A ferrite is a ceramic material made by mixing and firing iron with a large proportion (III) oxide (Fe 2 O 3 , rust) small proportions of one or more additional metal elements, such as barium, manganese, nickel, and zinc. Both are electrically non-conductive, meaning that they are isolators, and ferrimagnetic, which means they can easily become magnets or are attracted to magnets. Ferrites can be divided into two families based on their resilience to become magnetic (magnetic coercivity).
Fierce hardness has high coercivity, making it difficult to experience magnetic damage. They are used to make permanent magnets for refrigerator magnets, loudspeakers, small electric motors, and so on.
Soft ferrites have low coercivity, thus easily altering their magnetization, and acting as magnetic field conductors. They are used in the electronics industry to create efficient magnetic cores called ferrite cores for inductors and high frequency transformers, and in various microwave components.
The ferrite compound has a very low cost, made of mostly rusted iron (iron oxide), and also has excellent corrosion resistance. They are very stable and difficult to destroy, and can be made with high and low coercive forces. Yogoro Kato and Takeshi Takei from Tokyo Institute of Technology synthesized the first ferrite compound in 1930.
Video Ferrite (magnet)
Composition, structure, and properties
Ferrites are usually ferrimagnetic ceramic compounds derived from iron oxide. Magnetite (Fe 3 O 4 ) is a well-known example. Like most ceramics, ferrite is a hard, brittle, and poor electrical conductor.
Many ferrites adopt a spinel structure of the formula AB 2 O 4 , where A and B represent various metal cations, usually including iron (Fe). The ferrite spinel usually adopts a crystal motif consisting of cubic oxide (fcc) (O 2 - ) with a cation which occupies one-eighth of the tetrahedral hole and the B cation which occupies half of the octahedral hole ie < span> A 2 B 3
2 O 2 -
4 .
The ferrite crystals do not adopt the usual spinel structure, but the inverted spinel structure: one-eighth of the tetrahedral hole is occupied by B cations, one quarter of the octahedral sites are occupied by A. cations and the other one quarter by the Basi. It is also possible to have mixed structure spinel ferrites with the formula [M 2 1 -? Fe 3 ? ] [M 2 ? Fe 3 2 -? ] O 4 where? is the degree of inversion.
The magnetic material known as "ZnFe" has the formula ZnFe 2 O 4 , with Fe 3 occupying the octahedral site and Zn 2 occupies the tetrahedral site, this is an example of a normal spinel ferrite structure.
Some ferrites adopt hexagonal crystal structures, such as barium and ferrite strontium BaFe 12 O 19 (BaO: 6Fe 2 O 3 ) and SrFe 12 O 19 (SrO: 6Fe 2 O 3 ).
In terms of their magnetic properties, different ferrites are often classified as "soft", "semi-hard" or "hard", referring to their low or high magnetic coercivity, as follows.
Smooth grains
Ferrites used in transformers or electromagnetic cores contain nickel, zinc, and/or manganese compounds. They have low coercivity and are called soft ferrite . Low coercivity means that the magnetization of the material can easily reverse without losing much energy (hysteresis losses), while high material resistivity prevents eddy currents in the core, another source of energy loss. Because of their relatively low losses at high frequencies, they are widely used in transformer and RF core transformers in applications such as switch mode power supply and loopstick antennas used in AM radios.
The most common soft ferrite is:
- Manganese-zinc ferrite , with the formula Mn a Zn (1-a) Fe 2 O 4 ). MnZn has higher permeability and induction of saturation than NiZn.
- Nickel-zinc ferrite ( NiZn , with the formula Ni a Zn (1-a) Fe 2 O 4 ). The ferrite NiZn shows a higher resistivity than MnZn, and is therefore more suitable for frequencies above 1 MHz.
For applications under 5 MHz, MnZn ferrite is used; on top of that, NiZn is the usual choice. The exception is the common mode inductor, where the preferred threshold is at 70 MHz.
Semitic hard-fist
- Cobalt ferrite , CoFe 2 O 4 (CoOÃ, Â · Fe 2 O < sub> 3 ), are among the soft and hard magnetic materials and are usually classified as semi-hard materials. It is mainly used for magnetostrictive applications such as sensors and actuators thanks to its high saturation magnetostriction (~ 200 ppm). CoFe 2 O 4 also has the benefit of being rare-earth free, which makes it a good substitute for Terfenol-D. In addition, magnetostrictive properties can be tuned by pushing magnetic uniaxial anisotropy. This can be done with magnetic annealing, magnetic field assisted compaction, or reaction under uniaxial pressure. This last solution has the advantage of being very fast (20 minutes) thanks to the use of spark plasma sintering. The magnetic anisotropy induced in the cobalt ferrite is also useful for enhancing the magnetoelectric effect in the composite.
Fierce hardness
In contrast, a permanent ferrite magnet is made of hard ferrite , which has high coercivity and high remanence after magnetization. Iron oxide and barium or strontium carbonate are used in the manufacture of hard ferrite magnets. High coercivity means that materials are very resistant to magnetic damage, essential characteristics for permanent magnets. They also have high magnetic permeability. It's called cheap ceramic magnet , and is widely used in household products like refrigerator magnets. The maximum magnetic field B is about 0.35 tesla and the magnetic field strength H is about 30 to 160 kiloampere rounds per meter (400 to 2,000 oersteds). The density of ferrite magnets is about 5 g/cm 3 .
