NOVEL GAMMA-FE2O3 SIO2 MAGNETIC NANOCOMPOSITES VIA SOL-GEL MATRIX-MEDIATED SYNTHESIS/

Magnetic single-domain gamma-Fe2O3 nanoclusters have been prepared by (i) coprecipitation of ferrous and ferric salts encapsulated within so l-gel derived silica (SiO2), and (ii) oxidation of ferrous cations inc orporated in a sulfonated, ion-exchange porous silica matrix. In the f irst method, a SiO2 coating was formed on the Fe2O3 nanoclusters by hy drolysis and condensation of tetraethoxysilane. In the second route, s ulfite (SO3-) functionalized silica was synthesized from a modified so l-gel precursor resulting in a porous gel with a narrow pore size dist ribution. The SiO2 coating and sulfonated SiO2 matrix provide the mean s for homogeneous dispersion of Fe2O3 clusters. The SiO2-coated Fe2O3 nanoclusters are spherical with 4-5 nm diameters. Acicular crystalline Fe2O3 nanoclusters with diameters of similar to 4 nm and lengths of 1 0-20 nm were found in the porous sulfonated gel matrix Magnetization a nd Mossbauer studies indicated that the gamma-Fe2O3/SiO2 nanocomposite s are superparamagnetic. The magnetic properties can be manipulated vi a the matrix structure and synthesis conditions. (C) 1997 Acta Metallu rgica Inc.