Mechanisms of porous iron growth on wustite and magnetite during gaseous reduction

Abstract

The iron/iron oxide interface morphologies formed during the reduction of dense wustite and magnetite samples have been examined using scanning electron microscopy. Under conditions where porous iron products are obtained, a range of structures, which depend critically on the gas composition, reaction temperature, and bulk oxide composition, may be formed at the inter-face during reduction. Three principal mechanisms of porous iron growth have been identified: (1) a continuous coupled reaction, involving cooperative pore and iron growth, (2) a continuous dendritic growth mechanism, in which pores advance ahead of the iron formation, and (3) a discontinuous mechanism, involving the successive formation and breakdown of dense iron lay-ers on the oxide surface. The reaction mechanisms are explained in terms of the relative mag-nitudes of the various chemical reactions and mass transport processes which occur during the decomposition of the solids.