Abstract
Nanosized iron oxide powder with an average crystallite size of 35, 100 and 150 nm was prepared by thermal evaporation and coprecipitation techniques. The synthesised powders were characterised by X-ray diffraction analysis technique, reflected light microscope, TEM and scanning electron microscope. The powder was pressed into compacts which then isothermally reduced in hydrogen atmosphere at 400-600°C. The reduction course was followed up by means of weight loss technique. The effect of crystal size and reduction temperature on the reduction behaviour of nanosized iron oxides compacts was investigated. The values of apparent activation energy calculated from the experimental results together with the application of gas solid reaction model were used to elucidate the reduction mechanism of iron oxide in nanoscale. It was observed that both the reduction temperature and crystal size of the compact greatly affect the reduction mechanism of iron oxide. It can be reported that the complete reduction process of nanosized iron oxides can be performed at relatively low temperatures (450-600°C). At the initial stages of reduction, the reduction rate is controlled by combined effect of gas diffusion and interfacial chemical reaction mechanism for all nanosized compacts whereas the controlled mechanism was varied at the final stages of reduction according to the crystal size of iron oxides.