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 xAl ₂O ₃-(100 − x)SiO ₂ (x = 0, 10, 20 and 30 mol) systems by differential scanning calorimetry, X-ray diffraction, infrared (IR) spectroscopy and transmission electron microscopy. The SiO ₂-Al ₂O ₃ gels exhibit lower G-G transition temperature than the pure SiO ₂ reference gel. Adding Al ₂O ₃ to the SiO ₂ gel can suppress the dependence of glass transition temperature (T _g) 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 Al ₂O ₃ content. This behavior is similar to that of the melt-quenched alumina-silica glasses.