The magnet consists of iron, cobalt, nickel, etcatomThe internal structure of its atoms is special, and it has magnetic moments.Magnets can producemagnetic field, attractiveFerromagnetismSubstance such asiron、nickel、cobaltAnd other metals.
Type of magnet: shape magnet: square magnet, tile magnet, special-shaped magnet, cylindrical magnet, circular magnet, circular magnet, magnetic rod magnet, magnetic frame magnet, attribute magnet: samarium cobalt magnet, neodymium iron boron magnet (powerful magnet)ferrite magnet 、Alnico magnetFerrochrome cobalt magnets, industrial magnets: magnetic components, motor magnets, rubber magnets, plastic magnets, etc.Magnet minutePermanent magnetWith soft magnets and permanent magnets, strong magnets are added to make the spin of magnetic materials and the angular momentum of electrons form a fixed direction,Soft magnetismPower on.(It is also a method of adding magnetic force) The soft iron will slowly lose its magnetism when it is removed by the current.
Hang the midpoint of the bar magnet with a thin line. When it is stationary, its two ends will point to the south and north of the earth respectively. The end pointing to the north is calledRefers to the North PoleorN-pole, the end pointing south isGuide poleorS-pole。
If we think of the earth as a big magnet, thenmagnetic north Means the South Pole,Geomagnetic south poleIt refers to the North Pole.Between magnets, the same name magnetic pole repels and the different name magnetic pole attracts.Therefore, the compass repels the South Pole, the North Pole repels the North Pole, and the compass attracts the North Pole.
Classification: Magnets can be divided into“Permanent magnet”And“Non permanent magnet”。Permanent magnets can be natural products, also known asNatural magnet, can also be manufactured manually.Non permanent magnets, such aselectromagnet, magnetism only appears under certain conditions.
Magnet is not invented by man, it is naturalmagnetite。ancient GreekPeople and Chinese people found a kind of naturally magnetized stone in nature, called“lodestone”。This kind of stone can magically suck up small pieces of iron, and always points in the same direction after swinging at will.Early navigators regarded this magnet as their earliestcompassIdentify directions at sea.It should be the Chinese who first discovered and used magnets, that is, to make "compass" with magnetsFour Great Inventions of Chinaone of.
After thousands of years of development, today magnets have become powerful materials in our lives.By synthesizing alloys of different materials, the same effect can be achieved as that of magnetite, and the magnetic force can also be improved.Man made magnets appeared in the 18th century, but they are more powerfulmagnetic material However, the process ofAluminium nickel cobalt（Alnico）。Then, in the 1950sFerrite（Ferrite), who manufactured rare earth magnets [Rare Earth magnet, including NdFeB and SmCo] in the 1970s.So far,magnetismWith the rapid development of science and technology, strong magnetic materials have also made components smaller.
development
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1822, French physicistArago andLussac It is found that when the current passes through the winding with iron block, it can make the iron block in the winding magnetic
magnet
Change.This is actually the first discovery of the principle of electromagnet.In 1823, Sturgeon also made a similar experiment: he wound 18 rounds of bare copper wire on a U-shaped iron bar that was not a magnet bar. When the copper wire was connected to the voltaic battery, the copper wire coil wound on the U-shaped iron bar produced a dense magnetic field, which turned the U-shaped iron bar into an "electromagnet".The magnetic energy on this kind of electromagnet is magnified many times than the permanent magnetic energy. It can pick up iron blocks 20 times heavier than it. When the power is cut off, the U-shaped iron bar can't hold any iron blocks and becomes an ordinary iron bar again.Sturgeon's invention of electromagnet made people seeelectric energyThe bright prospect of transforming into magnetic energy soon spread in Britain, the United States and some coastal countries in Western Europe.In 1829, Henry, an American electrician, made some innovations to the Sturgeon electromagnet device. The insulated wire replaced the bare copper wire, so there was no need to worry about being too close to the copper wire and short circuiting.Because the wires have an insulating layer, they can be tightly wound round and round. The denser the coils are, the stronger the magnetic field is generated, which greatly improves the ability to convert electric energy into magnetic energy.In 1831, Henry trial produced a new electromagnet. Although its size was not large, it could lift a ton of iron.The invention of electromagnet has also greatly improved the power of the generator.
development history
It was discovered 5000 years agoNatural magnet（Fe3O4）。
2300 years ago, the Chinese people ground the natural magnet into a spoon shape and put it on a smooth surface“si'nan”This is the first guider in the world.
1000 years ago, Chinese people used magnets to rub iron needlesmagnetization, making the world's first compass.
Around 1100, China combined the magnetic needle and the azimuth plate into a magnetic guider for navigation.
From 1405 to 1432, Zheng He began the great pioneering work of navigation in human history with a guidebook.
1488-1521ColumbusGamma and Magellan used the compass to make world-famous navigational discoveries.
In 1600, William Gibb, an Englishman, published his monograph "Magnet" on magnetism, which developed the understanding and experiments on magnetism of Thales, Aristotle and other predecessors in ancient Greece.
