Phase transformations of mesoporous zirconia

The kinetics of the lamellar→hexagonal→cubic transformations of mesoporous zirconia prepared by using a neutral organic amine as the amphiphile have been studied in phosphoric acid medium. The lamellar→hexagonal transformation is preceded by a loss of the template molecules and the hexagonal→cubic transformation proceeds only when the lamellar form has entirely transformed to the hexagonal phase. The kinetics of the thermal transformation of lamellar zirconia to the hexagonal form have also been examined; this transformation also occurs and is accompanied by a loss of template molecules. Accordingly, the activation energy of the transformation is comparable to the hydrogen bond energy between the amine and the oxo-zirconium species. The phase transformations of mesoporous zirconia can be understood in terms of minimum energy surfaces.