Crystallization and microstructure in K2O substituted SiO2–MgO–Al2O3–Li2O–AlPO4 glass-ceramics

Abstract

The substitution of K+ ion by Ca2+ or Sr2+ in K2O–SiO2–MgO–Al2O3–B2O3–MgF2–Li2O–AlPO4 glass is executed and the relevant effects on crystallization and microstructure are explored. The glass monoliths obtained by single-step melt-quenching at 1500 ± 10 °C were transparent in nature. Density of base glass was evaluated as 2.66 ± 0.03 g cm−3 and found to be decreased by in presence of CaO or SrO. Opaque glass-ceramics were derived from the transparent glasses by controlled heat-treatment at 1000 ± 10 °C and the predominant crystalline phase was identified as fluorophlogopite mica, KMg3AlSi3O10F2 by X-ray diffraction. Field emission scanning electron microscopy revel that the plate like fluorophlogopite mica crystals predominated in base glass-ceramic (without CaO or SrO doped) but changed to nanocrystalline morphology containing droplet like spherical shaped mica crystallites (average size 200–400 nm) on addition of CaO and SrO. Highest density (=2.74 ± 0.03 g.cm-3) observed for SrO containing glass-ceramic is attributed to the nanocrystalline morphology.