba(OH)2-nD20.The object of the present work was to examine the thermal dissociations of Ba(OH)2.8H20 , Ba(OH)z. H20 , Ba(OH)2.8D20 and Ba(OH) z'D20 by two different methods, DTA and differential scanning calorimetry (DSC), in order to enrich the information available on the thermal behaviours of the above compounds and on the differences between normal and deuterated analogues, as well as to determine the enthalpy changes in the most important phase transitions.

The standard state thermodynamic properties for completely ionized hydrochloric acid and ionization of water up to 523 K

“…The temperature of 433.55 K is below the transition temperature 521 K [19,34], which indicated that perhaps the sample was a mixture of solids. However, the experimental enthalpies of solution for reaction (2), at temperatures of (333.55 and 368.15) K, are in excellent agreement with values calculated from ionic additivity using HCl(aq) [16], BaCl 2 (aq) [17] and auxiliary data for H 2 O(l) [18] and the (5)).…”