The Reduction Behavior of Synthetic Chromites by Carbon

Abstract

The chromites shown below were prepared synthetically and reduced by graphite powder under a CO atmosphere: FeCr₂O₄ (Sp 1), MgCr₂O₄ (Sp 2), (Fe_0.5Mg_0.5) Cr₂O₄ (Sp 3), (Fe_0.5Mg_0.5) (Cr_0.8Al_0.2) ₂O₄ (Sp 4), and Mg (Cr_0.6Al_0.4) ₂O₄ (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 Cr₂O₃. With the progress of the reduction, the metallic products changed in the following order: Austenite→austenite+ (Fe, Cr) ₃C→ (Fe, Cr) ₃C+ (Cr, Fe) ₇C₃→ (Cr, Fe) ₇C₃.
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 FeCr₂O₄ component, FeO and Cr₂O₃ were reduced simultaneously at temperatures higher than 1150°C, although the reduction of FeO preceded at lower temperatures. The reduction of the MgCr₂O₄component (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 MgCr₂O₄ component of Sp 4 and Sp 5 which contained Al₂O₃was only encountered at temperatures higher than 1330°C.
3) The metallic product of the chromites Sp 3 and Sp 4 was (Cr, Fe) ₇C₃in either reduction stage of the FeCr₂O₄ and MgCr₂O₄ components. The final product of the reduction of the chromites Sp 2 and Sp 5 was Cr₃C₂, while an unidentified phase appeared during the course of the reduction and was considered to be chromium oxycarbide.