Clarifying the gel-to-glass transformation in Al2O3-SiO2 systems

In this paper, we clarify the gel-to-glass (G-G) transformation behavior of the sol-gel derived xAl2O3-(100 − x)SiO2 (x = 0, 10, 20 and 30 mol) systems by differential scanning calorimetry, X-ray diffraction, infrared (IR) spectroscopy and transmission electron microscopy. The SiO2-Al2O3 gels exhibit lower G-G transition temperature than the pure SiO2 reference gel. Adding Al2O3 to the SiO2 gel can suppress the dependence of glass transition temperature (Tg) on hydroxyl concentration, and this effect is attributed to the highly cross-linked structure in alumina-silica gels. In addition, the Al-rich phase separates from the Si-rich matrix phase, and such immiscibility increases with increasing Al2O3 content. This behavior is similar to that of the melt-quenched alumina-silica glasses.