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

A modified reverse micelle process has been developed for the synthesis of nanospherical amorphous zircon precursor powders. It has been found that th e hydrolysis of a mixture of zirconium and silicon alkoxides within the wat er phase of a microemulsion can produce amorphous, nanospherical particles with a stoichiometric ZrSiO4 composition. Microemulsions were obtained by u sing cyclohexane as the oil phase, ammonium solutions as the aqueous phase, and Igepal Co520 as surfactant. Precise control of the stoichiometry of th e powders was achieved after the starting silicon and zirconium alkoxides w ere appropriately modified. In particular, silicon alkoxide was pre-hydroly zed under acidic conditions while zirconium alkoxide was reacted with chela ting agents. The as-prepared powders consisted of amorphous nanospherical p articles with compositional homogeneity. Heating of powders led first to in cipient tetragonal zirconia crystallization at a temperature of 900 degrees C. The onset of crystalline zircon formation was detected at 1200 degreesC, while the conversion was complete after heating the amorphous precursor po wders at 1300 degreesC for 2 hours.