Observation of diffusion behavior between Cr2O3 and calcium ferrite based on diffusion couple method at 1373 K

Abstract

The existence of Cr2O3 has an effect on the quality of high-chromium vanadium-titanium magnetite sinter. In order to investigate the influence of Cr2O3 on the quality of sinter in the solid-phase reaction stage of sintering process, the solid-phase reactions of Cr2O3-calcium ferrite (CF) system at 1373 K in air at different times were studied by diffusion couple method. The change of diffusion interface and the migration of Ca, Cr and Fe were observed by emission scanning electron microscopy. The results show that in the process of diffusion, the diffusion thickness of Ca2+ in CF layer was 10.22 μm, and that of Ca2+ in Cr2O3-CF diffusion couple was 57.65 μm at 1373 K for 8 h. The relationship between the thickness of the product layer and time at 1373 K for 0 h–20 h was obtained. The diffusion of Ca2+ to the Cr2O3 layer is the driving force of the solid phase reaction, and the diffusion of Ca2+ in the ferrite layer is the limiting link of the solid phase reaction, the order of magnitude of diffusion coefficient of Cr2O3-CF diffusion couple was 10−11 cm2 s−1. Ca2+ in calcium ferrite is likely to combine with Cr3+ to form CaCr2O4. The production of calcium ferrite will be reduced when Cr2O3 is present in sintering material. Meanwhile, the solid phase product CaCr2O4 in the diffusion process has the properties of high melting point and difficult reduction. The shortage of liquid phase due to high melting point and the difficulty in reduction may affect the quality of sinter.