Structure modifications during thermal processing of silicon alkoxyde derived silica-iron oxide nanocomposites

Abstract

The effects of iron concentration in the matrix structure of monolithic γ-Fe₂O₃/SiO₂ nanocomposites with different thermal processing have been studied by means of X-ray diffraction, Fourier transform infrared spectroscopy, temperature programmed decomposition-mass spectrometry and thermogravimetric analysis. The chemical changes occurring during the formation and subsequent growth of iron oxide nanoparticles, have been found to modify the formation process of alkoxysilane derived xerogels as a consequence of the competition for water molecules in the reaction medium. Specifically, the water releasing from the xerogels is shifted towards higher temperatures as a consequence of Fe³⁺ aquocomplexes formed in early stages of the synthesis. The iron content is also associated with changes in the polycondensation of the silica matrix and in the performance of chemical additives used to preserve the mechanical properties of the studied nanocomposites. These modifications extend to the thermal processing of samples, hindering the decomposition and subsequent removal of residues.