Morphological changes accompanying gaseous reduction of SiO 2 doped wüstite compacts

Abstract

Pure wüstite was prepared from the gaseous reduction of reagent grade (99·5%) Fe₂O₃ at 1000°C, in 50CO–50CO₂ gas mixture. Compacts of 0·5% and 2%SiO₂ doped wüstite were made and annealed for 3 h at 1000°C in 50CO–50CO₂ gas mixture. These compacts were isothermally reduced in H₂, CO and 50H₂–50CO mixture at a temperature range 900–1050°C. The oxygen weight loss during reduction process was recorded as a function of time. X-ray diffraction (XRD), SEM and porosity measurements were used to characterise the annealed and reduced samples. The influences of temperature, gas composition and silica contents on the reduction behaviour and the morphology were investigated. It was observed that the addition of silica decreased the porosity owing to the formation of iron silicate phases. The reduction rate increases with temperature and in presence of hydrogen in the gas mixture while it decreases with increasing silica content owing to decreasing porosity of compacts. The apparent activation energy values were calculated and correlated with the gas–solid reaction formulations to elucidate the corresponding mechanism at both early and final reduction stages. The reduced iron was formed in different morphology including whiskers and platelets structures which are temperature and gas composition dependent.