Preparation And Properties Of High Performance Permanent Magnet Strontium Ferrite （SrM）

SrM permanent magnet ferrite is a magnetic material manufactured by a series of related ceramic processes such as pre-sintering,molding,ball milling,and sintering,with Sr O and Fe₂O₃as the basic raw materials.It has high coercivity,high remanence,and high magnetic energy.Product,high magnetic flux density,high Curie temperature and good corrosion resistance.In recent years,with the rapid development of electronic information technology and new energy industry,it has been widely used in many controllers,electrical instruments,automobiles,motors,etc.However,the development status of China’s many strontium ferrite products but the lack of high-performance products seems to be powerless in the face of the complicated international situation and the rapid development of the new energy industry.Therefore,the preparation and performance research of high-performance permanent magnet strontium ferrite（SrM）has been urgent.In this paper,sintered ferrite magnets were prepared through the control of ion substitution,process and additives,and their morphology,structure and magnetic properties were explored,which are mainly divided into the following aspects:1.Study the effects of different substitution elements Ca,La,Co and different substitution amounts and iron-deficient formulations on the magnetic properties.The results of microstructure characterization and magnetic properties measurement show that:（1）La³⁺substitution can increase the total magnetic moment and magnetocrystalline anisotropy of the unit cell,make the grains appear flaky,the sintered magnet has a good squareness;（2）Ca²⁺substitution can improve the density of the sintered body,magnetocrystalline anisotropy,and cause Fe³⁺-O^2-The change of the superexchange effect between the two,proper addition can improve the remanence and coercivity;（3）Co²⁺substitution will increase the saturation magnetization,but excessive addition will reduce the coercivity;（4）The iron deficiency formula is the best way to improve the coercivity.One of the important means of coercivity,the reduction of Fe content produces Fe³⁺vacancies and O^2-,which improves the magnetocrystalline anisotropy.Finally,considering the comprehensive properties of remane,coercivity,maximum magnetic energy product and squareness,the main formula is selected as Sr_0.36Ca_0.25La_0.39Co_0.3Fe_10.8O₁₉.2.The preparation process of SrM was studied on the basis of different ion substitutions to clarify the main formula.The results show that:（1）Determine the pre-sintering temperature of 1250℃,the pre-sintered powder has higher activity and specific saturation magnetization,and has a good effect on remanence and correction.The coercive force is favorable;（2）The secondary ball milling for 16h has relatively narrow particle distribution and small grain size;（3）The sintering temperature of1200℃is determined,and the magnet has a high density and no abnormally grown crystals The granules are sintered at a stepped temperature,which can improve the sintering efficiency and the sample has no cracking.By exploring the process,a sample with good performance was obtained:B_r=4418 Gs,H_cj=4555 Oe,（BH）_max=4.67 MGOe.（4）The post-doping process can improve the grain uniformity,thereby improving the squareness,and control the diameter/thickness ratio of the grains at 1.5～2.4,reaching 90%and above,and obtaining samples with good properties:B_r=4418 Gs,（BH）_max=4.52 MGOe,H_k/H_cj=0.90.3.Through the research on additives and dispersants,the results show that:（1）Adding Ca CO₃promotes the solid phase reaction and increases the density of sintered magnets,but excessive addition leads to abnormal grain growth,which is not good for coercivity;（2）Si O₂can effectively inhibit the grain growth,but excessive addition will generate a non-magnetic phase and reduce the saturation magnetization;（3）The addition of H₃BO₃has a significant effect on the modification of grain boundaries and improves the squareness,but excessive addition will cause As the grain grows,the coercivity decreases.Through experiments,the combination additive0.5 wt%Ca CO₃+0.3 wt%Si O₂+0.3 wt%sorbitol.4.By adding the raw materials of the corresponding formula in the second ball milling and adding the corresponding formula raw materials in the first ball milling,the results show that:（1）Adding the corresponding raw materials according to the formula in the second ball milling can improve the grain uniformity without sharp corners,in flake shape,and the average diameter thickness is about In the range of 1.5～2.4,H_k/H_cj≥90%.Good sample properties were obtained:B_r=4418 Gs,（BH）_max=4.52 MGOe,H_k/H_cj=0.90.（2）Adding a certain mass fraction of La（OH）₃in the secondary ball milling process,the properties of the sintered magnet are:B_r=4518 Gs,H_cj=3061 Oe,（BH）_max=4.98 MGOe,H_k/H_cj=0.88.