Reaction Mechanism Of M-type Strontium Ferrite Prepared From Bayan Obo Super Iron Concentrate By Microwave Sintering

Bayan Obo super iron concentrate contains RE,Nb and other elements,which can be used as high quality raw materials for powder metallurgy,magnetic materials and clean steel production.In this paper,M-type strontium ferrites were separately synthesized by methods of conventional sintering and microwave sintering with Bayan Obo super iron concentrate.The optimum conditions of preparation of M-type strontium ferrites were obtained by means of XRD,FTIR,SEM-EDS and VSM,the controlling steps and reaction mechanism of different stage of the synthesis process were found out through the calculation of the sintering reaction kinetics,which provides a new way for the high-value utilization of Bayan Obo iron ore.The experimental results of synthesis of M-type strontium ferrites show that under the condition of microwave sintering temperature of 1100?and holding time of 1.5h,the optimal magnetic properties are obtained,and the saturation magnetization?M_S?,remanent magnetization?M_r?and coercivity?H_C?are 71.74emu/g,35.60emu/g and 3967.1Oe respectively.While under the conditions of conventional sintering at 1200?and holding time of 3h,the magnetic properties of the sample are the best,the saturation magnetization?M_S?,remanent magnetization?M_r?and coercivity?H_C?of the sample are 71.89emu/g,36.32emu/g and 3826.7Oe respectively.By comparison,it can be seen that the M_S of M-type strontium ferrite prepared by the different sintering techniques is not much different,but the sample prepared by microwave sintering technique has higher H_C,lower required temperature and shorter time.The analysis results of Non-isothermal kinetics of sintering process show that under the microwave sintering method,the reaction process can be divided into three stages.The oxidation stage of Fe₃O₄ is in 230-480?,which belongs to the reaction control of three-dimensional diffusion,and the apparent activation energy is 83-89kJ/mol;the decomposition stage of SrCO₃ is in the temperature range of 480?to 730?,which belongs to the reaction control of three-dimensional diffusion,and the apparent activation energy is 192-203kJ/mol;the rapid generation stage of SrFe₁₂O₁₉ is in the temperature range of 730?to 1300?,which conforms to the Avrami-Erofeev equation and belongs to the reaction control of random nucleation and subsequent growth,and the apparent activation energy is 277-279kJ/mol.While under the conventional sintering method,the reaction process can be divided into four stages.The oxidation of Fe₃O₄ is in the temperature range of 200?to 670?,which belongs to three-dimensional diffusion at the initial stage of the reaction and then enter the nucleation growth stage;the decomposition stage of SrCO₃ is in the temperature range of 670?to 840?,which belongs to the reaction control of three-dimensional diffusion,and the apparent activation energy is559-560kJ/mol;the generation stage of SrFeO_3-x and SrFe₁₂O₁₉ is in the temperature range of 840?to 1000?,which conforms to the Avrami-Erofeev equation and belongs to the reaction control of random nucleation and subsequent growth,and the apparent activation energy is 1144-1151kJ/mol;the rapid generation stage of SrFe₁₂O₁₉ is in the temperature range of 1000?to 1230?,which conforms to the Avrami-Erofeev equation and belongs to the reaction control of random nucleation and subsequent growth,and the apparent activation energy is 1730-1734kJ/mol.Comparing the calculation results of reaction kinetics under the different sintering methods,microwave sintering can significantly reduce the activation energy of the reaction,and realize low-temperature rapid sintering.