Effect of Al2O3 on phase separation and microstructure of R2O-B2O3-Al2O3-SiO2 glass system (R = Li, Na)

Abstract The investigation of selected properties in non-porous and porous R2O-B2O3-Al2O3-SiO2 (R = Li, Na) glasses indicates different effects of Al2O3 on phase separation and microstructure. Decrease of [BO4]− units in Na2O-B2O3-SiO2 glass system reveals a constant inhibition of phase separation with addition of Al2O3. In Li2O-B2O3-SiO2 glass system, the addition of Al2O3 leads to a non-linear behaviour. XRD pattern and MAS-NMR studies display a microstructure-dependence on partial crystallization and phase separation. An addition of up to 4 mol.-% Al2O3 changes the microstructure from isolated into bimodal and monomodal interconnected phases. Based on the analysed properties a simplified model is set up which explains the influence of Al2O3 on phase separation, crystallization and microstructure in Li2O-B2O3-Al2O3-SiO2 glasses.