Properties of zinc phosphates

Abstract

Hydrated Zn phosphates of compns. Zn3(PO4)2.4H2O, ZnHPO4.3H2O, ZnHP4.H2O, and Zn(H2PO4)2.2H2O were prepd. by crystn. from supersatd. solns. obtained by dissoln. of ZnO in H3PO4 of suitable concn. The isolated solid phases were identified chem., their phase compn. checked microscopically and by x-ray anal. The dhkl data obtained together with the corresponding intensities are listed. The course of thermal decompn. of the individual phosphates is described by DTA and thermogravimetric curves. In the decompn. of Zn3(PO4)2.4H2O, 2H2O are lost up to 150°, another H2O is liberated up to 200° and the resulting monohydrate is stable up to 25o°. The crystals of ZnHPO4.3H2O are dissolved in crystal H2O at 80°, 2H2O are lost up to 120° and the remaining H2O is lost up to 165°. At 200 to 230°, the substance is probably transformed to Zn2P2O7. The decompn. of ZnHPO4.H2O is similar to that of the trihydrate except the melting at 80° and the loss of 2H2O up to 165°. In the decompn. of Zn(H2PO4)2.-2H2O melting takes place at 70° and the 1st stage of dehydration probably corresponds to the formation of Zn h2P2O7 and the 2nd to that of Zn(PO3)2.