The influence of vapour pressure on the formation of anhydrous zirconium sulphates

Abstract

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.