Sol-gel formation of γ-Fe2O3/SiO2 nanocomposites

Fe2O3-SiO2 nanocomposites with Fe/Si molar concentrations ranging between 0.25 and 0.57 were prepared by the sol-gel route. Tetraethoxysilane and iron(III) nitrate solution in ethanol were mixed and the hydrolysis reaction was promoted by the hydration water of the salt. The sols were gelated in air and then treated at 400 degreesC for 4 h. The effect of the gelation process on the formation of the final nanocomposites has been investigated by studing different factors, such as temperature and surface of evaporation/volume ratio of the sot. Nanoparticles of gamma and/or alpha iron oxide phase of different size were obtained in the silica matrix depending on the gelation conditions and on the later heat treatments. gamma -Fe2O3-SiO2 nanocomposites were obtained only when organic material was present into the pores of the gel silica matrix supporting their formation through a magnetite phase. At temperatures >400 degreesC, the y-phase begins to transform to the alpha -phase. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.