Those transcendental inventions

Magnets are not invented by people, but there are natural magnetite. The earliest effective use of magnets should be from China. Therefore, the compass is one of the four great inventions of China people. As for the composition, it is iron, cobalt, nickel and so on. Its atomic structure is very special. The atom itself has a magnetic moment. Generally, these mineral molecules are arranged in disorder. The interaction of magnetic fields does not show magnetism. However, under the guidance of external force (such as magnetic field), the arrangement of molecules tends to be consistent, which is also commonly known as magnets. Iron, cobalt and nickel are the most commonly used magnetic substances. Magnets are basically divided into permanent magnets and soft iron permanent magnets. Adding strong magnetism makes the spin of magnetic substance and the angular momentum of electrons arrange in a fixed direction. Soft magnetism plus current (also a method of adding magnetism). Removing soft iron will gradually lose its magnetism. As for the earliest magnet, who found the oldest record is China Huangdi vs Chiyou's South Locomotive, which is called one of the four great inventions in China! China knew about magnetic polarization in the first century BC. During the Warring States period, a natural magnet was placed on a graduated copper plate for divination. During the Northern Song Dynasty, there were two ways to make artificial magnets. One is to place the red-hot iron needle in the north-south direction, and after rapid cooling, the iron needle is magnetized by the earth's magnetic field. The other is made by rubbing an iron needle with a magnet. Meng Qian Bitan recorded the existence of magnetic declination, and found that under the influence of magnetic declination, the magnetic needle pointed to the south, slightly to the east than the real south. Based on this knowledge, the scientific application of magnets as compasses has been developed. Magnet is just a general term, which refers to something with magnetism. The actual composition does not necessarily contain iron. Pure metallic iron itself has no permanent magnetism, and it will be induced to produce magnetism only when it is close to a permanent magnet. Generally, other impurity elements (such as carbon) are added to the permanent magnet to stabilize the magnetism, but this will reduce the freedom of electrons and make it difficult to conduct electricity, so the light bulb will not light when the current passes. Iron is a common magnetic element, but many other elements are more magnetic, such as rubidium, iron and boron.

[Edit this paragraph] Basic knowledge

The ancient Greeks and China discovered that there was a naturally magnetized stone in nature, called a "magnet". This kind of stone can magically pick up a small piece of iron and swing it at will and always point in the same direction. Early navigators used this magnet as their earliest compass to tell directions at sea.

After thousands of years of development, magnets have become a powerful material in our life today. By synthesizing alloys of different materials, we can achieve the same effect as magnets and improve the magnetic force. /kloc-artificial magnets appeared in the 0/8th century, but the process of making stronger magnetic materials was very slow, and Al-Ni-Co was not produced until the 1920s. Subsequently, ferrite was manufactured in 1950s and [rare earth magnets [including NdFeB and SmCo]] was manufactured in 1970s. At this point, magnetic technology has developed rapidly, and ferromagnetic materials have also made components more miniaturized.

[Edit this paragraph] magnetization (orientation) direction

Most magnetic materials can be magnetized to saturation in the same direction, which is called "magnetization direction" (orientation direction). Non-oriented magnets (also called isotropic magnets) are much weaker than oriented magnets (also called anisotropic magnets).

What is the standard industrial definition of "North and South Pole"?

The definition of "North Pole" is that after a magnet rotates at will, its North Pole points to the North Pole of the Earth. Similarly, the south pole of the magnet also points to the south pole of the earth.

How can you tell the north pole of a magnet without labeling it?

Obviously, eyes alone can't tell the difference. You can use a compass to get close to the magnet, and the pointer pointing to the north pole of the earth will point to the south pole of the magnet.

How to handle and store magnets safely?

Be very careful, because magnets attract each other and may pinch your fingers. When magnets attract each other, they may also be damaged by collision (knocking off corners or cracking).

Keep the magnet away from easily magnetized objects, such as floppy disks, credit cards, computer monitors, watches, mobile phones, medical devices, etc.

Magnets should be kept away from pacemakers.

