Infrared and Mِssbauer studies of iron in aluminosilicate glasses

Samples of 10Fe2O3·10Al2O3·80SiO2 composition were prepared by the sol–gel method and heat-treated between 120 and 1300 °C under oxidising (air) conditions. These samples were studied by Fourier transformer infrared (FTIR) and Mössbauer spectroscopy. The results indicate that Fe3+ is in octahedral sites at 250 °C and in tetrahedral sites between 500 and 1300 °C. Goethite and hematite particles are present in the 250 and 500 °C samples and hematite particles in the samples heat-treated between 1000 and 1300 °C. The hematite particles, present in the samples, show a lower hyperfine field (47.91±0.08 T) than that usually seen for hematite (51.5 T). This is due to the fact of Al3+ ions take the place of Fe3+ ions in hematite particles.