Synthesis and characterization of α-hopeite, Zn3(PO4)2·4H2O

Orthorhombic α-Zn3(PO4)2·4H2O, α-hopeite, was synthesized from an aqueous solution of zinc acetate and orthophosphoric acid. The synthesis from these starting materials yielded best results with respect to purity and crystallinity. Structural characteristics of the compound were investigated by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), and thermogravimetric/differential thermal analysis (TG/DTA). Supplemental data came from surface area, particle size distribution, and density measurements. The obtained compound proved to be highly crystalline and stoichiometric. Dehydration of α-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 coating process. The dehydration behavior can be explained by results from low-temperature diffuse reflectance IR spectroscopy (DRIFT).