γ–Fe2O3/SiO2 and Fe/SiO2 nanocomposites, with a Fe/Si molar ratio of 0.25, were prepared by the sol-gel method starting from ethanolic solutions of tetraethoxysilane and iron (III) nitrate. After gelation the xerogels were oxidated or reduced. Samples were investigated by transmission electron microscopy, x-ray diffraction, differential scanning calorimetry, and thermogravimetry. Magnetic properties of the samples were investigated at room temperature (RT) and at 77 K. Nanometric particles supported in the silica matrix were obtained in all cases. Bigger particles (10 nm) were obtained in the case of Fe/SiO2 nanocomposites with respect to the γ–Fe2O3/SiO2 samples (5–8 nm). A slight effect of sol dilution on particle size was observed only in the case of γ–Fe2O3/SiO2 nanocomposites. A superparamagnetic behavior was shown at RT only by γ–Fe2O3/SiO2 nanocomposites. Iron-based composites exhibited coercivity values higher than 700 Oe at RT.
Dynamic Mechanical Relaxation of Poly(2‐Hydroxyethyl Acrylate)‐silica Nanocomposites Obtained by the Sol‐gel Method
