HOMOGENEOUS PRECIPITATION OF MULLITE PRECURSORS

The synthesis of mullite powders or gels from an aqueous precursor sol ution has been studied. The starting solution is made by hydrolyzing T EOS into an aqueous solution of aluminium nitrate. When this solution is sprayed into a solution of ammonia in isopropanol, a nearly monopha sic mullite precursor is obtained, whereas if this precipitation is ma de into an aqueous solution of ammonia, or ammonium carbonate, a dipha sic colloidal precipitate is formed. By a slow and homogeneous precipi tation in aqueous solution, induced by in-situ generation of ammonia b y thermal hydrolysis of urea, a monophasic gel is also obtained. The s amples have been studied by DTA, DSC, TGA, XRD and dilatometry.