Kinetics of the isothermal crystallization of tetragonal modification of leucite and hexagonal modification of kalsilite from differently prepared precipitated amorphous aluminosilicate precursors were investigated at three different temperatures. Kinetic analyses of the transformation processes have shown that the crystallization of leucite occurs the same way as the crystallization of kalsilite and follows a pseudo-zero-rate kinetic equation. The apparent activation energies calculated by the Arrhenius equation were 373 kJ/mol for the crystallization of kalsilite and 403 kJ/mol for the crystallization of leucite, which is explained by the different microstructures of the prepared precursors.

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Abstract. A novel method for preparation of Fe2+ /Fe 3+ 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 57 Fe Mössbauer 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. Mössbauer measurements revealed the presence of both Fe 2+ and Fe 3+ states providing a chance for perspective catalytic application of the obtained Fe-mullite.