An infrared study of crystallization in sodium-disilicate glasses containing iron oxides

The infrared absorption spectra of sodium-disilicate glasses containing various amounts of Fe₂O₃ ([Na₂O · 2 SiO₂]_1-x [Fe₂O₃]_x, where x = 0.05, 0.1 and 0.2) were investigated in the wavenumber range from 200-2000 cm^-1. The addition of Fe₂O₃ to the sodium-disilicate glass does not seem to introduce any new absorption band as compared with the spectrum of a pure sodium-disilicate glass; nevertheless, a general shift of the existing absorption bands toward lower wavenumbers is observed. The amount of shift is, in fact, proportional to the content of Fe₂O₃ in the glass. This observation is consistent with the recently proposed structural model for the bonding of Fe³⁺ ions in the iron-sodium-silicate glass system. Annealing of 20 mol% iron oxide glasses at 550 and 580°C produced an extra sharp infrared absorption peak at about 610 cm^-1 wavenumber. This new peak is believed to be related to the crystallized particles of the glass as concluded from both a scanning electron micrograph and an electron diffraction pattern.