Study On Preparation Technology Of M-type Strontium Ferrite Permanent Magnetic Materials

M-type permanent magnet ferrite is widely applied in new-energy vehicles,smart home,and other emerging industries of strategic importance because of it's higher coercivity,higher saturation magnetization and lower production price.However,with the enhancement of people's awareness of environmental protection and the rapid development of micromotors,the existing permanent magnet ferrite materials in the market are increasingly difficult to meet the actual needs.Therefore,it is of practical significance to study high-performance M-type ferrite materials.M-type strontium ferrite was prepared by solid-state reaction.A comprehensive exploration of relationship between ion substitution,iron deficiency formula and preparation technology with the phase,microstructure and magnetic properties were performed.Firstly,La substitution,La-Ca substitution and La-Co substitution are synthesized by solid-state reaction,and the influences from each component of composition on the properties of M-type strontium ferrites were investigated.The results show that:?1?La substitution has a certain effect on the phase and microstructure of the material.When the substitution amount x is more than 0.5,the miscellaneous phase?-Fe₂O₃ begins to appear.The inhibition of La³⁺on grain growth results in the decrease of average grain size D.With the increase of substitution x,the residual magnetic induction intensity B_r,saturation magnetization 4?M_s and maximum magnetic energy product?BH?_maxax decrease gradually.?2?La-Ca substitution has a great influence on the phase and magnetic properties of the material.When x is more than 0.2,the impurity phase?-Fe₂O₃ has already appeared in the sample.The residual magnetic induction B_r and saturation magnetization 4?M_s increase first and then decrease with the increase of substitution x.When x equals 0.2,the maximum values are 4359Gs and 4510Gs respectively.?3?La-Co substitution has little effect on the phase of the material.In the range of x=0.0⁰.5,all six groups of pre-sintered materials produce single M-phase.The residual magnetic induction B_r and saturation magnetization 4?M_s increase first and then decrease with the increase of substitution x,reaching the maximum values of 4285Gs and 4599Gs at x=0.3,respectively.The magnetic induction coercivity H_cb and intrinsic coercivity H_cj gradually increase with the increase of substitution amount x,reaching the maximum values of 2082 Oe and 2353 Oe at x=0.5,respectively.Secondly,on the basis of the three ion substitutions,the main formula was further optimized,and two factors and four levels of orthogonal experiment and iron deficiency formula experiment were designed.The results show that:?1?When La-Ca-Co is substituted,the effect of factor X?La-Ca substitution?on each parameter is greater than that of factor Y?Co substitution?,but the optimal formula of each parameter is different.Under the formula of X₄Y₁(Sr_0.3La_0.35Ca_0.35Fe_11.9Co_0.1O_19-?),the magnetic properties of the sintered body are relatively high:B_r=4265Gs,H_cj=3022Oe,and?BH?_max=4.4MGOe.?2?Suitable iron deficiency is beneficial to the formation of single M-type phase.When iron deficiency is less than 0.25,the residual magnetic induction intensity B_r and saturation magnetization intensity 4?M_s are increasing.However,iron deficiency is not conducive to the improvement of coercivity.Finally,after determining the main formula,the process?pre-sintering temperature,second grinding time,forming magnetic field and forming pressure?was further explored.The results show that:?1?Pre-sintering temperature has little effect on residual magnetic induction B_r and saturation magnetization 4?M_s,but it will affect coercivity.The coercivity decreases gradually with the increase of pre-sintering temperature in the range of 1200?¹280?.?2?Increasing the second grinding time will reduce the particle size,magnetic induction coercivity H_cb and intrinsic coercivity H_cj of the second grinding slurry.The residual magnetic induction B_r and saturation magnetization 4?M_s first increase and then decrease with t increasing.When t=10h,B_r and 4?M_s reach their maximum values,4229Gs and 4323Gs respectively.?3?Increasing the forming magnetic field is beneficial to increase the residual magnetic induction intensity B_r and saturation magnetization of 4?M_s.When H=10000Oe,the maximum values of B_r and 4?M_s are 4138Gs and 4332Gs respectively,while the magnetic induction coercivity H_cb and intrinsic coercivity H_cj will gradually decrease with the increase of the forming magnetic field.?4?The forming pressure will affect the green density d₁ of the sample.With the increasing of the forming pressure d₁ will gradually increase,but the sintering densities d₂,B_r,4?M_s,H_cb and H_cj have no obvious change trend.