Abstract
Sulphur in reducing gas was found to be the only essential factor to cause abnormal swelling (volumetric increase of about 500 percentage) of hematite and magnetite pellets even in the reduction with hydrogen. This swelling brought about by the formation of iron whiskers was significant when the activity of sulphur relative to iron/iron sulphide equilibrium was in the range of 10-3 1 and the feed rate of reducing gas was so small as to control the reduction rates.
The effects of reduction temperature, PH2O/PH2, ratio and indurating temperature of hematite pellets on this swelling due to sulphur was also investigated.
The conditions indispensable to the formation of iron whiskers were found to be the presence of sulphur of low potential and the relatively slow rates of chemical reaction on the surface of wustite. This was independent of the kind of reducing gas.
In the absence of sulphur, the addition of CaO into iron oxides can not induce the abnormal swelling but general swelling (volumetric increase of several tens of percentage), regardless of any reduction histories to wustite. But, the less uniform its distribution in iron oxides, the greater the abnormal swelling by sulphur.
