SYNTHESIS AND CHARACTERIZATION OF SOME IRON-OXIDES BY SOL-GEL METHOD

Several iron oxides and mixtures of iron oxides have been prepared by heating the product of a sol-gel reaction between iron(III) nitrate an d ethylene glycol in different atmospheres and at different temperatur es. The materials were characterized by Mossbauer spectroscopy, powder X-ray diffraction, and transmission electron microscopy. Ferrous iron was found to be present in an appreciable amount in the products of t he sol-gel reaction, but its origin is not yet understood. Heating at 300-degrees-C in N2 atmosphere, cooling in air to ambient temperature, and heating again at 300-degrees-C in static air produced single-phas e maghemite with a mean crystallite diameter (MCD) of 18 nm. Well crys tallized hematite (MCD = 110 nm) was obtained at 300-degrees-C in O2 a tmosphere. Mixtures of poorly crystallized maghemite and magnetite wer e observed to exhibit room-temperature Mossbauer spectra which closely resemble those reported for sodium-modified maghemite. A mixture of m agnetite, wustite, and metallic iron was obtained by heating at 800-de grees-C in N2 atmosphere. (C) 1994 Academic Press, Inc.