Preparation and Spectroscopic Characterization of Iron Doped Mullite

A novel method for preparation of Fe2+/Fe3+ substituted mullite is described. Aluminosilicate gels are applied as precursors instead of crystalline aluminosilicates as used in other common syntheses. The process is composed of three stages. First, iron is introduced into a homogeneous aluminosilicate gel by ion exchange. The gel is converted to a mixture of mullite and amorphous silica in a 1263 K 3 h isothermal calcination in the the second stage. Finally, in order to obtain the nano-scale pure mullite phase the formed amorphous silica is removed by a dissolution in alkaline media. The components formed in various stages of the process are characterized by 57Fe Mossbauer and Fourier transform infra red spectroscopies, X-ray diffraction method and scanning electron microscopy. Spectroscopic and diffraction methods helped the identification of the mullite phase. Mossbauer measurements revealed the presence of both Fe2+ and Fe3+ states providing a chance for perspective catalytic application of the obtained Fe-mullite.