Structure and redox ratio of soda‐lime‐silica glasses with high iron oxide concentrations

Abstract The high temperature synthesis of glasses in the system (100‐x)(0.16Na ₂ O/0.10CaO/0.74SiO ₂ )/xFe ₂ O ₃ , x = 5 ÷ 20 mol% is reported. For Fe ₂ O ₃ concentrations ≤15 mol%, glasses are formed while the sample with 20 mol% crystallizes during cooling the melt. X‐ray diffraction shows the crystallization of magnetite. The microstructure of the glass‐crystalline sample is investigated by optical microscopy and scanning electron microscopy and two types of iron‐rich crystals corresponding to magnetite and hematite are detected. The refractive indices as determined by the Becke line method are in the 1.567 ‐ 1.639 range and. increase with increasing Fe ₂ O ₃ concentration. The structure is characterized using Infra‐red spectroscopy. The presence of symmetric stretching, asymmetric stretching and bending vibrations of Si‐O‐Si is detected and attributed to the occurrence of SiO ₄ tetrahedral units with varying numbers of nonbridging oxygens. Also, the increasing Fe ₂ O ₃ concentration results in occurrence of Fe‐O‐Si bonds indicating the glass network depolymerization due to Fe ₂ O ₃ addition. In all samples, the presence of Fe ³⁺ and Fe ²⁺ and the existence of iron ions in tetrahedral and octahedral coordination, as well as a very small amount of Fe ⁰ and the precipitation of hematite and magnetite in the glass‐crystalline sample is revealed by Mössbauer spectroscopy.