The chromites shown below were prepared synthetically and reduced by graphite powder under a CO atmosphere: FeCr
2O
4 (Sp 1), MgCr
2O
4 (Sp 2), (Fe
0.5Mg
0.5) Cr
2O
4 (Sp 3), (Fe
0.5Mg
0.5) (Cr
0.8Al
0.2)
2O
4 (Sp 4), and Mg (Cr
0.6Al
0.4)
2O
4 (Sp 5).
The results obtained are as follows:
1) In the case of the pure iron chromite Sp 1, the reduction of FeO component preceded that of Cr
2O
3. With the progress of the reduction, the metallic products changed in the following order: Austenite→austenite+ (Fe, Cr)
3C→ (Fe, Cr)
3C+ (Cr, Fe)
7C
3→ (Cr, Fe)
7C
3.
2) The reduction of complex chromites containing iron oxide (Sp 3 and Sp 4) took place in two stages. In the first stage with the reduction of the FeCr
2O
4 component, FeO and Cr
2O
3 were reduced simultaneously at temperatures higher than 1150°C, although the reduction of FeO preceded at lower temperatures. The reduction of the MgCr
2O
4component (the second stage) required higher temperatures. It started at 1200°C and proceeded rapidly at temperatures higher than 1250°C in the case of Sp 2 and Sp 3. The rapid progress of the reduction of MgCr
2O
4 component of Sp 4 and Sp 5 which contained Al
2O
3was only encountered at temperatures higher than 1330°C.
3) The metallic product of the chromites Sp 3 and Sp 4 was (Cr, Fe)
7C
3in either reduction stage of the FeCr
2O
4 and MgCr
2O
4 components. The final product of the reduction of the chromites Sp 2 and Sp 5 was Cr
3C
2, while an unidentified phase appeared during the course of the reduction and was considered to be chromium oxycarbide.
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