In 1785, French physicist C. Coulomb established the "Coulomb Law" to describe the force between the charge and the magnetic pole with the torsion balance.
1820 Danish physicist HC.OsterIt is found that current induces magnetic force.
1873 British physicist JC.maxwellIn his monograph "On electricity and magnetism", he completed the unified electromagnetic theory.
1898-1899 French physicist P. Curie found that ferromagnetic materials becameParamagnetismPhenomenon.
1905 French physicist P1. Lang Zhiwan explained the change of paramagnetism with temperature based on the theory of statistical mechanics.
In 1907, French physicist PE. Weiss proposedMolecular field theory, which extends Lang Zhiwan's theory.
In 1921, Austrian physicist W. Pauli proposed the Bohr magneton as the basic unit of atomic magnetic moment.American physicist A. Compton proposed that electrons also have magnetic moments corresponding to spin.
In 1928, British physicist PA. M. Dirac perfectly explained the intrinsic spin and magnetic moment of the electron with relativistic quantum mechanics.Together with the German physicist W. Heisenberg, he proved the existence of the exchange force of electrostatic origin, which laid the foundation of modern magnetism.
In 1936, Lang Dao, a Soviet physicist, completed the great book "Theoretical Physics Course", which contains a comprehensive and wonderful chapter on modern electromagnetism and ferromagnetism.
In 1936-1948, French physicist L. Nair put forward the concept and theory of antiferromagnetism and ferromagnetism, and deepened the understanding of material magnetism in subsequent years of research.
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Travel to America in 1967AustriaPhysicist KJ. Under the guidance of quantum magnetism, Snyder found thatRare earth magnet（SmCo5），Thus, a new chapter in the development of permanent magnetic materials is opened.
In 1967, Strut et al. of Dayton University in the United States developedSamarium cobalt magnet, marking the arrival of the era of rare earth magnets.
1982 Japansumitomo Invented by Masato Sagawa, a special metalNdFeB Magnet, the third generation of rare-earth permanent magnet - Nd2Fe14B came out.
In 1990, the atomic gap magnet Sm-Fe-N came out.
1991 German physicist EF. Keneller put forward the theoretical basis of the exchange effect of two-phase composite magnets, and pointed out the development prospect of nanocrystalline magnets.
With the development of society, the application of magnets is more and more extensive, from high-tech products to the simplest packaging magnets.
From the perspective of the development history of magnets, carbon steel, tungsten steel, chromium steel and cobalt steel were mainly used as permanent magnetic materials at the end of the 19th century and the beginning of the 20th century.
the thirties
In the late 1930s,Alnico magnetSuccessful development makes the large-scale application of magnets possible.
The Fifties
In the 1950s, the emergence of barium ferrite magnets not only reduced the cost of permanent magnets, but also expanded the application range of permanent magnet materials to the high-frequency field.
1960s
By the 1960s, the emergence of samarium cobalt permanent magnets opened a new era for the application of magnets.So far, rare earth permanent magnets have experienced the first generation of SmCofive, the second generation precipitation hardening SmtwoCoseventeenIt has developed into the third generation Nd-Fe-B permanent magnetic material.At present, ferrite magnets are still the most used permanent magnetic materials, but the output value of Nd-Fe-B magnets has greatly exceeded that of ferrite permanent magnetic materials, and the production of Nd-Fe-B magnets has developed into a major industry.
Discovery of magnetic phenomena
In the Warring States Period, our ancestors have accumulated a lot of knowledge in this regard, and they often met when exploring iron oremagnetite, that is, magnetite (mainly composed ofFerric tetroxide）。These findings have been recorded long ago.These discoveries were first recorded in several articles of Guanzi: "If there is a magnet on the mountain, there is gold and copper under it."
Documentation
Other ancient books such as《shanhaiching》There are similar records in.The iron absorption property of magnet has been discovered for a long time《Lu's Spring and Autumn Period》In the nine volumes of Mastery, there is a saying: "Mercy attracts iron, or it may be cited." At that time, people called "magnetism" "kindness". They regarded the magnet attracting iron as a kind mother's attraction to their children.And he thought: "Stone is the mother of iron, but there are two kinds of stone: kind and unkind. The kind stone can attract his children, but the unkind stone cannot." Before the Han Dynasty, people wrote the magnet as "kind stone", which means kind stone.
Three hundred and twenty miles to the north, it is called Guanti Mountain. There are many Chuzhe trees on the mountain, and quicksand and rocks on the bottom.There is no animal. Its shape is like an ox with white tail, and its sound is like a turtle. It is called Na Fu.There is a bird. It looks like a female pheasant, but people's faces. When people see it, they leap. It's called Tuosi, and it calls itself.The water of Han, the craftsman, is out of the way, while the water flows to the west in Xuanze, where there are many magnets.
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③ Magnet: also used“Cishi”, a natural ore with the property of attracting iron, nickel, cobalt and other metal substances.Commonly known as magnetite, it is now called magnetite.The compass, one of the four great inventions in ancient China, was made of magnetite.
