Structure modifications during thermal processing of silicon alkoxyde derived silica-iron oxide nanocomposites
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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.
KeywordsXerogels Nanocomposites Maghemite Thermal processing
The authors are gratefully thanked to M. P. Yeste and J. M. Gatica from the Catalysis & Chemistry of Solids group at the University of Cádiz for FTIR and TPD-MS measurements. D. Ortega expresses his thanks to the program for specialization of researchers from the UPV/EHU Office of the Vice-Chancellor for Research. Authors also would like to acknowledge the Spanish MCyT for financial support under project MAT2002-02179.
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