Magnet. It is a material that has the ability to produce a magnetic field on the outside, which is capable of attracting iron , as well as nickel and cobalt .
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- 1 Characteristics of the magnet.
- 2 Magnetism
- 3 Loss of magnetic properties
- 4 Types of permanent magnets.
- 1 Ceramic magnets.
- 2 Alnico magnets.
- 3 Rare Earth Magnets.
- 4 Flexible magnets.
- 5 Other magnets.
In a magnet the attraction capacity is greater at its ends or poles. These poles are called north and south, because they tend to be oriented according to the geographic poles of the Earth , which is a gigantic natural magnet.
The region of space where the action of a magnet is revealed is called the magnetic field. This field is represented by lines of force are imaginary lines, closed, ranging from the north pole to the south pole by outside magnet and counterclockwise inside it; it is represented by the letter B.
It has long been known that an electric current generates a magnetic field around it. Inside the matter there are small closed currents due to the movement of the electrons that contain the atoms , each of them originates a microscopic magnet or dipole . When these small magnets are oriented in all directions, their effects cancel each other out and the material does not have magnetic properties; on the other hand, if all the magnets align they act as a single magnet and in that case we say that the substance has been magnetized.
Loss of magnetic properties
For a magnet to lose its properties it must reach the so-called “Curie temperature” which is different for each composition. For example for a ceramic magnet it is 450 ºC, for a cobalt 800 ºC, etc. Contact demagnetization also occurs, every time we stick something to a magnet we lose part of its properties. Strong shocks can dislodge the particles causing the magnet to lose its power.
Types of permanent magnets.
In addition to natural magnetite or magnet, there are different types of magnets made from different alloys:
- Ceramic or ferrite magnets.
- Alnico magnets.
- Rare earth magnets.
- Flexible magnets.
They are so called because of their physical properties. Its appearance is smooth and dark gray in color, similar to porcelain . They can be given any shape, which is why it is one of the most used magnets ( speakers , headphone rings , cylinders to stick on figures that stick to refrigerators , etc.). They are very fragile, they can break if they fall or approach another magnet without due care.
They are made from very fine particles of ferromagnetic material (iron oxides) that are transformed into a conglomerate by means of heat treatments at high pressure, without exceeding the melting temperature . Another type of ceramic magnets, known as ferrites , are made from a mixture of barium and strontium. They are resistant to many chemical substances (solvents and acids) and can be used at temperatures between _40 ºC and 260 ºC.
They are called like this because in their composition they have the elements aluminum, nickel and cobalt. They are made by melting 8% aluminum, 14% nickel, 24% cobalt, 51% iron and 3% copper . They are the ones with the best behavior at high temperatures. They have the advantage of having a good price, although they do not have much strength.
Rare earth magnets.
They are small, metallic-looking magnets with a strength 6 to 10 times greater than traditional magnetic materials. Boron / neodymium magnets are made of iron, neodymium and boron ; they have high resistance to demagnetization. They are strong enough to magnetize and demagnetize some flexible alnico magnets. Oxidise easily, so they are coated with a bath of zinc , nickel or varnish epoxy and are quite fragile.
Samarium / cobalt magnets do not present oxidation problems but have the drawback of being very expensive. They are being replaced by those of boro_neodymium. It is important to handle these magnets carefully to avoid bodily harm and damage to the magnets (fingers can be seriously pinched).
They are made by agglomerating magnetic particles (iron and strontium) in an elastomer (rubber, PVC, etc.). Its main characteristic is flexibility, they come in the form of rolls or plates with the possibility of an adhesive face. They are used in advertising, fridge locks , coded keys.
They consist of a series of narrow bands that alternate the north and south poles. Right on the surface its magnetic field is intense but it cancels out at a very small distance, depending on the width of the bands. They are done in this way to eliminate problems, such as the magnetic strip of a credit card being erased (they are canceled with the thickness of the leather of a wallet ).
Platinum / Cobalt magnets are very good and are used in watchmaking , aerospace devices, and dentistry to improve retention of full dentures . They are very expensive. Other alloys used are copper / nickel / cobalt and iron / cobalt / vanadium.