Effect of the Addition of CaO or MgO on the Reduction of Dense Wustite with H₂

Abstract

Dense wustite plates containing CaO or MgO were reduced with H₂ in the temperature range of 670 to 930°C.
The wustite containing CaO was reduced topo-chemically and far faster than pure wustite. The experimental results were analysed by the unreacted core model. The observation of cross sections of partially reduced samples containing CaO makes the following clear. Reduced iron layers containing pores elongated from surface of specimen to interface and the long contact lines between oxide, metal and gasphase are produced by outward growth accelerated by the presence of CaO. It is therefore considered that the acceleration of reduction due to addition of CaO is caused by the formation of reduced iron layer with above mentioned structure.
On the other hand, the wustite containing MgO were reduced slower than pure wustite and majorpart of the surface of specimens were covered by the dense iron film in the initial stage where the reduction rate obeys the rectilinear law. After this stage, the reduced iron phase grows up nontopo-chemically from the uncovered surface and the reduction rate of this stage is larger than that of pure wustite when it obeys palabolic law.