(Shan Hai Jing Bei Shan Jing)
attempt
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Since magnets can attract iron, can they also attract other metals?Our ancestors made many attempts and found that magnets could not attract gold, silver, copper and other metals, nor bricks and tiles.In the Western Han Dynasty, people realized that magnets could only attract iron, but not other objects.When two magnets are put together and close to each other, sometimes they attract each other and sometimes they repel each other.It is known that a magnet has two poles, one is called N pole and the other is called S pole.Homosexual poles repel each other, while opposite poles attract each other.At that time, people did not know this truth, but they were able to detect this phenomenon.
In the Western Han Dynasty, there was a man namedLuan DaHe used the nature of the magnet to make something like two chessmen. By adjusting the mutual position of the polarity of the two chessmen, sometimes the two chessmen attract each other, sometimes repel each other.Luan Da called it“Fight chess”。He dedicated this novel gadget to Emperor Wu of the Han Dynasty and demonstrated it on the spot.Emperor Wu of the Han Dynasty was so surprised that his heart was so happy that he made Luan a "general with five benefits".Luan Da used the nature of the magnet to make novel gadgets to deceive Emperor Wu of the Han Dynasty.
The earth is also a big magnet. Its two poles are near the geographical south pole and geographical north pole respectively.So the magnets on the earth's surface can be freeturnWhen the magnets are same, they repel each other, while the opposite magnets attract each other, indicating north and south.The ancients did not understand this truth, but they were very clear about this kind of phenomenon.
classification
Magnets can be divided into "permanent magnets" and "non permanent magnets".Permanent magnets can be natural products, also known asNatural magnet, or it can be manufactured manually (the strongest magnet is neodymium magnet).It is not a permanent magnet. It can be magnetic only under certain conditions. UsuallyelectromagnetIn other words, current is used to strengthen its magnetic field.
definition
Magnet, should be calledMagnetic steelMagnet, magnetic steel is mainly divided into two categories: soft magnetic and hard magnetic.
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The soft magnet comprises a silicon steel sheet and a soft magnet core;Hard magnets include aluminum nickel cobalt, samarium cobalt, ferrite and neodymium iron boron. Among them, the most expensive is samarium cobalt magnetic steel, the cheapest is ferrite magnetic steel, and the highest performance is neodymium iron boron magnetic steel, but the most stable performance and temperaturecoefficientThe best one is aluminum nickel cobalt magnetic steel. Users can choose different hard magnetic products according to different needs.
The magnet we say generally refers to permanent magnet.
Permanent magnet can be divided into two categories.
First category
Metal alloy magnets includeNeodymium iron boron magnet（NdtwoFefourteenB magnet）、Samarium cobalt magnet（SmCo magnet）、Alnico magnet(ALNiCO magnet) FeCrCo magnet
Sintered rubidium iron boron: it is a new type of permanent magnet material developed after 1983. It has extremely high magnetic properties and is widely used in various permanent magnet motors, engineering machinery, electroacoustics, electrical appliances and medical devices.
Sintered samarium cobalt permanent magnet is an excellent permanent magnet material, which has high magnetic measurement performance, strong corrosion resistance, oxidation resistance, low temperature coefficient, high Curie temperature, and can be used in higher environments. It is widely used in motors, sensors, detectors, radars, and other high-tech fields.
Al Ni Co is suitable for complex shapes.Light, thin and small products are widely used in instruments, communications, magnetoelectric switches and various sensors.
Ferrochrome cobalt magnet
FeCrCo magnetIt is the transformer of permanent magnet, and the alloy permanent magnet is the most deformable. It can be used for wire drawing (0.2-0.3mm), tube drawing, strip rolling and various machining.A. FeCrCoDeformed permanent magnet alloyIt has high magnetism, comparable to AlNiCo permanent magnet alloy, but its Co content is about 50% lower than AlNiCo.B. FeCrCo alloy has excellent plasticity and ductility, which is easy to processPermanent magnet alloyIt has incomparable characteristics, and the high service temperature of this alloy is about 400, which is beyond the reach of NdFeB rare earth permanent magnet.C. FeCrCo alloy can be processed into wires, rods, tubes, belts and forgings. After turning, milling, planing, drilling, stamping and other mechanical processing, it can be made into permanent magnetic components with complex shapes, especially for small, long and thin components.The thinnest strip can reach 0.05mm, and the thinnest wire can be processed to 0.1mm.
Positive and negative poles of magnet
Second category
Ferrite
1．Neodymium iron boron magnetIt is the magnet with the highest commercialized performance found at present and is called Magnet King. It has extremely high magnetic properties and its maximum magnetic energy product (BHmax) is more than 10 times higher than that of ferrite.Its own machining performance is also quite good.The operating temperature can be up to 200 ℃.Moreover, it is hard, stable and cost-effective, so it is widely used.But because itChemical activityIt is very strong, so its surface must be coated.(e.g. Zn, Ni plating,electrophoresis、passivationEtc.).
