The crystallization process and chemical durability of glass-ceramics based on the Li2O–B2O3 (Fe2O3)–SiO2 (GeO2) system

The effect of partial replacements of GeO2 for SiO2 and Fe2O3 for B2O3 on the crystallization process of a Li2O–B2O3–SiO2 glass-ceramic was followed by means of differential thermal analysis (DTA), X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The chemical resistance of the glass-ceramics toward the attack of acid media was also determined. Results showed a decrease in both transition (Tg) and softing (Ts) temperatures by the replacement processes. Varieties of crystalline phases including Ge–lithium disilicate ss, lithium diborate, lithium metasilicate as well as lithium iron silicate ss containing germanium were formed in the crystallized glasses. The crystallization of meta- and/or disilicate and their proportions depend on both temperature and duration of the process. The chemical durability of the crystallized glasses was improved by the replacement processes. The obtained durability data depend on the nature, concentration of the crystalline phases formed, the nature of glassy matrix, and the microstructure of the glass-ceramics. The role played by the glass oxide constituents in determining crystal phases, their solid solutions, microstructure, and the chemical durability of the glass-ceramics was discussed.