The crystallization process and chemical durability of glass-ceramics based on the Li_2O-B_2O_3 (Fe_2O_3)-SiO_2 (GeO_2) system

摘要

The effect of partial replacements of GeO_2 for SiO_2 and Fe_2O_3 for B_2O_3 on the crystallization process of a Li_2O-B_2O_3-SiO_2 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 (T_g) and softing (T_s) 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.