Metallic iron whisker formation and growth during iron oxide reduction: basicity effect

Abstract

The effect of basicity on the metallic iron whisker growth during wüstite reduction was studied in the present investigation. Compacts of pure and CaO/SiO₂ doped wüstite were synthesised. The annealed compacts were isothermally reduced in thermogravimetric apparatus with CO gas at 800–1100°C. The course of reduction was followed by measuring the weight loss as a function of time. X-ray diffraction (XRD), scanning electron microscope (SEM), optical microscope and porosity measurements were used to characterise the annealed and reduced samples. The influence of temperature and basicity (CaO/SiO₂) on the reduction behaviour and the morphology of the annealed samples were investigated. The reduction rate increased with temperature but decreased by increasing basicity value. Metallic iron whisker shape structure was detected in the pure wüstite samples after reduction at high temperatures while in basic wüstite samples, whiskers were formed at the surface of the compacts. From the activation energy values, the reduction of pure wüstite is most likely controlled by a combined effect of gaseous diffusion and interfacial chemical reaction mechanisms. The reduction of basic wüstite compacts with 0·2 and 0·5 basicity ratios are most likely controlled by chemical reaction mechanism while for 0·8 basicity ratio, the reduction rate is most likely controlled by solid state reaction mechanism.