Crystallization of gel-derived and quenched glasses in the ternary oxide Al2O3–ZrO2–SiO2 system

We studied glass formation in the SiO2-rich region of the ternary oxide system Al2O3–ZrO2–SiO2. Gels with the composition 5–5–90 mol% have been synthesized by the sol–gel method in acid media and then treated up to 1650 °C and kept for 2 and 10 h. A glass with the same composition has been obtained by quenching in water from the melt. The structural evolution of gels annealed at different temperatures up to 1650 °C was followed by thermal analysis, X-ray diffraction, specific surface area, density measurements and IR spectroscopy. The materials consisted mainly of amorphous phase up to 1200 °C, at which partial crystallization of cristobalite was observed. The presence of Zr and Al in the silica network at high temperatures was investigated by IR spectroscopy. The crystallization of gels at high temperatures and the crystalline phases formed are related to the preparation conditions and the thermal treatment. For samples from quenched melts zircon was the only crystalline phase detected, while in the case of the samples slowly cooled down from 1650 °C, zircon, silica, zirconia and alumina or mullite were observed depending on the treatment time.