Effect of temperature on reduction of nanocrystalline Fe 2 O 3 into metallic iron

Abstract

The synthesis of ultrafine magnetic material with large saturation magnetisation and high coercivity has received much attention, owing to its wide applications. The reduction of nanocrystalline Fe₂O₃ into metallic iron was studied. The iron oxide precursor was synthesised by thermal evaporation of iron acetate and then pressed into cylindrical shape compacts before being fired at 500°C for 1 h in a muffle furnace.

The prepared nanocrystalline Fe₂O₃ was characterised using X-ray diffraction analysis technique, reflected light microscope and scanning electron microscope. The reduction behaviour of nanocrystalline Fe₂O₃ in hydrogen atmosphere at 450–600°C has been studied using thermogravimetric techniques. The reduction rate is controlled initially by the interfacial chemical reaction mechanism, while the solid state diffusion is the rate controlling mechanism at final stages. The reduction temperature has a great effect on physicochemical properties of produced metallic iron during reduction of nanocrystalline Fe₂O₃. Metallic iron was formed in nanosized grains of 100–200 nm, while grain growth and highly coalescence were observed at reduction temperatures higher than at firing temperatures. Diluted magnetic nanoiron metal was formed with Hc ranged from 25 to 94 Oe, Br from 0·5 to 1·8 emu g⁻¹ and Bs from 24·5 to 41·4 emu g⁻¹.