Morphology Control of Metallic Iron Formed by Hydrogen Reduction of Iron Oxide

Abstract

To clarify the sticking mechanism and discuss its suppression during hydrogen reduction in the fluidized bed, in-situ observation of the reduction behavior of wüstite using high-temperature microscope and the reduction experiment were carried out under various conditions such as gas composition, temperature, and total pressure.

First, hydrogen reduction leads to the formation of porous structure of wüstite phase. Then, reduction to metallic iron proceeds concentrically, and porous iron forms. A part of metallic iron nuclei grows vertically to the wüstite surface, and iron whisker forms under specific conditions. Under atmospheric pressure conditions, higher temperature and higher hydrogen partial pressure make the surface porous, and iron whisker forms through 100%H₂ reduction at 900°C and 950°C. Increasing total pressure enlarges the formation area of iron whiskers to lower temperature. Furthermore, three-step fluidized bed reduction process was suggested to control the sticking phenomenon of raw materials.