For larger magnets, plastic or cardboard washers should be added between each magnet to ensure that the magnets can be easily separated.

Magnets should be stored in a dry and constant temperature environment as much as possible.

How to achieve magnetic isolation?

Only the material that can be adsorbed on the magnet can isolate the magnetic field, and the thicker the material, the better the magnetic isolation effect.

What is the strongest magnet?

At present, the magnet with the highest performance is rare earth magnet, and NdFeB is the magnet with the strongest performance among rare earth magnets. But in the environment above 200 degrees Celsius, samarium and cobalt are the strongest magnets.

[Edit this paragraph] Types of magnets

Magnets, which should be called magnetic steel, are mainly divided into two categories, one is soft magnetic and the other is hard magnetic;

Soft magnetic includes silicon steel sheet and soft magnetic core; Hard magnets include Al-Ni-Co, Sm-Co, Ferrite and NdFeB, among which Sm-Co is the most expensive, Ferrite is the cheapest and NdFeB has the highest performance, but Al-Ni-Co has the most stable performance and the best temperature coefficient. Users can choose different hard magnetic products according to different needs.

How to define the performance of a magnet?

There are mainly the following three performance parameters to determine the performance of the magnet:

Remanence Br: The permanent magnet is magnetized to technical saturation, and the retained Br is called remanence induction intensity after the external magnetic field is removed.

Coercive force Hc: To reduce the B of a permanent magnet magnetized to technical saturation to zero, the required reverse magnetic field strength is called magnetic induction coercive force, which is very simple.

Called coercivity

Magnetic energy product BH: indicates the magnetic energy density established by the magnet in the air gap space (the space between the two poles of the magnet), that is, the static magnetic energy per unit volume of the air gap. Because this energy is equal to the product of Bm and Hm of the magnet, it is called magnetic energy product.

Magnetic field: the space that produces magnetic effect on the magnetic pole is the magnetic field.

Surface magnetic field: the magnetic induction intensity at a specific position on the surface of a permanent magnet.

How to choose a magnet?

What role should the magnet play before deciding which kind of magnet to choose?

Main functions: moving objects, fixing objects or lifting objects.

Required magnet shape: disc, ring, square, tile or special shape.

Required magnet dimensions: length, width, height, diameter and tolerance, etc.

Attraction of required magnets, expected price and quantity, etc.

The compass was invented according to the characteristics of magnets.

[Edit this paragraph] The role of magnets

1 refers to the north and south.

Attract light and small objects.

Electromagnets can be used as electromagnetic relays.

4 generator

Discovery of magnetic phenomena

In the pre-Qin era, our ancestors have accumulated a lot of knowledge in this field, and they often encounter magnetite, that is, magnetite (the main component is ferroferric oxide) when exploring iron ore. These findings have long been recorded. These discoveries were first recorded in several articles in Guanzi: "There are magnets on the mountain and gold and copper under it."

There are similar records in other ancient books, such as Shan Hai Jing. The iron-absorbing characteristics of magnets have long been discovered. The main chapter of the nine volumes of Lu's Spring and Autumn Annals is: "Kindly absorb iron, or absorb it." At that time, people called "magnetism" "kindness". They think that magnets attract iron is the attraction of loving mothers to their children. And think: "Stone is the mother of iron, but there are two kinds of stones: kind and unkind. Kindness can attract his children, but not kindness. " Before the Han Dynasty, people wrote magnets as "Guanyin Stone", which means love stone.

Since magnets can attract iron, can they attract other metals? Our ancestors made many attempts and found that magnets can not only attract metals such as gold, silver and copper, but also attract bricks and tiles. During 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. Now people all know that magnets have two poles, one is called N pole and the other is called S pole. Like-sex repulsion, opposites attract. People didn't know this truth at that time, but they could still perceive this phenomenon.

In the Western Han Dynasty, there was an alchemist named Luan Da. He used this characteristic of magnet to make something similar to two chess pieces. By adjusting the mutual position of the polarities of two chess pieces, sometimes the two chess pieces attract each other and sometimes repel each other. Luan Da called it "playing chess". He dedicated the novel to Emperor Wu of the Han Dynasty and gave a live demonstration. Emperor Wu of the Han Dynasty was pleasantly surprised. He was named "General Five Blessingg". Luan made great use of the properties of magnets to make novel things to deceive Emperor Wu of Han Dynasty.

