engleski

Thermal tranformations of amorphous aluminosilicate gels

The intention of this study is to find a novel method for preparation of aluminosilicate-based ceramic materials by thermal the treatment of amorphous aluminosilicates (zeolite precursors) as an alternative to conventional methods based on the thermal treatment of kaolin, feldspar, and other silicate, aluminosilicate and/or oxide mixtures. For this purpose, amorphous aluminosilicates in the systems: Me2O-Al2O3-SiO2-H2O (Me = Li, Na, K, Rb and Cs) were prepared in two different ways: 1. By mixing together Me-silicate solutions (prepared by the dissolution of fumed silica in MeOH solutions) and Me-aluminate solutions (prepared by the dissolution of aluminum wire in MeOH solutions) at room temperature, the separation of precipitated amorphous solid phase, washing and drying. 2. By the preparation of amorphous Na2O-Al2O3-SiO2-H2O as described above, and then the exchange of sodium ions from the prepared amorphous aluminosilicate with Li+, K+, Rb+ and Cs+ ions from appropriate solutions. To follow thermally-induced phase transformations, amorphous aluminosilicates prepared in both described ways were heated at specific transition temperatures (determined by differential scanning calorimetry). In order to study the mechanisms of transformation of two differently prepared Me2O-Al2O3-SiO2-H2O systems, all precursors (amorphous aluminosilicates) and crystalline phases obtained by their thermal treatment were characterized by X-ray powder diffraction, infrared spectroscopy, energy-dispersive-X-ray spectroscopy, scanning calorimetry and thermogravimetry, scanning electron microscopy and transmission electron microscopy. Structural and chemical properties of the obtained crystalline solids as well as the kinetics of their formation are discussed in the terms of the chemical compositions of the precursors and the methods of their preparation.

Thermal transformations; Amorphous aluminosilicate gels; Ceramics

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