Chemical durability of the iron-containing sodium borosilicate glasses

• Iron-containing porous glasses were obtained from Na 2 O-B 2 O 3 -SiO 2 -Fe 2 O 3 system. • The Fe 3+ ions’ coordination affected chemical durability of Na 2 O-B 2 O 3 -SiO 2 glasses. • Porous glass formation ability depended on Na 2 O/B 2 O 3 molar ratio. • Leaching behavior and Yun-Bray-Dell model for Na 2 O-B 2 O 3 -SiO 2 glasses correlated. • Criterion for obtaining a magnetite-containing porous glass was proposed. The chemical durability of the phase-separated glasses in Na 2 O-B 2 O 3 -SiO 2 -Fe 2 O 3 system (with a constant content of SiO 2 - 70 mol %; 5, 6 and 8 mol % Na 2 O and 2-10 mol % Fe 2 O 3 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% Na 2 O in the entire studied range of Fe 2 O 3 content, as well as glasses with 8 mol % Na 2 O and Fe 2 O 3 content up to 4 mol % led to through-leaching with the production of porous glasses (PGs) in the form of plates. The coordination of Fe 3+ 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 = [Na 2 O]/[B 2 O 3 ]<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.