2．ferrite magnet Its main raw materials include BaFetwelveOnineteenAnd SrFetwelveOnineteen。It is made by ceramic technology. It is hard and belongs toBrittle materialFerrite magnets have become the most widely usedPermanent magnet。
3．Alnico magnetIt is composed of aluminum, nickel, cobalt, iron and othersTrace metal elementsAn alloy formed.The casting process can be processed into different sizes and shapes with good workability.The cast Al Ni Co permanent magnet has the lowest reversible temperature coefficient, and the operating temperature can reach more than 600 ℃.Al Ni Co permanent magnetic products are widely used in various instruments and other applications.
4. SmCo is divided into SmCo according to different compositionsfiveAnd SmtwoCoseventeen。Its development is limited due to the high price of its materials.SmCo asRare earth permanent magnetIron not only has high magnetic energy product (14-28MGOe), reliable coercivity and good temperature characteristics.AndNeodymium iron boron magnetIn contrast, SmCo magnets are more suitable for working at high temperatures.
permanent magnet
Permanent magnets can be natural products, also known as naturalMagnetite, can also be manufactured manually (the strongest magnet isNdFeB Magnet).
The non permanent magnet will suddenly lose its magnetism when heated to a certain temperature, which is due to the many "elements" that make up the magnetmagnet”Caused by the arrangement from order to disorder;A magnet that loses its magnetism is put into the magnetic field whenMagnetizationWhen it reaches a certain value, it ismagnetizationThe arrangement of "meta magnets" is from disorder to order.
Artificial magnet
Artificial magnet: divided intoHoof magnetandBar magnet, is the most common in our life, and the hoof magnet is more popular.A single-sided magnet refers to a magnet with one side magnetic and the other side weak magnetic. The method is to wrap one side of the double-sided magnet with a specially treated galvanized iron sheet, so that the magnetism of the wrapped side will be shielded, the magnetic force will be refracted to the other side, and the magnetism of the other side will be enhanced.In some cases, only one side needs to be magnetic, and the other side will cause damage or interference if it is magnetic;On some occasions, such as the magnet on the packaging box, only one side of the magnet needs to be magnetic, and the other side is optional. It is useless to have magnetism. In this way, the use of single-sided magnets will greatly reduce costs and save moneymagnetic material 。The magnetic refraction of a single-sided magnet is like the refraction of a satellite cooker to a signal or the refraction of a flashlight cooker to light
1. Materials: the selection and thickness of materials, as well as the spacing between magnets and materials, are closely related.Pure iron sheet is easy to leak magnetic field, and its refraction will be enhanced after special treatment. However, 100% shielding material has not been developed yet, but the material effects made by different manufacturers are also different.
2. Angle: according to the refraction principle, the arc material has the best effect, and the right angle material has large refraction loss.
3. Space: The magnetic line of force in the air is like a mobile phone signal, which needs space to be refracted.If the flashlight pot is completely wrapped on the lamp, the use effect must be bad, because a lot of light refraction is lost.
How to make the best use of the above principles to enhance the effect of magnetism is the problem of finding the best among many parameters. Many manufacturers are also doing experiments repeatedly. For example, the ideal result of single-sided magnetic treatment of Xi'an Guotai Magnet Factory is to increase 50%, which will greatly reduce production costs and save money in the field of packaging, boxes and bagsmagnetic material 。
Neodymium magnet isSumitomo Special MetalCorporateSagawa ImmortalIt was invented by et al. in 1982. According to its chemical formula, it is mainly composed ofneodymium、ironAndboronAnd other chemical elements.In many fields, it is possible to replace the traditional pure iron magnets, aluminum nickel cobalt alloys and samarium cobalt magnets, such as motors, instruments and meters, automobile industry, petrochemical industry and magnetic medical care products.It can produce various shapes of magnets, such as disk magnets, ring magnets, rectangular magnets, arc magnets and other shapes of magnets.
Strongly magneticNeodymium magnetIt is widely used in electronic products, such as hard disks, mobile phones, headphones, and so on.
Main components
Magnet, also known as magnet, refers to the existence around and inside itselfmagnetic fieldThe objects or materials of are divided into two categories: natural and artificial.Artificial magnets are usually made of metal alloys and have strong magnetism.It can also be divided into "permanent magnet" and "non permanent magnet", namely "hard magnet" and "soft magnet".Main ingredients of natural magnet: ferric oxide,chemical formulaFethreeOfour, often called“Magnetic iron oxide”。Black crystals with magnetic properties.It can be regarded asFerrous oxideAnd ferric oxide.Because inFerric tetroxideThere are two ions with different valence states in the crystal of2+Two thirds are Fe3+, is a complex compound.It is insoluble in water and cannot react with water.It reacts with acid and is insoluble in alkali.It is mainly used for making primer and finish paint, and for electronic industrymagnetic material It is also used as an anti rust agent in the construction industry.
