Why can high temperature resistant magnets maintain magnetic stability at high temperatures?

In many fields such as aerospace, automobile manufacturing, and power electronics, high temperature environments pose severe challenges to the performance of magnets. Traditional magnets are prone to magnetic attenuation or even demagnetization at high temperatures, and the emergence of high temperature resistant magnets provides key support for the development of these fields.

High temperature resistant magnets mainly include NdFeB magnets, SmCo magnets, AlNiCo magnets, and ferrite magnets. Different types of high temperature resistant magnets have their own unique characteristics.

NdFeB magnets are one of the more common and high performance high temperature resistant magnets on the market. It has extremely high magnetic properties, and its BHmax is more than 10 times higher than that of ferrite. In terms of operating temperature, high performance NdFeB magnets can operate at temperatures up to 200 degrees Celsius, and some specially designed NdFeB magnets can even maintain magnetism in high temperature environments above 400 degrees Celsius. However, NdFeB magnets are chemically active, and to prevent corrosion, they usually require surface treatments such as electroplating zinc, nickel, gold, and epoxy.

Samarium cobalt magnets can be divided into SmCo5 and Sm2Co17 according to their composition. As a rare earth permanent magnet, it not only has a high magnetic energy product (14-28MGOe), but also has reliable coercive force and good temperature characteristics. Samarium cobalt magnets can maintain their magnetic force unchanged in high temperature environments, can withstand high temperature working environments far above 500℃-600℃, and have a high Curie temperature, which enables them to stably play a magnetic role in high temperature environments.

Alnico magnets are alloys composed of aluminum, nickel, cobalt, iron and other trace metals, and can be made into various sizes and shapes through a casting process. It has good machinability, and cast Alnico permanent magnets have the lowest reversible temperature coefficient and can operate at temperatures up to 600 degrees Celsius.

The main raw materials of ferrite magnets are BaFe12O19 and SrFe12O19, which are made using ceramic technology. It is a hard and brittle material with temperature resistance, low cost and moderate performance, and is one of the most widely used permanent magnets.

High temperature resistance principle of high temperature resistant magnets
The reason why high temperature resistant magnets can maintain stable magnetic properties in high temperature environments is due to their special physical and chemical structure. From a microscopic point of view, the magnetism of magnets comes from the magnetic moments generated by the spin and orbital motion of electrons inside atoms. At normal temperature, the arrangement of these magnetic moments has a certain order, thus forming macroscopic magnetism.

When the temperature rises, the thermal motion of atoms intensifies, which will interfere with the arrangement of magnetic moments. For ordinary magnets, as the temperature rises, the orderly arrangement of magnetic moments is gradually destroyed, resulting in weakened magnetism. High temperature resistant magnets enhance the interaction between magnetic moments through special material formulations and microstructure design, so that they can still maintain a relatively stable arrangement at high temperatures.

For example, the specific atomic arrangement of rare earth elements samarium and cobalt in samarium cobalt magnets forms a stable magnetic structure that can resist the interference of thermal motion caused by high temperature, thereby maintaining high magnetic properties. At the same time, the crystal structure of high temperature resistant magnets also has high thermal stability, can withstand high temperatures without obvious phase changes, and further ensures the stability of its magnetism.

Production process of high temperature resistant magnets
The production process of high temperature resistant magnets has an important influence on their performance. Taking NdFeB magnets as an example, common production processes include sintered NdFeB and bonded NdFeB.

Sintered NdFeB is made by powder metallurgy. First, the raw materials of NdFeB are smelted and powdered, then pressed and formed, sintered at high temperature to densify the magnet, and finally the finished product is obtained by mechanical processing and surface treatment. Sintered NdFeB has extremely high magnetic energy product and coercive force, but its texture is hard and brittle, and it is prone to defects such as cracks during processing.

Bonded NdFeB is a composite magnet made by uniformly mixing NdFeB powder with resin, plastic or low melting point metal, and then pressing, extruding or injection molding. Bonded NdFeB has magnetism in all directions and can be processed into thin-walled rings or thin magnets with complex shapes. It has high dimensional accuracy and can arbitrarily select the magnetization direction of the magnet. However, the magnetic properties of bonded NdFeB are lower than those of sintered NdFeB.

The production process of samarium cobalt magnets is relatively complex, requiring precise control of the composition and proportion of raw materials, as well as parameters such as sintering temperature and time. During the production process, it is necessary to ensure that the microstructure of the magnet is uniform and dense to achieve good magnetic properties and high temperature resistance.

Application fields of high temperature resistant magnets
High temperature resistant magnets are widely used in many fields. In the aerospace field, high temperature magnets can be used to manufacture magnetic sensors, power equipment, and key components in high-speed rotators and control systems of aircraft. Since aerospace equipment will face extreme environments such as high temperature, high pressure, and strong radiation during operation, the stable performance of high temperature resistant magnets can ensure the reliability and safety of the equipment.

The automotive manufacturing field is also an important application market for high temperature resistant magnets. In the manufacture of components such as automobile engines, generators, starters, and electric power steering systems, high temperature resistant magnets play a key role. For example, in automobile engines, high temperature resistant magnets can be used to manufacture the core of ignition coils to improve ignition efficiency and thus improve engine performance.

In the field of power electronics, high temperature resistant magnets are widely used in motors, generators, transformers, electromagnetic pumps and other equipment due to their high magnetic permeability and low energy consumption. In the petrochemical industry, high-temperature magnets can be used in various reactors, separators, compressors and other equipment to achieve automatic control of equipment and optimize the production process.

In the field of medical devices, high-temperature magnets are often used to manufacture precision parts of equipment such as magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR) to improve the accuracy and stability of the equipment. In addition, high-temperature magnets are also used in astronomy, geological exploration, thermal processing, magnetic descaling, magnetic therapy and other fields.

Development trend of high-temperature resistant magnets
With the continuous advancement of science and technology, the development of high-temperature resistant magnets has shown some obvious trends. In terms of performance improvement, high-temperature resistant magnets are expected to have higher magnetic energy product, better temperature stability and stronger corrosion resistance in the future. By improving material formulations and production processes, R&D personnel can further improve the magnetic properties of magnets so that they can maintain stable magnetism at higher temperatures.

In terms of application field expansion, high-temperature resistant magnets may be used in more high-temperature, high-strength, and highly corrosive environments, such as nuclear energy, deep-sea exploration and other fields. In the field of nuclear energy, high-temperature resistant magnets can be used in key components such as the control rod drive mechanism of nuclear reactors to ensure the safe and stable operation of nuclear reactors. In the field of deep-sea exploration, high-temperature resistant magnets can be used to manufacture sensors and drive devices for deep-sea detectors to adapt to the harsh environment of high pressure and high temperature in the deep sea.

In terms of environmental protection and sustainable development, the future production of high-temperature resistant magnets will pay more attention to environmental protection and the rational use of resources. R&D personnel will be committed to developing new environmentally friendly materials and production processes to reduce the impact on the environment, while improving the utilization rate of resources and achieving sustainable development of the high-temperature resistant magnet industry.

As a magnetic material with stable performance in high-temperature environments, high-temperature resistant magnets play an irreplaceable role in modern industry and science and technology. With the continuous advancement of technology, the performance of high-temperature resistant magnets will continue to improve, and the application field will continue to expand, making greater contributions to the development of human society.