Silica gels containing transition metal oxides

The sol–gel synthesis of silica gels containing transition metal oxides (Fe, Co, Ni) is of great interest for obtaining color glasses and films as well as materials with magnetic properties. In the present work, silica gels containing transition metal oxides have been synthesized over a wide concentration range (from 0.5 to 50 mol%). The resulting color gels have been treated in the temperature range from 100 to 1200 °C. the thermal treatment of gels the structural evolution and phase formation have been studied by means of IR Spectroscopy, X-ray diffraction analysis (XRD), transmission electron microscopy (TEM) and Mössbauer spectroscopy. By XRD, the size evolution of the α-iron oxide nanoparticles has been established after treatment at different temperatures. After decomposition of the iron salt at 200 °C, the resulting iron oxide consists only of superparamagnetic nanoparticles. The thermal treatment at higher temperatures leads to increased particle size, to formation of finely dispersed hematite and to a Mössbauer spectrum with a hyperfine magnetic structure. It is established by TEM and XRD analysis that synthesized materials possess uniformly distributed nanoparticles with sizes in the range from 10 to 50 nm.