Ferrite is a metal oxide with ferromagnetism. In terms of electrical properties, the resistivity of ferrite is much larger than that of metal and alloy magnetic materials, and it also has higher dielectric properties. The magnetic properties of ferrite also show high permeability at high frequencies.
Therefore, ferrite has become a non-metallic magnetic material with a wide range of applications in the field of high frequency and weak current. Because the magnetic energy stored in the unit volume of ferrite is low, the saturation magnetization is also low (usually only 1/3 to 1/5 of pure iron), which limits its use in low-frequency strong electric and high magnetic energy density requirements. Applications in high-power fields.
Ferrite belongs to the category of semiconductors in terms of electrical properties, so it is also called a magnetic semiconductor. Magnetite (the main component is Fe3O4) is the simplest type of ferrite. Internationally, ferrite was synthesized as early as the early 20th century. In the 1930s, France, Japan, Germany, and the Netherlands successively carried out systematic research. The Netherlands has been producing ferrite soft magnetic materials since 1946. China began industrial production of ferrite around 1956. Ferrite has been widely used in communications and broadcasting, computing technology, automatic control, radar navigation, astronautics, satellite communications, instrument measurement, printing display, pollution treatment, biomedicine, high-speed transportation, etc. Ferrite is a composite oxide composed of iron and one or more other metals. For example, the chemical formula of spinel ferrite is MeFe2O4 or MeO·Fe2O3, where Me is a divalent metal ion with an ion radius similar to ferrous ion (Fe2+) (such as Mn2+, Zn2+, Cu2+, Ni2+, Mg2+, Co2+, etc.) ) Or a group of multiple metal ions whose average chemical valence is divalent.
Ferrite is divided into soft ferrite and permanent ferrite.
1. Soft ferrite includes manganese ferrite (MnO Fe2O3), zinc ferrite (ZnO Fe2O3), nickel zinc ferrite (Ni-Zn Fe2O4), manganese magnesium zinc ferrite (Mn-Mg) -Zn·Fe2O4) and other single-component or multi-component ferrites. The resistivity is much larger than that of metallic magnetic materials, and they have higher dielectric properties. Therefore, ferrites with ferromagnetism and ferroelectricity, as well as ferromagnetism and piezoelectricity, appear. At high frequencies, it has a much higher magnetic permeability than metal magnetic materials (including iron-nickel alloys, aluminum-silicon-iron alloys), and is suitable for working at frequencies of several kilohertz to several hundred megahertz. Processing ferrite belongs to a general ceramic process, so the process is simple, and a lot of precious metals are saved, and the cost is low. The saturation magnetic flux density Bs of ferrite is low, usually only 1/3 to 1/5 of that of iron. Ferrite has low magnetic energy stored per unit volume, which limits its application in low-frequency, high-power and high-power fields that require higher magnetic energy density. It is more suitable for high frequency, low power, and weak current applications. Nickel-zinc ferrite can be used as the antenna magnetic rod in the radio and the magnetic core of the intermediate frequency transformer, and the manganese-zinc ferrite can be used as the line output transformer core in the TV receiver. In addition, soft ferrites are also used in the magnetic cores of intensifiers and filters in communication lines. In recent years, it has also been used as a high-frequency magnetic recording transducer (magnetic head).
2. Permanent ferrite includes barium ferrite (BaO·6Fe2O3) and strontium ferrite (SrO·6Fe2O3). It has high resistivity and belongs to the semiconductor type, so the eddy current loss is small, the coercive force is large, and it can be effectively used in the magnetic circuit of the large gap. It is especially suitable for the permanent magnet of small generators and motors. It does not contain precious metals such as nickel, cobalt, etc. It has a rich source of raw materials, an uncomplicated process, and low cost. It can replace AlNiCo permanent magnets. Its maximum magnetic energy product (B+H)m is low, so under the same magnetic energy, it is larger than a metal magnet. Its temperature stability is poor, the texture is brittle, fragile, and it is not resistant to shock and vibration. It is not suitable for measuring instruments and magnetic devices with precision requirements. Permanent ferrite products are mainly anisotropic series. They can be used to make permanent magnet ignition motors, permanent magnet motors, permanent magnet concentrators, permanent magnet suspension heads, magnetic thrust bearings, magnetic separators, speakers, microwave devices, magnetic therapy tablets, hearing aids, etc.