SYNTHESIS AND CHARACTERIZATION OF o-HOPEITE, Zn_3(PO_4)_24H_2O

摘要

Ortborbombic a-Zn_3(PO_4)_2.4H_2O, a-bOPeile, was synthesized from an aque- ous solution of zinc acetate and orthophosphoric acid. The synthesis from these starting materials yielded best results with respect to purity and crys- tallinity. Structural characteristics of the compound were investigated by X-ray diffraction (XRD), Fourier transform infrared (Fr-IR), scanning elec- tron microscopy (SEM), and thermogravimetric/differential thermal analysis (TG/DTA). Supplemental data came from surface area, particle size distribu- tion, and density measurements. The obtained compound proved to be highly crystalline and stoichiometric. Dehydration of a-hopeite is accompanied by at least two endothermic effects and already starts at temperatures <373 K. This observation has important implications for the technical zinc phosphate coat- ing process. The dehydration behavior can be explained by results from low-temperature diffuse reflectance IR spectroscopy (DRIFT).