A Study of α-Zn₂P₂O₇ Hygroscopicity

We have studied water vapor absorption by the α-phase of zinc pyrophosphate, Zn₂P₂O₇, at 25°C. This compound has been found to be highly hygroscopic owing to the formation of a crystalline hydrate with the composition Zn₂P₂O₇∙5H₂O. Removal of its water of crystallization has been shown to occur in three steps, starting at 60°C and reaching completion at 400°C. The phase composition of the dehydration product depends on heat treatment temperature. Below 500°C, we observe considerable amorphization and predominant formation of γ-Zn₂P₂O₇, whereas phase-pure α-Zn₂P₂O₇ can be obtained as a result of annealing at temperatures above 600°C.