The nucleation and growth of the iron phase on wustite during the reduction with H
2-N
2 or CO-N
2 at 650∼850°C and the properties of iron reduced were investigated.
The results obtained are as follows:
(1) The nuclei originated from pores and edges on the wustite surface in the H
2-N
2 reduction. On the other hand, they originated mostly from edges in the CO-N
2 reduction. In either gases an iron nucleus on wustite grew linearly against the reduction time.
(2) The rate of iron growth on wustite was proportional to
PH2 in the range of
PH2=0∼0.2 atm. The reproducibility of the rate of iron growth in CO-N
2 was worse than that of H
2-N
2 reduction. The rate of iron growth was proportional to
PCO in the range of
PCO=0∼0.8 atm and kept nearly constant over
PCO=0.8 atm.
(3) The apparent activation energy for iron growth on the wustite surface was about 14 kcal/mol in H
2 and fluctuated in the range of 16∼32 kcal/mol with CO concentration in CO-N
2. The rate of iron growth in H
2 was nearly 40 times larger than that of CO at the same partial pressure of reducing gas.
(4) The iron reduced in H
2 was very dense at the FeO/Fe interface and the iron growth into the wustite bulk was not appreciable. On the other hand, the iron reduced in CO was porous and the iron growth into the wustite bulk was remarkable.
(5) The rate of iron growth in H
2 was controlled by an interfacial reaction at the FeO/Fe/H
2-three phase boundary on the wustite surface. At the beginning of CO reduction the iron growth took place at the FeO/Fe interface both on the surface and inside the specimen, because the porous structure of iron and CO
2 formed by the reduction of FeO affected the rate of iron growth on wustite. Wide scattering of the data of iron growth in CO reduction may be attributed to the effect of CO
2 from the FeO/Fe interface inside the FeO bulk.
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