Initial Stage of Reduction of Dense Wustite

Abstract

The reduction of dense wustite crystals quenched from the molten state has been studied over the temperature range from 600° to 1 00°C in order to investigate the rate controlling step of the intial stage of reduction. The reduction rate was calculated from the weight change of the specimen measured by a thermobalance. The change in iron concentration and the rerief of the surface of specimen with time were observed with an Electron Probe Micro-Analyzer (EPMA) and an optical microscope. The reduction rate was expressed by the rectilinear law R=k₁t at the initial stage, and then by the parabolic law R=k₂t^1/2 at the middle stage of reduction process.
As long as the rectilinear law was valid, the number of point-like reduced irons increased on the surface of specimen. As the reduction proceeded furthermore, the diameter of point-like reduced irons became large. When the point-like irons were contacted with each other, the specimen surface was completely covered with reduction iron. When the surface of specimen was covered with reduction iron, the reduction rate equation was changed to the paraboric law.
It is concluded that the overall reduction rate can not be expressed by only one general equation for dense iron oxide, “Fe O”, because the micro-mechanism of the reduction process is not same for these three stages.