Kinetics of Re-oxidation of the Sponge-Iron Powders

Abstract

Kinetic studies of the re-oxidation of the sponge-iron powders reduced in the temperature range 400 to 800°C from ferric oxides and Brazilian iron-ores have been carried out at various partial pressures of oxygen in the temperature range 300 to 800°C.
The characteristics of the sponge-irons during oxidation have been determined by means of four methods (gravimetric, microscopic examinations, X-ray diffraction and surface area measurements). Following results were obtained.
1) Oxidation of sponge-irons proceeds very rapidly by exposure to oxidizing atmosphere and then proceeds slowly. The latter obeys logarithmic law.
2) As those sponge-irons are oxidized, their specific surface areas increase and then decrease gradually.
3) The structure of the oxide layers are examined by X-ray diffraction; generally, magnetite is observed as a main component, accompanying small amounts of hematite.
4) The early rapid re-oxidation is regarded as gaseous diffusion control and latter slow oxidation obeys the logarithmic oxidation law.