Effect of Low Li₂O Content on Structure and Properties of R₂O-MgO-Al₂O₃-SiO₂ Glazes

A R₂O-MgO-Al₂O₃-SiO₂ (RMAS, R=Li, Na, K) glaze with low thermal expansion and low content of Li₂O was developed. The effects of Li₂O on structure and properties of the RMAS glaze were studied. The action mechanism of Li₂O was examined by using high temperature microscope, XRD, DTA, FE-SEM and AFM. With increasing content of Li₂O, fluidity of the RMAS glaze decreases first and then increases, while the crystal phase transforms from α-cordierite to α-cordierite and β-eucryptite solid solution (Li_xAl_xSi_3-xO₆). The coefficient of thermal expansion decreases from 3.79×10^-6 ℃^-1 (α_{L20-600 ℃}) to 1.22×10⁻⁶ ℃^-1 (α_{L20-600 ℃}), as the content of Li₂O is increased from 0 wt.% to 2.35 wt.%. When the content of Li₂O is 1.96 wt.%, the RMAS glaze possesses the highest comprehensive properties, with the highest α-cordierite content of 25.5 wt.% and coefficient of thermal expansion of 1.42×10^-6 ℃^-1 (α_{L20-600 ℃}). Compared with that of the sample without Li₂O, the activation energy values for the formation of α-cordierite in the RMAS glaze with 1.96 wt.% Li₂O decreased from 750.6 kJ·mol^-1 to 687.5 kJ·mol^-1.