The standard enthalpy of formation of anhydrous, monohydrated, and dihydrated zirconium bis(monohydrogenphosphate)

The enthalpies of solution of amorphous and crystalline Zr(HPO4)2.H2O, of Zr(HPO4)2, and Zr(HPO4)2.2H2O have been measured calorimetrically and the standard enthalpies of formation derived. The results are presented. In order to establish an unambiguous assessment of the degree of crystallinity of these exchangers, the ΔH0 of other Zr(HPO4)2.H2O samples prepared by different techniques with various conditions have also been determined. (author)