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Views: 0 Author: Site Editor Publish Time: 2022-09-05 Origin: Site
Ferrite magnet is a permanent magnet mainly made of SrO or BaO and Fe2O3 as raw materials. Compared to other permanent magnets, ferrite magnets are hard and brittle, with lower magnetic energy. However, it is not easy to demagnetize and is not easy to corrode, the production process is simple and the price is low. Therefore, the output of ferrite magnets in the entire magnet industry is relatively high and is widely used in industrial production. Ferrite is a non-metallic magnetic material, also known as ferrite. It is prepared and sintered by ferric oxide and one or several other metal oxides (such as nickel oxide, zinc oxide, manganese oxide, magnesium oxide, barium oxide, strontium oxide, etc.). Its relative magnetic permeability can be as high as several thousand, its resistivity is 1011 times that of metal, and its eddy current loss is small, so it is suitable for making high-frequency electromagnetic devices.
There are five types of ferrites: hard magnetism, soft magnetism, moment magnetism, gyromagnetism and piezoelectric magnetism. Formerly known as iron oxide magnet or iron oxide, its production process and appearance are similar to ceramics, so it is also called magnetic porcelain. Ferrites are complex oxides of iron and one or more other suitable metal elements. It is semiconducting in nature and is usually used as a magnetic medium. The most important difference between ferrite magnetic materials and metal or alloy magnetic materials is electrical conductivity. Usually the resistivity of the former is 102～108Ω·cm, while the latter is only 10-6～10-4Ω·cm.
Ferrite magnets are produced by powder metallurgy, with low remanence and low recovery magnetic permeability. The coercive force is large and the anti-demagnetization ability is strong, which is especially suitable for the magnetic circuit structure used in dynamic working conditions. The material is hard and brittle and can be used for cutting with emery tools.
The main raw material is oxide, so it is not easy to corrode. Operating temperature: -40°C to +200°C. Ferrite magnets are further divided into anisotropy (anisotropy) and isotropy (isotropy). The magnetic properties of isotropic sintered ferrite permanent magnet materials are weak, but they can be magnetized in different directions of the magnet; anisotropic sintered ferrite permanent magnet materials have strong magnetic properties, but only along the direction of the magnet Magnetize in a predetermined magnetization direction.
In the actual production of ferrite magnets, raw materials with good chemical composition may not always be able to obtain ferrite magnets with good performance and microstructure. The reason is the influence of physical properties. The listed physical properties of iron oxide include average particle size APS, specific surface area SSA and bulk density BD. Since iron oxide accounts for about 70% of the formula of manganese-zinc ferrite magnet, its APS value has a great influence on the APS value of ferrite magnet powder.
Generally speaking, the APS value of iron oxide is small, and the APS value of ferrite magnet powder is also small, which is beneficial to speed up the chemical reaction. However, considering that the powder particles are too fine, it is not conducive to the subsequent pressing and sintering, and the APS value should not be too small. Obviously, when the APS value of iron oxide is too large, during pre-sintering, due to the large particle size, only the diffusion reaction of the spinel phase can be carried out, and the grain growth process cannot be further carried out. This inevitably leads to an increase in the activation energy required for sintering, which is not conducive to the solid-phase reaction.