The earth is also a big magnet, and its poles are close to the geographical south pole and the geographical north pole respectively. So the magnets on the earth's surface can rotate freely.

When moving, magnets will repel each other because of the same sex, and the nature of opposites attracting will indicate the north and south. The ancients did not understand this truth, but they knew this phenomenon very well.

Application of magnetic phenomena

"Application in traditional industries":

When talking about magnetic sources, electromagnetic induction and magnetic devices of magnetic materials, we have mentioned some practical applications of magnetic materials. In fact, magnetic materials have been widely used in all aspects of traditional industry.

For example, electrification is impossible without magnetic materials, because power generation requires generators, power transmission requires transformers, motors require motors, and telephones, radios and televisions require speakers. Magnetic steel coil structure is used in many instruments. These have been mentioned in other contents.

"Application of magnetism in biology and medicine";

Pigeon lovers know that if pigeons are released hundreds of kilometers away, they will automatically return to their nests. Why do pigeons have such a good housekeeping skill? It turns out that pigeons are very sensitive to the earth's magnetic field, and they can use the changes of the earth's magnetic field to find their own home. If you tie a magnet to the pigeon's head, it will get lost. If pigeons fly over the radio tower, strong electromagnetic interference will also disorientate them.

In medicine, we can diagnose abnormal tissues of human body and judge diseases by using the familiar nuclear magnetic resonance imaging technology. Its basic principle is as follows: the nucleus is positively charged and spins. Usually, the arrangement of nuclear spin axes is irregular, but when it is placed in an external magnetic field, the spatial orientation of nuclear spin changes from disorder to order. The magnetization vector of the spin system increases gradually from zero, and when the system reaches equilibrium, the magnetization reaches a stable value. If the nuclear spin system is acted by external force at this time, for example, a certain frequency of radio frequency excites the nuclear, it can cause * * * vibration effect. After the RF pulse stops, the nuclei excited by the spin system can't maintain this state, but will return to the original arrangement state in the magnetic field, and at the same time release weak energy into radio signals, which can be detected in time and spatially resolved to obtain the distribution image of the moving nuclei. The characteristic of NMR vibration is that the flowing liquid does not produce signal, which is called flow effect or flow blank effect. So blood vessels are gray-white tubular structures, while blood is black and has no signal. This makes it easy for blood vessels to separate soft tissues. Normal spinal cord is surrounded by cerebrospinal fluid, which is black and has white dura mater set off by fat, which makes the spinal cord show white strong signal structure. Nuclear magnetic resonance (NMR) vibration has been applied to imaging diagnosis of various systems in the whole body. The best effect is the brain, its spinal cord, heart blood vessels, joint bones, soft tissues and pelvic cavity. For cardiovascular diseases, we can not only observe the anatomical changes of heart cavities, great vessels and valves, but also analyze ventricles for qualitative and semi-quantitative diagnosis. We can also make multiple sections with high spatial resolution to show the whole picture of heart and lesions and their relationship with surrounding structures, which is superior to other X-ray imaging, two-dimensional ultrasound, nuclides and CT examinations.

Magnetism can not only diagnose, but also help treat diseases. Magnets were used blindly in ancient medicine in China. Now people use the magnetic differences of different components in blood to separate red blood cells from white blood cells. In addition, the interaction between magnetic field and human meridians can realize magnetotherapy, which has a unique role in treating many diseases and has been applied to magnetic therapy pillows, magnetic therapy belts and so on. The iron remover made of magnet can remove iron powder that may exist in flour, magnetized water can prevent boiler from scaling, and magnetized seeds can improve crop yield to some extent.

"The application of magnetism in astronomy, geology, archaeology and mining";

We already know that the earth is a huge magnet, so where does its magnetism come from? Has it existed since ancient times? What does it have to do with geological conditions? What is the magnetic field in the universe?