There are mainly three performance parameters to determine the performance of the magnet:
Remnant Br: after the permanent magnet is magnetized to technical saturation and the external magnetic field is removed, the retained Br is called residualMagnetic induction。
Magnetic energy productBH: represents that the magnet is in the air gap space (two magnetsmagnetic poleSpace), namely the magnetostatic energy per unit volume of the air gap.Since this energy is equal to the product of Bm and Hm of the magnet, it is called the magnetic energy product.
magnetic field: The space producing magnetic effect on the magnetic pole is the magnetic field.
Diamagnetism is a kind of material that will produce weak magnetic field when it is in an external magnetic fieldrepulsionA magnetic phenomenon of.
Paramagnetism
Paramagnetism refers to the magnetic state of a material.Some materials can be affected by the external magnetic field, resulting in in-phasemagnetization vector Properties of.Such a substance has positiveMagnetic susceptibility。AndParamagnetismThe opposite phenomenon is calledDiamagnetism。
Ferromagnetism
Ferromagnetism refers to the magnetic state of a material, which is spontaneousmagnetizationPhenomenon.In each materialironIt is the most widely known, hence its name.
Some materials are externalmagnetic fieldAfter being magnetized under the action of, even if the external magnetic field disappears, it can still maintain its magnetized state and become magnetic, which is the so-called spontaneous magnetization phenomenon.be-allPermanent magnetAre ferromagnetic orFerromagnetism。
Basically, the concept of ferromagnetism includes any material that shows magnetism when there is no external magnetic field.Some people still use this concept.But through a deeper understanding of different magnetic substances and their magnetism, scholars have made a more precise definition of this concept.PhysicalProtocellAll magnetic ions in are ferromagnetic only when they point in its magnetic direction.If only part of the ion's magnetic field points to its magnetic direction, it is called ferromagnetism.If the directions of their magnetic ions exactly cancel each other (although all magnetic ions only point to two opposite directions), it is calledAntiferromagnetism。
There is a critical temperature at which the magnetic phenomenon of matter can occur.For ferromagnetic and ferromagnetic materials, this temperature is calledCurie temperature; For antiferromagnetic materials, this temperature is calledNeel temperature 。
Some people think that the attraction between magnets and ferromagnetic materials is the earliest human understanding of magnetism.
Select magnet
Magnet
Before deciding which kind of magnet to choose, you should know what role the magnet is required to play?Main functions: moving objects, fixing objects or lifting objects.
The shape of the magnet required: disc, ring, square, tile or special shape.
Required magnet size: length, width, height, diameter and tolerance, etc.
The attraction of required magnets, expected price and quantity, etc.
compassIt was invented according to the nature of the magnet.
The magnet tastes salty and flat;Returning to liver and kidney meridians;Key quality reduction
It has the effects of calming the liver and suppressing yang, hearing and eyesight, calming nerves, absorbing qi and relieving asthma
It is mainly used to treat liver yang vertigo, panic insomnia, blurred eyes,Tinnitus and deafness, kidney deficiency, asthma and adverse reactions.
Manufacturing of magnets
Some substances can be rubbed into magnets, either iron or steel, but not allSteel CapitalThey can be made into magnets because they contain substances, and stainless steel cannot act as magnets.
Let's make magnets. Magnets and a screwdriver are the materials you need. Use magnets to rub the metal part of the screwdriver. They rub repeatedly from one end to the other to make a magnetic screwdriver.
Orientation direction
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majoritymagnetic material Can be in the same directionMagnetizationTo saturation, this direction is called "magnetization direction" (orientation direction).Magnets without orientation direction (also called isotropic magnets) are better than oriented magnets (also calledanisotropyMagnet) is much weaker.
Definition of North and South Poles of Magnet
The definition of "North Pole" is that after the magnet rotates at will, its north pole points to the north pole of the earth, which is called "N" for short.Similarly, the south pole of the magnet also points to the south pole of the earth, which is called "S" for short.The geomagnetic poles do not coincide with the geographical poles, and there is a certain magnetic declination.
Safely handle magnets
magnet
Always be very careful because the magnets will stick together on their own and may pinch your fingers.Magnets may also be damaged by collision when they are adsorbed to each other (knocking off corners or cracking).
Keep the magnet away from objects that are easy to be magnetized, such asFloppy diskCredit cardgraphoscope, watches, mobile phones, medical devices, etc.
Magnets should be kept away from cardiac pacemakers.For larger magnets, plastic or hard paper gaskets shall be added between each piece to ensure that the magnets can be easily separated.
The magnet should be stored in a dry and constant temperature environment as far as possible.[1]
Magnetic isolation
Only the material that can be adsorbed on the magnet can play the role of isolating the magnetic field, and the thicker the material, the better the effect of magnetic isolation.
Strongest magnet
At present, rare-earth magnets have the highest performance, and neodymium iron boron is the most powerful among rare-earth magnets.However, SmCo is the most powerful magnet in the environment above 200 ℃.
