Metallic iron whisker formation and growth during iron oxide reduction: K2O effect

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 wustite compacts were isothermally reduced in a thermogravimetric apparatus with CO gas at 800-1100 degrees 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 wustite 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 wustite 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.