At least in the pictures, we have all seen the splendid Northern Lights. China has recorded the Northern Lights since ancient times. The northern lights are actually the result of the interaction between particles in the solar wind and the geomagnetic field. The solar wind is a stream of high-energy charged particles emitted by the sun. When they reach the earth, they interact with the geomagnetic field, just as a wire with current is forced in the magnetic field, which makes these particles move and gather to the north and south poles, and collide with the thin gas in the high altitude of the earth. As a result, gas molecules are excited and emit light.

Sunspots are areas where solar magnetic field activity is very strong. The eruption of sunspots will have an impact on our lives, such as temporarily interrupting radio communication. Therefore, the study of sunspots is of great significance to us.

Geomagnetic changes can be used to explore mineral deposits. Because all substances have strong or weak magnetism, if they gather together to form sediments, it will inevitably interfere with the geomagnetic field in the nearby area and make the geomagnetic field abnormal. According to this, we can measure the earth's magnetism on land, sea or air, obtain geomagnetic maps, analyze and further explore areas with abnormal magnetic fields on the geomagnetic maps, and often find unknown mineral deposits or special geological structures.

Rocks of different geological ages often have different magnetic properties. Therefore, we can judge the geological age change and crustal change according to the magnetism of rocks.

Many mineral resources are * * *, which means that several minerals are mixed together and have different magnetic properties. Using this feature, people developed a magnetic separator. Minerals with different components have different magnetic properties, and the magnetic strength is different. These substances are attracted by magnets, so the attraction is different. Therefore, mixed minerals with different magnetism can be separated to realize magnetic beneficiation.

"The application of magnetism in the military field";

Magnetic materials are also widely used in the military field. For example, ordinary mines or mines can only explode when they hit the target, so their functions are limited. If a magnetic sensor is installed on a mine or a mine, because the tank or warship is made of steel, when they approach (do not touch the target), the sensor can detect the change of the magnetic field, which makes the mine or mine explode and improves the lethality.

In modern warfare, air superiority is one of the keys to winning the battle. However, the aircraft is easily found by enemy radar during flight, which is very dangerous. In order to avoid the surveillance of the enemy radar, a special magnetic material-absorbing material can be coated on the surface of the aircraft, which can absorb the electromagnetic waves emitted by the radar, so that the radar electromagnetic waves are rarely reflected, so that the enemy radar can not detect the radar echo, find the aircraft, and make the aircraft achieve the purpose of stealth. This is the famous "stealth plane". Stealth technology is a hot spot in the field of world military scientific research. The American F 1 17 stealth fighter is an example of the successful application of stealth technology.

In the "Star Wars" plan of the United States, there is a new weapon "electromagnetic weapons". Traditional artillery uses the thrust generated by the instantaneous expansion of ammunition when it explodes to accelerate the projectile quickly and push it out of the bore. The electromagnetic gun puts the shell in the solenoid and energizes the solenoid, then the magnetic field generated by the solenoid will give a great impetus to the shell and shoot it out. This is the so-called electromagnetic gun. Similar to electromagnetic missiles.

[Edit this paragraph] Magnet knowledge

There are many kinds of magnets, which are generally divided into permanent magnets and soft magnets. When we talk about magnets, we usually mean permanent magnets.

Permanent magnets are divided into two categories:

The first category is: metal alloy magnets include Nd2Fe 14B, SmCo and ALNiCO.

The second type is ferrite.

1, neodymium magnet: it is the magnet with the highest commercial performance found at present, and it is called the magnetic king. It has extremely high magnetism and its magnetism reaches the maximum.

The energy product (BHmax) is 10 times higher than that of ferrite. Its machinability is also quite good. Working temperature can be as high as

Up to 200 degrees Celsius. But also because of its hard texture, stable performance, good cost performance and wide application. But because of its chemical activity

It is very strong, so its surface must be treated. (such as zinc plating, nickel plating, electrophoresis, passivation, etc. ).

