Metallic iron whisker formation and growth during iron oxide reduction: K 2 O effect

Abstract

An attempt has been made to clarify metallic iron whisker growth and swelling behaviour during iron oxide reduction in the presence of K₂O alkali. Annealed pure and K₂O doped wüstite compacts were isothermally reduced in a thermogravimetric apparatus with CO gas at 800–1100°C. The reduction rate increased with temperature but decreased with increasing K₂O content. Morphologically, by increasing reduction temperature, porosity and whisker growth of the metallic iron produced increased, which in turn leads to the apparent swelling and compact disintegration. The reduction of pure wüstite at both the initial and final stages is most likely controlled by a combined effect of gaseous diffusion and interfacial chemical reaction mechanisms. For K₂O doped wüstite samples, the reduction at the initial stages is most likely controlled by gaseous diffusion mechanism, while in the final stages, it is most likely controlled by a chemical reaction mechanism.