We report the synthesis and characterization of iron-bearing sodium borosilicate glasses with an Fe₂O₃content lower than 10 mol%.

Glass containing chromium is a promising material for use in various modern fields of application (laser technology, optoelectronic devices, and luminescent resources). Chromium oxides are well-known nucleating agents that can cause crystallization. One of the most commonly observed crystalline phases in silicate glasses is cristobalite, which lowers their mechanical strength, leading to the destruction of the material. The objective of this investigation was to study in detail the crystallization of cristobalite in sodium borosilicate glass in the presence of 2 mol% Cr₂O₃, depending on the thermal history of the glass. The glass was studied using XRD, SEM, EPR, FTIR-spectroscopy, XPS, and solid-state NMR. Eskolaite, α-Cr₂O₃, which had crystallized in this glass, stimulated the bulk crystallization of cristobalite at 550 °C after isothermally treating it for 72 h, due to the phase-separated structure of the glass with its interpenetrating phase morphology. Polytypism, resulting in the incorporation of alkalis into the cristobalite structure, was observed. Cr₂O₃ causes the catalytic crystallization of cristobalite at an extremely low temperature, which is at lower concentrations and temperatures than in glass containing Fe₂O₃ with a similar composition. The crystal growth rate and the incubation time for the crystallization of cristobalite were roughly estimated.

Glasses of the 8Na₂O-(22-x)B₂O₃-70SiO₂-xFe₂O₃ system, where x varies from 0.3 to 10 mol %, have been studied by dilatometry, X-ray powder diffractometry (XRPD), and transmission electron microscopy (TEM). The glasses were heat treated at temperatures of 550, 650, and 700°C for 144, 10, and 2 h, respectively. When comparing the data of dilatometry and electron microscopy, we conclude that phase-separated glasses have a difference between the onset deformation temperature and the glass transition temperature of more than 100°C, while for single-phase glasses, the difference is less than 65°C. According to XRPD, it is shown that in the glasses containing from 4 to 8 mol % of Fe₂O₃, cristobalite is formed after exposure at 700°C for 2 hours, whose reversible α-β-transition is fixed in the subsequent dilatometry as a sharp jump in the thermal expansion in the temperature interval of 190–210°C. Starting from 3 mol % of Fe₂O₃, magnetite is formed in the glasses whose content increases with an increase in the content of iron oxide.

Porous glasses (PGs) obtained from sodium borosilicate (NBS) phase-separated glasses via leaching are promising inorganic membranes. Introducing Fe₂O₃ into NBS glasses imparts ferrimagnetic properties due to magnetite crystallization. Leaching of such glasses leads to the formation of magnetic PGs with interesting electro-surface characteristics. This work aimed to investigate the process of obtaining magnetite-containing PGs from NBS glasses depending on silica content, using XRPD and Raman spectroscopy, studying the PG membranes’ structural characteristics and their sorption properties with respect to methylene blue (MB). Obtained PGs were characterized by a polymodal distribution of mesopores and a small number of micropores with specific surface area values of 32–135 m²/g and an average mesopore diameter of 5–41 nm. The kinetic data were analyzed using pseudo-first-order, pseudo-second-order, and intra-particle diffusion equations. The equilibrium isotherms were fitted with Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich models. MB adsorption was found to be a complex process. The glass with the highest specific surface area demonstrated the maximum sorption capacity (10.5 mg/g). The pore size of PGs allowed them to be considered potential novel magnetic membranes for ultrafiltration.