2. Ferrite magnet: Its main raw materials include BaFe 12O 19 and SrFe 12O 19. Made of ceramic technology, hard texture, belonging to

Brittle materials have become the most widely used permanent magnets because of their good temperature resistance, low price and moderate performance.

3. Al-Ni-Co magnet: It is an alloy composed of trace metal elements such as aluminum, nickel, cobalt and iron. The casting process can be processed into

Different sizes and shapes, good machinability. The reversible temperature coefficient of cast Al-Ni-Co permanent magnet is the lowest, and the working temperature can reach 600℃.

Above degrees. Al-Ni-Co permanent magnet products are widely used in various instruments and other application fields.

4.SmCo can be divided into SmCo5 and Sm2Co 17 according to different components. Its development is limited by the high price of its materials. samarium (Sm)

As a rare earth permanent magnet, cobalt (SmCo) not only has high magnetic energy product (14-28MGOe), reliable coercivity and good temperature characteristics.

Make love. Compared with neodymium magnet, samarium cobalt magnet is more suitable for working in high temperature environment.

[Edit this paragraph] History of magnets

With the development of society, magnets are widely used, ranging from high-tech products to the simplest packaging magnets.

Or neodymium magnets and ferrite magnets. From the development history of magnets, people mainly used carbon at the end of 19 and the beginning of the 20th century.

Steel, tungsten steel, chromium steel and cobalt steel are used as permanent magnet materials. At the end of 1930s, Al-Ni-Co magnet was successfully developed, which led to its large-scale application.

Use becomes possible. In 1950s, the appearance of barium ferrite magnets not only reduced the cost of permanent magnets, but also broadened the application scope of permanent magnet materials to

High frequency field. In 1960s, the appearance of samarium-cobalt permanent magnets opened up a new era for the application of magnets. Dayton, USA 1967

University Strnat, etc. The development of samarium cobalt magnet marks the arrival of the era of rare earth magnets. So far, the rare ten permanent magnets have experienced the first generation.

SmCo5, the second generation precipitation hardening Sm2Co 17, has developed into the third generation NdFeB permanent magnet. At present, ferrite magnets are the most widely used.

Permanent magnet materials, but the output value of neodymium magnet has greatly exceeded that of ferrite permanent magnet materials, and the production of neodymium magnet has developed into a big industry.

The magnetic force is arranged as follows: neodymium magnet, samarium cobalt magnet, Al-Ni-Co magnet and ferrite magnet.

Manufacturing technology of magnets: Nd magnets, Sm-Co magnets, Al-Ni-Co magnets and ferrite magnets have different manufacturing technologies.

1, Neodymium magnet Technically, there are sintered Nd magnets and bonded Nd magnets. We mainly talk about sintered Nd magnets.

[Edit this paragraph] Neodymium magnet technology

Process flow: batching → smelting and ingot making → milling → pressing → sintering and tempering → magnetic detection → grinding → pin cutting and adding.

Work → electroplating → finished product. Among them, batching is the foundation and sintering tempering is the key.

Neodymium magnet production tools: melting furnace, crusher, ball mill, jet mill, pressure forming machine, vacuum packaging machine, isostatic press,

Sintering furnace, heat treatment vacuum furnace, magnetic performance tester, Gauss meter.

Neodymium magnet processing tools: special slicer, wire cutter, flat grinder, double-sided machine, punch, chamfering machine, plating equipment.

[Edit this paragraph] What is a maglev train?

Maglev train is a high-speed maglev train system with contactless electromagnetic levitation, guidance and drive system. Its speed can reach more than 500 kilometers per hour, making it the fastest ground passenger transport in the world today. It has the advantages of high speed, strong climbing ability, low energy consumption, low noise during operation, safety and comfort, no oil consumption and little pollution. And the overhead way is adopted, which occupies less cultivated land. Maglev train refers to the use of the basic principle of magnetic force to suspend these trains on the guide rail to replace the old steel wheels and track trains. Magnetic levitation technology uses electromagnetic force to lift the whole train car, get rid of annoying friction and unpleasant clang, and realize rapid "flight" without touching the ground and fuel.