High-temperature dehydration of hydrophilic oxides ZrO₂ and Al₂O₃

The kinetics are studied and the mechanism is evaluated for dehydration of hydrophilic oxides ZrO₂ and Al₂O₃ that were prepared by isothermal decomposition of either zirconyl and aluminum nitrates or hydroxides. The hydroxides were prepared by freeze-drying of frozen cryogranules of colloidal solutions of zirconyl and aluminum hydroxonitrates. Nucleation is shown to be the rate-controlling stage of the dehydration of hydrophilic ZrO₂ prepared by thermolysis of zirconyl nitrate (the Avrami-Kolmogorov equation). Derivation of this equation is proposed to quantify the kinetic parameters of the process and to suggest reaction mechanisms on the basis of formal kinetic analysis of dα/dτ-f(α) relationships.