Study On Morphology And Properties Of Magnetic Powders For Bonded Ferrite Magnets

Due to its higher coercivity 、 stronger magnetic anisotropy and larger saturation magnetization,etc.M-type hexagonal ferrite has become more important magnetic materials in all fields.Bonded ferrite magnet has a certain shape and size in the different molding way,which is made by mixing M type ferrite powder and various additives binders.To make the performance of magnets meet actual requirements,the suitability of the magnetic powder in the molding process should be very important in the preparation process of magnetic powder.In this paper,according to the calendering molding process and injection molding process on different requirements of magnetic particle morphology,two types of magnetic powders have been prepared for bonded ferrite magnet.The control of morphology and size of magnetic powders was accomplished by the addition of cosolvent,and magnetic performance should not be damaged,especially the saturation magnetization.The aspect ratios of magnetic powder particles are about 5 for calendering molding process,this only is a empirical value.The magnetic powder particles are nearly spherical shape for injection molding process.In this paper,the solid phase reaction method and the twice calcining method wre used to prepared magnetic powder for bonded ferrite magnets.The magnetic properties,morphology and phase composition of the samples were studied.The main work in this article can be summarized as follows :1. When n(Fe content) is 5.5 and 5.6, the magnetic particles grow easily in the radial direction, and when n is 5.7 and 5.8, the magnetic particles grow easily along the c-axis direction.2. The magnetic powders of the bonded ferrite magnet for calendering molding process:(1) The size and the acpect ratio of the magnetic powder particles can be controlled by adding the single cosolvent, and without reducing the magnetic properties.The typical experimental results are as follow: LaxSr1-xZnxFe2n-xO19(x=0.26,n=5.5): with adding cosolvent E,the aspect ratios of magnetic powder particles are about 5, the magnetic properties are: Hcj=3.09 kOe, ?20=66.4 emu/g, ?r=34.8 emu/g.(2) The size and the acpect ratio of the magnetic powder particles can be also adjusted by adding double cosolvents combination and altering the calcining temperature, and without reducing the magnetic properties. The typical experimental results are: LaxSr1-xZnxFe2n-xO19(x=0.26,n=5.6): with adding double cosolvents combination J, the aspect ratios of magnetic powder particles are about 5, the magnetic properties are: Hcj=2.49 kOe, ?20=63.2 emu/g, ?r=35.9 emu/g.(3) The addition of three kinds of cosolvents combination can also adjust and control the morphology and size of the magnetic particles, and magnetic particles that the acpect ratio is about 5 can be obtained. However, due to the choice of temperature or other reasons, the desired magnetic properties can not be obtained.3. The magnetic powders of the bonded ferrite magnet for injection molding process:The spherical magnetic particles that are suitable for injection molding process can be obtained by adjusting technology and adding the cosolvent.The typical experimental results are: LaxSr1-xZnxFe2n-xO19(x=0.26,n=5.6): with adding cosolvent K, the shape of the magnetic powder particles are nearly spherical, the magnetic properties are: Hcj=3.04 kOe, ?20=69.0 emu/g, ?r=35.9 emu/g.