As a rare earth permanent magnet material with the strongest magnetic properties in commercial use, NdFeB permanent magnet (NdFeB) is widely used in many fields such as motors, speakers, wind power generation equipment and precision instruments. However, compared with other types of permanent magnet materials, the stability of NdFeB permanent magnet in high temperature environment has always been widely concerned.
First of all, it is necessary to clarify a basic concept-the Curie temperature of the magnet. The Curie temperature refers to the critical temperature at which the magnet material loses its magnetism. For NdFeB, this temperature is usually between 310℃ and 380℃ (depending on the added elements and material formula). When the temperature approaches or exceeds the Curie point, the magnetic moment arrangement inside the NdFeB will be severely damaged, the magnetism will drop sharply, or even disappear completely. Therefore, NdFeB permanent magnet does have the risk of demagnetization at high temperature.
Secondly, even if the Curie temperature is not reached, the coercive force and magnetic energy product of NdFeB permanent magnet will decrease with the increase of temperature. Above 80℃, the magnetic properties of ordinary NdFeB permanent magnet will begin to decline significantly. For example, when the temperature of a common N35 grade ndfeb permanent magnet rises to 100℃, the remanence may drop by 3%~5%, and at 150℃, its magnetic properties may drop by more than 15%. Long-term operation under high temperature conditions may also lead to irreversible "thermal demagnetization", and the magnetic properties cannot be fully restored even after cooling.
In order to deal with the demagnetization problem in high temperature environment, R&D personnel usually take several technical paths for optimization. One is to improve the thermal stability of the material, for example, by adding heavy rare earth elements such as dysprosium (Dy) or gadolinium (Gd) to the raw materials to enhance the high temperature resistance of the magnet; the second is to select high temperature resistant grade magnets, such as N45SH, N42UH, N35EH, etc. These models can withstand working environments of 150℃, 180℃ or even above 200℃ respectively; the third is to reduce the oxidation and corrosion effects of the environment on the surface of the magnet through coating and packaging technology, thereby indirectly slowing down the performance degradation.
Of course, although the high temperature resistant ndfeb permanent magnet has more stable performance, it also faces challenges such as high cost and difficult processing. Heavy rare earth elements are expensive and scarce, and their fragile and crackable properties during processing also make the manufacturing process more complicated. Therefore, in practical applications, designers often need to balance magnetic properties, temperature requirements, volume restrictions and costs, and choose the most suitable magnet brand and cooling protection measures.
In practical industrial applications, such as new energy vehicle drive motors, servo control systems or wind power generation yaw systems, ndfeb permanent magnets must operate for a long time between 80℃ and 180℃. In order to ensure its long-term reliability, it is usually used with an efficient heat dissipation system, a forced cooling mechanism or a temperature sensing protection device to prevent the motor from overheating and causing the magnet performance to deteriorate. In the field of medical equipment or aerospace, the high-temperature stability requirements of magnets are more stringent, and the use of high-grade brands has become standard.
Ndfeb permanent magnets do have the risk of demagnetization in high temperature environments, but by selecting appropriate material formulations, process technologies and system structure designs, the demagnetization problem can be effectively alleviated or even avoided. When selecting the model, factors such as operating temperature, load cycle and environmental changes should be fully considered, and the magnet brand and protection scheme should be reasonably matched to ensure stable operation of the equipment. In the future, with the development of new material technology, the application potential of NdFeB in high-temperature fields will be further expanded.
