Preparation of nanospherical amorphous zircon powders by a microemulsion-mediated process

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Abstract
A modified reverse micelle process has been developed for the synthesis of nanospherical amorphous zircon precursor powders. It has been found that the hydrolysis of a mixture of zirconium and silicon alkoxides within the water phase of a microemulsion can produce amorphous, nanospherical particles with a stoichiometric ZrSiO4 composition. Microemulsions were obtained by using cyclohexane as the oil phase, ammonium solutions as the aqueous phase, and Igepal Co520 as surfactant. Precise control of the stoichiometry of the powders was achieved after the starting silicon and zirconium alkoxides were appropriately modified. In particular, silicon alkoxide was pre-hydrolyzed under acidic conditions while zirconium alkoxide was reacted with chelating agents. The as-prepared powders consisted of amorphous nanospherical particles with compositional homogeneity. Heating of powders led first to incipient tetragonal zirconia crystallization at a temperature of 900 °C. The onset of crystalline zircon formation was detected at 1200 °C, while the conversion was complete after heating the amorphous precursor powders at 1300 °C for 2 hours.

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