The most common hard ferrites are:
- Strontium ferrite , SrFe 12 O 19 (SrOÃ, 6Fe 2 O 3 ), used in small electric motors, microwave devices, recording media, magneto-optical media, telecommunications, and electronics industries.
- Barium ferrite , BaFe 12 O 19 (BaOÃ, 6Fe 2 O 3 ), common materials for permanent magnet applications. Barium ferrite is a strong ceramic that is generally stable against moisture and corrosion resistance. They are used in eg. magnetic loudspeaker and as a medium for magnetic recording, eg. on a magnetic stripe card.
Maps Ferrite (magnet)
Production
Ferrites are produced by heating the oxide mixture of the constituent metals at high temperatures, as shown in this ideal equation:
- Fe 2 O 3 ZnO -> ZnFe 2 O 4
In some cases, the fine-powder precursor mixture is pressed into the mold. For barium and strontium ferrites, these metals are usually supplied as carbonates, BaCO 3 or SrCO 3 . During the heating process, the carbonate is calcined:
- MCO 3 -> MO CO 2
After this decarboxylation stage, the two oxides combine to give the ferrite. The resulting oxide mixture is sintered.
Processing
After obtaining the ferrite, the cooled product is milled into particles smaller than 2 Ã,Âμm, small enough that each particle consists of one magnetic domain. The powder is then pressed into shape, dried, and sintered again. The formation can be done in an external magnetic field, to achieve the preferred particle orientation (anisotropy).
Small and geometric shapes can easily be produced by dry pressing. However, in such a process, small particles can agglomerate and produce less severe magnetic properties than wet pressing. Direct calcination and sintering without re-grinding may also but lead to poor magnetic properties.
Electromagnets are also sintered (pre-reacted), milled and pressed. However, sintering takes place in certain atmospheres, for example one with a lack of oxygen. The chemical composition and in particular the structure vary greatly between precursors and sintered products.
To allow efficient buildup of products in the furnace during sintering and prevent components from sticking together, many manufacturers separate the warehouse using ceramic powder separator sheet. These sheets are available in various materials such as alumina, zirconia and magnesia. They are also available in fine, medium and rough particle sizes. By matching materials and particle size to sintered warehouses, surface damage and contamination can be reduced while maximizing furnace loading.
Usage
The ferrite core is used in electronic inductors, transformers, and electromagnets where high electrical resistance of ferrite causes very low eddy current losses. They are commonly seen as bumps in computer cables, called ferrite beads, which help prevent high-frequency electrical interference (radio frequency interference) from exiting or entering equipment.
Initial computer memory is stored data in the remaining magnetic field of the hard ferrite core, which is assembled into an array of core memory . The ferrite powder is used in the magnetic recording tape layer. One such type of material is iron (III) oxide.
Ferrite particles are also used as components of radar or coating absorbents used in stealth aircraft and in absorbing tiles lining the space used for measurement of electromagnetic compatibility.
The most common audio magnets, including those used in loudspeakers, are ferrite magnets. The ferrite magnet has replaced many of Alnico's magnets in this app.
It is a common magnetic material for pickup of electromagnetic instruments.
The ferrite nanoparticles exhibit superparamagnetic properties.
History
Yogoro Kato and Takeshi Takei from Tokyo Institute of Technology synthesized the first ferrite compound in 1930. This led to the establishment of TDK Corporation in 1935, to produce the material.
Barium hexaferrite (BaFe 12 O 19 ) was discovered in 1950 at Philips Natuurkundig Laboratory ( Philips Physics Laboratory ). The discovery was somewhat unintentional - by mistake by an assistant who was supposed to prepare a hexison lanthanum ferrite sample for a team investigating its use as a semiconductor material. When it discovered that it was truly a magnetic material, and confirmed its structure by X-ray crystallography, they forwarded it to a magnetic research group. Barium hexaferrite has high coercivity (170 kA/m) and low raw material cost. It was developed as a product by Philips Industries (The Netherlands) and from 1952 marketed under the trade name Ferroxdure . Low prices and good performance lead to a rapid increase in the use of permanent magnets.
In 1960 Philips developed strontium hexaferrite (SrFe 12 O 19 ), with better properties than barium hexaferrite. Barium and strontium hexaferrite dominate the market because of its low cost. Yet other materials have been found with better properties. BaFe 2 2 Fe 3 16 O 27 came in 1980. and Ba 2 ZnFe 18 O 23 came in 1991.
See also
- The properties of ferromagnetic materials
- The ferrite core
References
External links
- International Magnet Association
- What is the bulge at the end of the computer cable?
Source
- MMPA 0100-00, Standard Specification for Permanent Magnetic Materials
- Meeldijk, Victor Electronic Components: Elections and Applications Guide , 1997 Wiley ISBNÃ, 0-471-18972-3
- Ott, Henry Noise Reduction Techniques in Electronic Systems 1988 Wiley ISBNÃ, 0-471-85068-3
- Luecke, Gerald and others General Plus Plus Radar Endorsement Operator License 2004, Master Pub. ISBNÃ, 0-945053-14-2
- Bartlett, Bruce, and others Practical Recording Techniques 2005 Focal Press ISBNÃ, 0-240-80685-9
- Schaller, George E. Ferris & amp; Effect on Material Performance
Source of the article : Wikipedia
0 Comments