Synthesis and characterization of gel-glasses in the SiO₂-ZrO₂-Al₂O₃ system

In the present work we report studies on the SiO₂-rich glass formation in ternary oxide system Al₂O₃- SiO₂-ZrO₂. Gels with composition 5%-90%-5% have been synthesized by the sol-gel method in acid media and then sintered at 1650°C for 2 and 10 hours. The phase composition of the as obtained materials was compared with the composition obtained by quenching of melts. The structure evolution of gels annealed at different temperatures up to 1650°C was followed by thermal analysis, X-ray diffraction. The powders consisted mainly of amorphous phase up to 1200°C where partial crystallization of cristobalite was observed. The presence of Zr and Al in the silica network at high temperatures was investigated. The crystallization of gels at high temperatures and the crystalline phases formed are related to the preparation conditions and the thermal treatment. For samples treated at 1650°C, zircon, silica and alumina were observed, while in the case of samples from quenched melts, zircon was the only crystalline phase detected.