Higher Fe2+/total Fe ratio in iron doped phosphate glass melted by microwave heating

Iron doped phosphate glasses containing P2O5–MgO–ZnO–B2O3–Al2O3 were melted using conventional resistance heating and microwave heating in air and under reducing atmosphere. All the glasses were characterised by UV–Vis–NIR spectroscopy, Mössbauer spectroscopy, thermogravimetric analysis and wet colorimetry analysis. Mössbauer spectroscopy revealed presence of iron predominantly in the ferrous oxidation state on two different sites in all the glasses. The intensity of the ferrous absorption peaks in UV–Vis–NIR spectrum was found to be more in glasses prepared using microwave radiation compared to the glasses prepared in a resistance heating furnace. Thermogravimetric analysis showed increasing weight gain on heating under oxygen atmosphere for glass corroborating higher ratio of FeO/(FeO + Fe2O3) in glass melted by direct microwave heating. Wet chemical analysis also substantiated the finding of higher ratio Fe+2/ΣFe in microwave melted glasses. It was found that iron redox ratio was highest in the glasses prepared in a microwave furnace under reducing atmosphere.