Factors influencing the mode of thermal decomposition of zirconium sulphate tetrahydrate

Abstract

The thermal decomposition process of zirconium sulphate tetrahydrate has been studied. Dehydration, which takes place via a crystalline monohydrate phase, is accompanied by the loss of small amounts of sulphuric acid apparently resulting from internal hydrolysis of the compound. This process gives a non-stoicheiometric zirconium sulphate which may exist in several modifications depending on the vapour pressure of the sulphuric acid around the sample during dehydration. The vapour pressure of the sulphuric acid is in turn controlled by such factors as the particle size of the tetrahydrate preparation, the size of sample, and the temperature and technique used during heating. Equilibration experiments have shown that a-Zr(SO4)2 is the stable anhydrous form. The X-ray powder diffraction patterns of a- and γ- Zr(SO4)2 have been indexed. Above 650� all forms of Zr(SO4)2 decompose to cubic ZrO2 which transforms to monoclinic ZrO2 at 800�.