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

The synthesis of zircon powders from an aqueous precusor sol has been studi ed. The starting solution, prepared by hydrolyzing TEOS in an aqueous solut ion of zirconyl nitrate, was refluxed then precipitated into an ammonia sol ution. The evolution of the precursor sol with reflux time and that of the precursor powder, i.e. the precipitate dried and ground, with heat treatmen t has been followed by several characterization techniques, viz. Raman spec troscopy, Si-29 MAS NMR spectroscopy, X-ray diffraction and DTA-TGA analysi s. It was found that zircon formation begins at 100 degrees C in the reflux ing precursor sol and is carried on into the precursor powder by reaction b etween amorphous silica and tetragonal zirconia, formed earlier during the heat treatment at temperatures above 1000 degrees C. A procedure for the pr eparation of zircon powders consisting of dense spherical particles based o n spray-drying of the precipitate, washed and re-dispersed in water after s ynthesis, is also described.