Sol–gel synthesis via an aqueous semi-alkoxide route and characterization of zircon powders

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Abstract
The synthesis of zircon powders from an aqueous precusor sol has been studied. The starting solution, prepared by hydrolyzing TEOS in an aqueous solution of zirconyl nitrate, was refluxed then precipitated into an ammonia solution. The evolution of the precursor sol with reflux time and that of the precursor powder, i.e. the precipitate dried and ground, with heat treatment has been followed by several characterization techniques, viz. Raman spectroscopy, 29Si MAS NMR spectroscopy, X-ray diffraction and DTA–TGA analysis. It was found that zircon formation begins at 100°C in the refluxing precursor sol and is carried on into the precursor powder by reaction between amorphous silica and tetragonal zirconia, formed earlier during the heat treatment at temperatures above 1000°C. A procedure for the preparation of zircon powders consisting of dense spherical particles based on spray-drying of the precipitate, washed and re-dispersed in water after synthesis, is also described.

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