INFLUENCE OF VAPOUR PRESSURE ON FORMATION OF ANGYDROUS ZIRCONIUM SULPHATES

The anhydrous products resulting from the dehydration of Zr(SO4)2,4H2O in external atmospheres of controlled H2SO4 and SO3 partial pressures consist of three polymorphs, two of which, γ- and β-Zr(SO4)2, are metastable and equilibrate to the stable phase, α-Zr(SO4)2. The rates of decomposition of these anhydrous sulphates to cubic ZrO2 have been measured and activation energies for the processes calculated. From these data the vapour pressure-temperature diagram for the anhydrous region of the ZrO2-SO3-H2O system has been delineated. This shows the existence range of γ-Zr-(SO4)2 lies within that of β-Zr(SO4)2 while both lie within that of the stable α-phase. The function of physical factors, such as particle and sample size and heating technique, in controlling phase formation during dehydration in air is interpreted in terms of the vapour pressure-temperature diagram. © 1969, CSIRO. All rights reserved.