Precipitation of γ-Fe₂O₃ from Ultrahigh Temperature Plasma

Precipitation of ultrafine iron oxides from an argon inductively coupled plasma of ultrahigh temperature (ICP) has been investigated. Aqueous solutions of iron salts and solid α-Fe₂O₃ are introduced into ICP. The iron oxides are precipitated in two types of collectors, a water-cooled tube with an open end (collector A) and a tube with a closed end (collector B). The iron oxides are γ-Fe₂O₃, regardless of the mother reactants and the type of the collectors. However, particle morphology ofγ-Fe₂O₃, is found to be largely dependent upon the collectors. The particles in the collector (A) are ultrafine (≃10 nm in size) and show no clear habit, owing to rapid quenching. In the collector (B), however, relatively large bi-crystals and polyhedra (10–70 nm) are formed, apparently through the coalescence growth enhanced by the convectional gas flow in the collector.