Chemical durability of the iron-containing sodium borosilicate glasses

Abstract

The chemical durability of the phase-separated glasses in Na2O-B2O3-SiO2-Fe2O3 system (with a constant content of SiO2 - 70 mol %; 5, 6 and 8 mol % Na2O and 2-10 mol % Fe2O3 heat treated at 550 °C) in 3M aqueous HCl solution at boiling was studied. The structure of these glasses was investigated by means of XRPD, Mössbauer and Infrared spectroscopy. Leaching of glasses containing 5 and 6 mol% Na2O in the entire studied range of Fe2O3 content, as well as glasses with 8 mol % Na2O and Fe2O3 content up to 4 mol % led to through-leaching with the production of porous glasses (PGs) in the form of plates. The coordination of Fe3+ cations affected the chemical durability. A correlation between leaching behavior and Yun-Bray-Dell (YBD) model for the chemical structure of sodium borosilicate glasses was observed. All of the glasses with interconnected phases morphology in the (1) YBD region (R = [Na2O]/[B2O3]<0.5) were suitable for through-leaching and obtaining PGs, while glasses in the (2) region were not. If the phase-separated glass composition falls into group (1) according to YBD model and the ferric ions are octahedrally coordinated, then a magnetite-containing PG can be obtained.