Determine magnetic force
The reason why a magnet has magnetic force is that because the earth rotates, its magnetic field and current will continue to combine strongly, and finally the whole earth will become a large magnetic field.Minerals on the earth such as nickel, cobalt, iron and other substances rotate because of the earth's rotation, thus becoming natural magnets.
Everyone knows that there is a gravitational field between matter.Similar to the magnetic field, it is a field that fills the space around the magnetic pole.The size of the magnetic field can be expressed by the number of imaginary magnetic lines of force. The denser the magnetic lines of force are, the stronger the magnetic field is. On the contrary, the weaker the magnetic field is where the magnetic lines of force are sparse.[2]
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Is there a 100% perfect spherical magnet in the material world?If yes, where is the NS pole of the spherical magnet?If NS is the two ends of its diameter, but the sphere has countless diameters, why are the two ends of other diameters not NS poles?
application
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Application in traditional industry
electromagnet
Onmagnetic material Magnetic sourceelectromagnetic inductionIn magnetic devices, we have mentioned the practical application of some magnetic materials.In fact, magnetic materials have been widely used in various aspects of traditional industry.
For example, if there is no magnetic material, electrification is impossible, because generators are used for power generation, transformers are used for power transmission, motors are used for electric machinery, telephones, radios and televisions use loudspeakers.Many instruments and meters use magnetic steel coil structure.These have already been mentioned in other contents.
Application of Magnet in Medicine
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Carrier pigeon lovers know that if pigeons are released hundreds of kilometers away, they will return home automatically.Why do pigeons have such good ability to recognize their families?It turns out that pigeons are very sensitive to the earth's magnetic field, and they can useGeomagnetic fieldChange to find your own home.If a magnet is tied to the pigeon's head, the pigeon will get lost.If pigeons fly over the radio tower, powerfulelectromagnetic waveDisturbance can also make them lose their way.In medicine, MRI can be used to diagnose abnormal human tissues and determine diseases, which is familiar to usMagnetic resonance imagingThe basic principles of technology are as follows:NucleusIt is positively charged and spins.In general, the arrangement of nuclear spin axis is irregular, but when it is placed in an external magnetic field, the nuclear spin spatial orientation transitions from disorder to order.The magnetization vector of the spin system increases gradually from zero when the system reachesbalanceWhen, the magnetization reaches a stable value.If the nuclear spin system is affected by external forces, such asradio frequencyThe resonance effect can be caused by exciting the atomic nucleus.After the RF pulse stops, the atomic nucleus that has been stimulated in the spin system cannot maintain this state, and will return to the original arrangement state in the magnetic field, while releasing weak energy, which becomes a radio signal. Detect many signals and make spatial resolution at the time to get the distribution image of atomic nuclei in motion.The characteristic of NMR is that the flowing liquid does not produce signals, which is called flow effect or flow blank effect.Therefore, the blood vessels are grayish white tubular structures, while the blood is black without signal.This makes it easy for the blood vessels to separate from the soft tissue.The normal spinal cord is surrounded by cerebrospinal fluid, which is black, and white dura is set off by fat, so that the spinal cord shows a white strong signal structure.Magnetic resonance imaging has been applied to the imaging diagnosis of various systems of the whole body.The best effect is the brain, its spinal cord, heart and large vessels, joint bones, soft tissue and pelvic cavity.yesCardiovascular diseaseIt can not only observe the anatomical changes of each chamber, large blood vessel and valve, but also make ventricular analysis, carry out qualitative and semi quantitative diagnosis, and make multiple sectional images with high spatial resolution, showing the whole picture of heart and disease, and its relationship with surrounding structures, which is superior to other X-ray imagingtwo-dimensionalUltrasoundnuclideAnd CT examination.Magnetism can not only diagnose, but also help treat diseases.MagnetiteIt is a traditional Chinese medicine.People use the magnetic difference of different components in blood to separate red blood cells and white blood cells.In addition, the interaction between magnetic field and human meridians can achieve magnetic therapy, which has unique effects in treating a variety of diseases. There are already applications such as magnetic therapy pillow and magnetic therapy belt.The iron remover made of magnets can remove iron particles that may exist in flour, etc. Magnetized water can prevent boiler scaling, and magnetized seeds can increase crop production to a certain extent.[3]
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Magnetic applications in astronomy and other fields
We already know that the earth is a huge magnet. What is the relationship between it and geological conditions?What about the magnetic field in the universe?
At least in the picture, we have all seen the brilliant northern lights.The Northern Lights have been recorded in China since ancient times.The Northern Lights are actually particles andgeomagnetic fieldResults of interaction.solar windIs the high energy emitted by the sunCharged particle flow。When they arriveEarth time, interacts with the geomagnetic field, just like the current carrying wire is forced in the magnetic field, making these particles move and gather toward the South and North Pole, and collide with the rarefied gas in the upper air of the earth, resulting in the gas molecules being excited, thus emitting light.
