In the actual production of
ferrite magnets, using raw materials with good chemical composition may can not produce ferrite magnets with good properties and good microstructure. This result is affected by the physical properties. The physical properties of iron oxides include the average particle size (APS), the specific surface area (SSA) and the bulk density (BD). In the formula of Mn Zn ferrite magnet, iron oxide accounts for about 70%. Therefore, its APS value has a great influence on the that value of ferrite magnet powder. Generally speaking, the smaller the APS value of iron oxide is, the smaller the APS value of ferrite magnet powder is, which is beneficial to quicken the speed of chemical reaction. Considering that the fine particle size is not beneficial to the press in the following process and to sinter the crystal, the APS value is not suitable to be too small.
Obviously, during precalcining, when the APS value of iron oxide is too large, due to the larger particle size, only the diffusion reaction of spinel phase can be carried out. The grain growth process can not be further carried out. This will inevitably lead to an increase in activation energy for sintering, which is not conducive to solid phase reaction.
Ferrite magnet is a metal oxide with ferromagnetism. In terms of electrical characteristic, the electrical resistivity of ferrite is much stronger than that of metal and alloy. It also has higher dielectric property. The magnetic properties of ferrites also show that it has high magnetic conductivity at high frequencies. Therefore, ferrite has become a non-metallic magnetic material which is widely used in the field of high frequency and weak current. It belongs to non-metallic magnetic material, which is a compound oxide (or ferrate) of magnetic ferric oxide and one or many other metal oxides. The magnetic force is usually about 800-1000 Gauss, which is often used for voice boxes, loudspeakers and other instruments. The advantages of NdFeB magnet are high cost performance and good mechanical properties; the shortcomings are that it has low Curie temperature point, poor temperature characteristic ,and it is easy to powder and corrode. Only by adjusting its chemical composition and adopting surface treatment methods can the shortcomings be improved so as to meet the requirements of practical application. NdFeB is the third generation rare earth permanent magne, which has the characteristics of small size, light weight and strong magnetic properties. It is the best cost performance at present, and is known as the king of magnet in the field of magnetism. The advantages of high energy density make NdFeB permanent magnetic materials widely used in modern industry and electronic technology. Under the condition of bare magnet, the magnetic force can reach to around 3500 Gauss.
