Study On Solid Phase Interfacial Reaction Behavior Of Chromium/Titanium Oxide-Calcium Ferrite System

For a long time,China has faced the problems of insufficient chrome ore resources and tight supply and demand.At the same time,steel companies have higher requirements of the self-produced iron ore.The high-chromium vanadium-titanium magnetite in the Panxi region of China is large reserves and high chromium content,which has the great economic and strategic potential for development and utilization.In the sintering-blast furnace process,the sinter quality of high-chromium vanadium-titanium magnetite is poor.Therefore,the basic research on the sintering mechanism of high-chromium vanadium-titanium magnetite and the improvement of the sintering quality of high-chromium vanadium-titanium ore are the keys to the efficient use of high-chromium vanadium-titanium magnetite in the sintering-blast furnace process.In this paper,the effects of holding time,temperature and atmosphere on the solid-phase interfacial reactions of Cr2O3-calcium ferrite and TiO2-calcium ferrite systems were studied by diffusion couple method which may occur during the sintering process.The experiments were characterized by thermodynamic calculation,X-ray diffraction(XRD),scanning electron microscopy(SEM)and energy spectrum analysis(EDS).The reaction mechanism of the solid-phase interfacial reactions was explored.The interdiffusion coefficient was calculated by the Wagner equation.The experimental results showed that:(1)In the solid phase reaction of Cr2O3-calcium ferrite system/TiO2-calcium ferrite system at 1373-1473K,the diffusion of Ca2+ into the Cr2O3/TiO2 layer is the driving force of.the solid phase reaction.And the diffusion of Ca2+ within the calcium ferrite layer is a limiting part of the solid phase reaction.The relationship between the product layer thickness and the time square of the system conforms to the parabolic law,and the solid phase reaction is the diffusion control rate.(2)CaCr2O4 and CaTiO3,as the solid-phase interfacial reaction products of Cr2O3-calcium ferrite system and TiO2-calcium ferrite system respectively,improve the liquidus temperature of the sinter and reduce the reducibility of sinter,thereby reduce the sinter quality.(3)The interdiffusion coefficient of Cr2O3-calcium ferrite system is in the range of 10-10～10-12cm2/s,and the interdiffusion coefficient of TiO2-calcium ferrite system is in the order of 10-13～10-11cm2/s at 1373-1473K.The interdiffusion coefficients of both systems increase with the increasing temperature and decrease with increasing holding time.The interdiffusion coefficient in the product layer is greater than that in the reactant.(4)The oxygen in air promotes the mass transfer,and the products thickness and interdiffusion coefficient of the two systems in the nitrogen atmosphere is small.The oxygen in the air has a more pronounced effect on the Cr2O3-calcium ferrite system.(5)Under the same temperature system,the product layer thickness and interdiffusion coefficient of Cr2O3-calcium ferrite system are larger than those of TiO2-calcium ferrite system.Both Cr and Ti combine with Ca in calcium ferrite,but Cr has a stronger ability.In the solid phase reaction stage during the sintering process,the high-chromium vanadium-titanium magnetite has a lower sinter quality than the ordinary vanadium-titanium magnetite due to the higher Cr content.