Sunspots are regions on the sun where the magnetic field is very active.The eruption of sunspots will have an impact on our life, such as temporarily interrupting radio communication.Therefore, the study of sunspots is of great significance to us.
The change of geomagnetism can be used to explore mineral deposits.Since all materials have strong or weak magnetism, if they are gathered together to form a deposit, they will inevitably interfere with the geomagnetic field in the nearby area, making the geomagnetic field abnormal.According to this, we can measure the magnetism of the earth on land, at sea or in the air, obtain the geomagnetic map, analyze and further explore the areas with magnetic anomalies on the geomagnetic map, and often find unknown mineral deposits or special geological structures.
Rocks of different geological ages often have different magnetic properties.Therefore, the change of geological age and crustal movement can be judged according to the magnetism of rocks.
Many mineral resources are symbiotic, that is to say, several minerals are mixed together, and they have different magnetic properties.Using this feature, people have developedMagnetic separatorBy using the different magnetism of minerals with different components and the difference in magnetic strength, these substances are attracted by magnets, so their attraction is different. As a result, minerals with different magnetic properties mixed together can be separated to achieve magnetic beneficiation.
Magnetic Applications in Military Field
magnetic material It is also widely used in the military field.For example, ordinary mines or mines can only explode when they touch the target, so their effects are limited.If a magnetic sensor is installed on a mine or mine, since tanks or warships are made of steel, when they approach (without touching the target), the sensor can detect the change of magnetic field, which makes the mine or mine explode, improving the lethality.
In modern war, air control is one of the keys to win the battle.However, the aircraft is easy to be detected by the enemy's radar during flight, so it is dangerous.In order to avoid the monitoring of the enemy radar, a special layer ofmagnetic material ——Wave absorbing materialIt can absorb the electromagnetic wave emitted by the radar, so that only a few electromagnetic waves will be reflected when the radar electromagnetic wave touches the aircraft. Therefore, the enemy radar cannot detect the radar echo and cannot find the aircraft, which makes the aircraft achieve the purpose of stealth.This is the famous "stealth aircraft".Stealth technology is a hot spot in the field of military scientific research in the world.F117 in the United StatesStealth fighterIt is an example of successful application of stealth technology.
In the "Star Wars" program of the United States, there is a new weapon“Electromagnetic weapon”Development and research of.The traditional artillery uses the thrust generated by the instant expansion of ammunition when it explodes to accelerate the projectile rapidly and push it out of the chamber.The electromagnetic gun is to put the shell in the solenoid and energize the solenoid, then the magnetic field generated by the solenoid will have a huge driving force on the shell and launch the shell.This is the so-called electromagnetic gun.SimilarElectromagnetic missileEtc.[4]
Batching → smelting and ingot making → milling → molding → sintering and tempering → magnetic testing → grinding → pin cutting →electroplate→magnetization→ Finished products.Among them, batching is the basis, and sintering tempering is the key production tool of Nd-Fe-B magnets: there are smelting furnace, jaw crusher, ball mill, air flow mill, press molding machinevacuumPackaging machineIsostatic press, sintering furnace, heat treatment vacuum furnace, magnetic property testerGauss meter。[5]
Magnetically Levitated TrainIt is a kind of magnetic suspension high-speed train system that adopts non-contact electromagnetic suspension, guidance and drive system.With a speed of more than 500 kilometers per hour, it is the fastest ground passenger transport in the world today. It has high speed, strong climbing ability and low energy consumptionnoiseSmall, safe and comfortable, no fuel, less pollution, low price and other advantages.In addition, it adopts overhead mode, and occupies very little arable land.Maglev train means that these trains use the basic principle of magnetism to suspend on the guide rail instead of the old steel wheel and rail train.magnetic suspension technique utilizeElectromagnetic forceThe whole train carriage is lifted up to get rid of the annoying friction and unpleasant noise, and realize the fast "flight" without contact with the ground and fuel.
Magnetically Levitated TrainIt is the most fundamental breakthrough in railway technology since Stephenson's "Rocket" steam locomotive came out about 200 years ago.Maglev train seems to be a new thing today, but its theoretical preparation has a long history.The research of magnetic levitation technology originated from Germany. As early as 1922, German engineer Herman Kempel proposed the principle of electromagnetic levitation, and applied for a patent of magnetic levitation train in 1934.Since the 1970s, with the continuous strengthening of the economic strength of the world's industrialized countries, in order to improve the transportation capacity to meet the needs of their economic development, Germany, Japan, the United States, Canada, France, the United Kingdom and other developed countries have begun to plan the development of the maglev transportation system.
