Energetics of phosphate frameworks containing zinc and cobalt: NaZnPO4, NaH(ZnPO4)(2), NaZnPO4 center dot H2O, NaZnPO4 center dot 4/3H(2)O, and NaCoxZn1-xPO4 center dot 4/3H(2)O

摘要

Differential scanning calorimetry and high temperature oxide melt solution calorimetry were used to study the enthalpy of the alpha-beta phase transformation of NaZnPO4 and enthalpies of formation of alpha-NaZnPO4, NaH(ZnPO4)(2), NaZnPO4 center dot H2O, and NaCoxZn1-xPO4 center dot 4/3H(2)O (x = 0, 0.1, 0.2, 0.3). The enthalpies of formation from the oxides of cobalt substituted in NaZnPO4 center dot 4/3H(2)O do not depend on cobalt content, confirming similar acid-base interactions for Zn-PO4 and CO-PO4. While water molecules stabilize zinc phosphate frameworks through solvating a cation or forming extra hydrogen bonds, the partial substitution of water for sodium oxide to form NaH(ZnPO4)(2) represents the formation of an acidic compound with weaker acid-base interactions and less exothermic enthalpy of formation from oxides than Na-2(ZnPO4)(2). (c) 2007 Elsevier Inc. All rights reserved.