Range of solid solutions of silica in spinel type phase

Al2O3 - SiO2 mixed gel of varying compositions has been synthesised by using aluminium nitrate nonahydrate (AR) and tetraethyl orthosilicate (BDH) by coprecipitation technique. Phase evolution studies of these gels have been made by X-ray diffraction technique and Si-29 MAS NMR analysis. The lattice parameter of intermediate Al - Si spinel phase has been measured. The calculated data indicate that the composition of spinel phase does not alter irrespective of the composition of mixed gels chosen. Results demonstrate that slightly <28 wt-% SiO2 is likely to be present as solid solution with gamma-Al2O3 in Al - Si spinel structure. Mullitisation reactions of mixed gels of compositions on two sides of mullite stoichiometry are described.