Sol-gel formation of gamma-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 wa s 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 proce ss on the formation of the final nanocomposites has been investigated by st uding different factors, such as temperature and surface of evaporation/vol ume 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 gelat ion conditions and on the later heat treatments. gamma -Fe2O3-SiO2 nanocomp osites were obtained only when organic material was present into the pores of the gel silica matrix supporting their formation through a magnetite pha se. At temperatures >400 degreesC, the y-phase begins to transform to the a lpha -phase. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Lt d. All rights reserved.