Properties and Structures of MgO–CaO–Al 2 O 3 –SiO 2 Glasses: Effects of Low‐Iron Oxide and Redox

ABSTRACT A series of mixed alkaline aluminosilicate glasses with low iron concentrations (0.04–0.64 wt% Fe 2 O 3 ) was studied, covering a wide range of properties, including melt viscosity, liquidus temperature, simulated Rosseland mean radiative absorption/conduction, fiber tensile strength, water contact angle, and surface tension. To elucidate the local environments of ferric and ferrous ions in the glass network, multiple spectroscopic techniques (UV–vis–near infrared (NIR), fourier transform infrared (FTIR), and Raman spectroscopy) and molecular dynamics (MD) simulations were used. The UV–vis–NIR study revealed that FeO in glass is directly proportional to the Fe 2 O 3 content, whereas FeO/total Fe 2 O 3 ratio was reduced slightly for single Fe 2 O 3 ‐doped glasses. The study revealed that the Rosseland radiative conduction coefficient, proportional to the reciprocal of the Rosseland mean absorption coefficient, and viscosity decreased with increasing Fe 2 O 3 (or FeO) content, whereas liquidus temperatures remained constant. The tensile strength of glass fibers with higher Fe 2 O 3 (or FeO) increased slightly, and the surface energy ratio of low‐iron to high‐iron glass decreased accordingly, which may be attributed to a decrease in hydroxyl content in the glasses with higher Fe 2 O 3 (or FeO) under the same melting conditions. With increasing Fe 2 O 3 content, both Q 4 and Q 2 units decreased, while Q 3 species increased. The findings for Q 4 and Q 3 are generally consistent with the results of the Raman spectroscopic study. MD simulations revealed that ferric ions (Fe 3+ ) in glass are primarily 4‐fold coordinated, forming Si–O–Fe bonds within the glass‐forming network. In contrast, ferrous ions (Fe 2+ ) exhibit 5‐ and 6‐fold coordination, acting as network modifiers. Cluster formation with Fe 3+ –O–Fe 3+ and Fe 2+ –O–Fe 2+ linkages was suggested only at higher Fe 2 O 3 levels in MD simulations and is consistent with the narrowing of the Fe 2+ –O absorption band at 1050 nm from UV–vis–NIR spectral analysis.