Zinc hydroxide sulphate and its transformation to crystalline zinc oxide

Abstract

The thermal transformation of zinc hydroxide sulphate hydrate to zinc oxide has been examined using synchrotron X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, and surface area measurements. By collecting X-ray diffraction data in situ, we found that the dehydration of zinc hydroxide sulphate pentahydrate proceeded in discrete steps to form anhydrous zinc hydroxide sulphate. This compound then decomposed to a mixture of zinc oxide and a compound tentatively identified as Zn₃(OH)₂(SO₄)₂ at ∼235 °C. At ∼360 °C, the final dehydroxylation occurred with the formation of zinc oxy-sulphate, Zn₃O(SO₄)₂, which then decomposed to ZnO at about ∼800 °C. Interruption of the dehydration process can be used to synthesize the intermediate compounds.