ChinaNdFeB The application of magnets is as follows. The application of high-tech products accounts for 37%, such asNuclear magnetic resonance imager（MRI）、Mobile phone vibration, hard disk drive voice coil (VCM), CD (DVDCD-ROM）Drive spindle, electric tool, electric car, engine of variable frequency air conditioner.The application of traditional medium and low-end products accounts for 63%, such as audio devices, magnetic adsorption devicesMagnetic separator、Magnetizer。
electromagnet
definition
With iron core inside and using currentcoilThe device that makes it magnetic like a magnet is called an electromagnet.It is usually made into a strip or hoof shape.The iron core shall be made of soft iron or silicon steel that is easy to magnetize and lose magnetism.Such electromagnet has magnetism when it is powered on, and will disappear after the power is cut off.Electromagnets are widely used in daily life.The invention of electromagnet has also greatly improved the power of the generator.
application
Electromagnets are widely used in daily life.Electromagnet is an application of current magnetic effect (electromagnetism), which is closely related to life, such aselectromagnetic relay 、Electromagnetic crane、Magnetically Levitated TrainEtc.Electromagnets can be divided intoDC electromagnetandalternating currentThere are two types of magnets.If electromagnets are classified according to their purposes, they can be divided into the following five categories: (1) Traction electromagnets are mainly used to pull mechanical devices, open or close various valves, and perform automatic control tasks.（2）Lifting electromagnet——Used as a lifting device to lift steel ingots, steel, iron sand, etcFerromagnetismMaterial Science.(3) Brake electromagnet - mainly used to brake the motor to achieve accurate stop.(4) Electromagnetic system of automatic electrical appliances - such as electromagnetic system of electromagnetic relay and contactor, automatic switchelectromagnetic overload release And operating electromagnet, etc.(5) Electromagnets for other purposes - such as grinding machinesElectromagnetic chuckas well asElectromagnetic vibratorEtc.
principle
When the solenoid is energized, it can produce a magneticmagnetic field。The circle in the figure is the cross section of the wire, the point represents the current flowing out of the screen, and the fork represents the current flowing into the screen;The elliptical circle with an arrow is the magnetic force line.When direct current passes through the conductor, it will generate a magnetic field, while when it passes through the conductor as a solenoid, it will generate a magnetic field similar to a bar magnet.Add a magnetic material in the center of the solenoid, and the magnetic material will be magnetized to strengthen the magnetic field.Generally speaking, the magnetic field strength generated by the electromagnet is related to the size of DC, the number of coils and the magnetic conductive material in the center. When designing the electromagnet, we will pay attention to the distribution of coils and the selection of iron conductive materials, and use the size of DC to control the magnetic field strength.However, the resistance of the coil material limits the size of the magnetic field generated by the electromagnet, but with the discovery and application of superconductors, there will be opportunities to break through the existing limitations.
Electromagnet history
Sturgeon's electromagnet.In 1825, William Sturgeon (1783-1850), an Englishman, wound a metal wire with current on an insulated rod and invented the electromagnet.
Joseph Henry (1797-1878), an American physicist, was able to pick up a ton of iron after he learned the news and wound dense coils on the soft iron core.
make
Simple self-made electromagnet:
It needs enameled wire and iron nail as its body;Battery orPower supplySupply current.
matters needing attention
The paint at the end of the enameled wire shall be scraped off or burned.
The enameled wire shall be wound in the same direction.
The magnetic force of the electromagnet can be changed.
The direction of the electromagnet can be changed.
The electromagnet force can be controlled freely.[6]
Can permanent magnet and steel wire be used to make permanent magnet
Announce
edit
Rumor: Tin foil plus magnets can generate electricity?The guy has built a perpetual motion machine, which can light a big light bulb after starting[7]。
Truth: Perpetual motion machine does not exist[7]。
Apply some unknown mucus on the shiny silver "tin foil", connect the wires, lay a layer of paper, put another piece of tin foil, apply mucus, connect the wires, and roll it up to provide power.This device can drive toy motors, light LED bulbs, and do many other things.There are a lot of similar videos on the Internet now, some just say that "tin foil plus magnets can generate electricity", and some also add a "perpetual motion machine" gimmick.In fact, this is a common "script", or hoax, to increase the number of clicks on videos[7]。
It seems very strange. To put it bluntly, it is worthless: these videos are just chemical batteries.When two different metals are put in a chemical solution, a chemical battery can be formed to convert chemical energy into electrical energy.Commonly used in daily lifeLead acid batteryIt's a chemical battery.In this kind of video, "tin foil" and "wire" are different metals. The coated mucus acts as an electrolyte, and together they form a chemical battery, which can then drive the toy motor and light the LED bulb[7]。
The magnet here may provide a magnetic field to make the coil with current move, or it may be just a device (some toy motors can move when they are powered on).The current required to light the LED is very small, and the current required by the toy motor should also be small.A simple chemical battery is enough. Even if the current is not enough, he can do something about it, such as changing a dry battery (it is easy to do this in the video).For ordinary people, the magic performed on the spot can fool people around. I know it's fake, but it's hard to see where he is playing tricks[7]。
As for the perpetual motion machine, it does not exist - it is a gimmick used to increase the number of clicks.China's nine-year compulsory education and science popularization have made most people know that perpetual motion machine is impossible because it violatesconservation of energy。However, adding the word "perpetual motion machine" to the title is still very attractive[7]。
