Chemical durability of the iron-containing sodium borosilicate glasses

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 degrees C) in 3M aqueous HCl solution at boiling was studied. The structure of these glasses was investigated by means of XRPD, Mossbauer 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.