Three environmental factors affecting the function of high-temperature magnet
Because the sintered NdFeB has a negative temperature coefficient （αBr<-0.13%/℃，αHcj<-0.6%/℃）, the highest instantaneous temperature and the continuation of the highest temperature will demagnetize the magnet to varying degrees, including reversible and non-reversible, recoverable and non-recoverable.
Neodymium is easy to corrode and oxidize. Generally, we adopt surface treatment to maintain permanent magnets, but it can not fundamentally deal with the impact of environmental humidity on the magnets. The more boring the environment is, the longer the service life of the magnet will be. How to measure the concavo-convex of magnetic function?
There are three main parameters: Residual Induction (Br), is a measure of the magnetic field strength that a magnet can supply to the outside world; Coercive Force (Hc), is a measure of anti-demagnetization ability; BHmax, is to measure how much energy can be stored.
Permanent magnets are divided into two categories:
1 Metal alloy high-temperature magnets include NdFeB high-temperature magnets Nd2Fe14B, SmCo high-temperature magnets, AlNiCo high-temperature magnets.
2 Ferrite permanent magnets high-temperature magnets: its atom internal structure of the contrast No, it has magnetic moment itself.
High-temperature resistant magnets are divided into permanent high-temperature resistant magnets and soft magnets. Permanent high-temperature resistant magnets are added with strong magnets so that the spin and electron angular momentum of magnetic materials are arranged in a fixed direction. Soft magnets are added with current (also a method of adding magnetic force).
Different properties of high-temperature magnets have different composition characteristics, and the magnitude of the magnetic force is also different.
Generally, high-temperature resistant magnets can be divided into four categories according to their different types:
1. Neodymium high-temperature magnet: It is now found in the commercial function of the highest high-temperature magnet, known as the magnet king, has a very high magnetic function. Its BHmax is higher more than 10 times of ferrite. Its own machining function is also quite good. The operating temperature can reach up to 200 degrees Celsius. And its hard texture, stable function, has a good cost performance, but because of its strong chemical activity, it is necessary to its surface layer treatment.
2, Ferrite high-temperature resistant magnet: its main raw materials include BaFe12O19 and SrFe12O19. Made by ceramic technology, the material is hard and brittle, because ferrite high-temperature magnet has excellent heat resistance, low price, moderate function, has become the most widely used permanent magnet.
3. AlNiCo high-temperature resistant magnet: It is an alloy composed of aluminum, nickel, cobalt, iron and other trace metal elements. Forging technology can produce different yardsticks and shapes, with excellent workability. Forged aluminum nickel cobalt permanent magnet has the lowest reversible temperature coefficient, and the working temperature can be as high as 600 degrees Celsius. AlNiCo permanent magnets are widely used in various instruments and other applications.
4. Samarium cobalt (SmCo) is divided into SmCo5 and Sm2Co17 according to the different components. Because its information is expensive, its development is restricted. SmCo, as a rare earth permanent high-temperature magnet, not only has a high magnetic energy product (14-28MGOe), strong coercivity and outstanding temperature characteristics. Compared with Nd-Fe-B magnets, samarium cobalt high-temperature magnet is more suitable for working in the high-temperature environment. The midpoint of a bar-shaped high-temperature magnet is suspended by a thin line. When it stops, its ends will point to the south and north of the earth.