Abstract:

During sintering the vanadium titanomagnetite， TiO₂ competes with Fe₂O₃ for CaO， which inhibits the formation of calcium ferrite （C _x F） and affects the sinter quality. In this paper， the diffusion reaction of CaO-Fe₂O₃-TiO₂ system is intuitively studied by preparing C _x F/TiO₂ diffusion couple. Electron probe and X-ray diffractometer are used to analyze and characterize the products at different positions of the reaction interface. The reaction characteristics of C _x F/TiO₂ interface are studied at the diffusion temperature of 900~1050 ℃ and the time of 1~4 h. The effects of temperature and time on the types， distribution and morphology of the generated phases are discussed. The results show that the main phases are C _x F， CaO·Fe₂O₃（CF）， Fe₂O₃， CaTiO₃ and TiO₂ from the C _x F- to TiO₂-layer， among which perovskite （CaTiO₃） is the main product. The thickness of CaTiO₃ increases from 8.1 μm to 90.2 μm with the temperature increasing from 900 ℃ to 1 050 ℃； it increases from 47.4 μm to 121.4 μm with the time increasing from 1 h to 4 h. Meanwhile， the diffusion thickness of CaTiO₃ has a good linear relationship with the square root of diffusion time， which indicates that the formation of CaTiO₃ is controlled by diffusion process. Furthermore， the formation process of CaTiO₃ in CaO-Fe₂O₃-TiO₂ system is explained by vacancy-mediated diffusion mechanism.

Key words: calcium ferrite, TiO₂, diffusion couple, diffusion thickness, vacancy-mediated diffusion mechanism