Inorganic Oxide Gels and Gel-Monoliths: Their Crystallization Behavior
The significance of kinetics in the ordering process in metal oxide gels and gel-monoliths during densification is discussed. Cry stallinity of TiO2 gels after different thermal treatments were examined by x-ray diffraction and electron diffraction techniques. The sequence of phase transformation was noncrystalline gel anatase + rutile. Crystallinity of gel powders and gel-monoliths of two compositions in the Na2O-Ba2O3-SiO2 system were examined after thermal treatment at different temperatures above the Tg. Results indicate that the crystallization rates are controlled by the composition and the catalytic activity of Na+ ions associated with hydroxy1 ions in rupturing the Si-O-Si bonds. Porous gel-monoliths are transformed into transparent monocrystalline glass by appropriate heat treatment just above Tg.
KeywordsThermal Treatment Differential Thermal Analysis Crystallization Behavior Crystallization Rate Anatase Phase
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