High Abundance Cerium Magnets
With the continuous expansion of the application field of sintered NdFeB and the rapid growth of output, the corresponding rare earth resources have also been exploited in large quantities. Various rare earth elements in rare earth ores are symbiotic, but in the preparation process of NdFeB, mainly praseodymium Pr and neodymium Nd elements with a mass fraction of 25% in light rare earths are used, so the proportion of light rare earths is The utilization rate of cheap rare earths such as 49% cerium Ce and 23% lanthanum La is very low.
In recent years, the market price of rare earth materials such as praseodymium and neodymium has fluctuated greatly, which has caused great troubles and constraints to production enterprises in terms of raw material costs. Since the birth of sintered NdFeB, the work of finding the replacement elements of Nd has begun. Ce is the most abundant metal element among all rare earth elements, and its price is less than one tenth of that of Pr and Nd. The anisotropy field and phase stability are also higher than those of La2Fe14B, and the advantages of high reserves and low cost of Ce naturally make Ce replace Pr-Nd a research hotspot in the industry.
The team of academician Li Wei of the China Iron and Steel Research Institute has spared no effort in the research, development and promotion of cerium magnet industrialization. At present, almost all NdFeB manufacturers in China have been involved in the development and production of cerium magnets. The annual output of new cerium magnets has reached about 50,000 tons, and the scale has a tendency to expand.
The figure above shows the intrinsic properties of RE2Fe14B compounds of different rare earth elements at (22°C). It can be seen that the saturation magnetic polarization, magnetocrystalline anisotropy field and Curie temperature of Ce2Fe14B are lower than those of Pr2Fe14B and Nd2Fe14B, Ce The introduction will inevitably lead to the decline of magnet performance and the deterioration of temperature resistance. Since the activity of cerium element is higher than that of praseodymium and neodymium, the anti-oxidation requirements are higher in the preparation process; and the paramagnetic CeFe2 phase is easily formed in the grain boundary phase of the cerium-containing magnet. The appearance of the CeFe2 phase reduces the volume fraction of the main phase on the one hand, and on the other hand. On the one hand, this phase has a high melting point and poor fluidity and wettability, which is not conducive to the uniform distribution of the rare earth-rich phase. All of these increase the difficulty of preparing high-performance cerium magnets.
In the initial stage of the industrialization of cerium magnets, more N35-N42 or even low-end grades of N25-N30 magnets with a coercive force of less than 10kOe were produced. In addition, cerium magnets are mostly combined with waste magnet steel technology, and cerium magnets once became the representative of low-grade magnet steel. With the iterative upgrade of production equipment, the popularization and application of advanced technologies such as low-oxygen technology, grain refinement, and double alloy technology, as well as the understanding of the mechanism of performance impact in cerium magnets by production and R&D personnel, a more scientific cerium magnet has been developed. Magnet formula system and preparation process, various types of high energy product cerium magnets have been introduced to the market one after another, combined with grain boundary diffusion technology, it has been able to produce SH, SHT, UH and even EH high temperature resistant products.
The application of sintered NdFeB permanent magnets can be divided into the following directions according to the mechanism:
Utilize the attraction force of magnetic steel on iron, cobalt, nickel and other materials, mainly including magnetic chucks, magnetic separators, sewage processors, smart wearables, luggage buckles, door buckles, educational toys, etc.;
Using Faraday’s law of electromagnetic induction and the principle of Lorentz force. The magnetic steel is used as the magnetic source of permanent magnet motors and permanent magnet generators, including new energy synchronous motors, electric bicycle hub motors, traction machines, servo motors, air-conditioning compressors, direct-drive and semi-direct-drive wind turbines, etc.;
Adjust the coil magnetic field through the change of coil current, and interact with the magnetic field generated by the magnet to generate vibration, including audio speakers, speakers, receivers and VCM motors;
Using magnetic physics principles such as nuclear magnetic resonance and Hall effect, including nuclear magnetic resonance instruments, various sensors, etc.
As shown in the figure above, the application scenarios of cerium magnets have been diversified. In the initial stage of large-scale production, most of the magnets are low-end grades such as N25-N42, which fills the performance gap between high-performance magnets and ferrites in the demand for permanent magnet materials. The application is concentrated in the fields of magnetic adsorption toy magnets, door buckles, luggage buckles, magnetic separators, etc.
As the grades of cerium-containing magnets cover high-performance products such as N45H, N48M, and N52, the application of products has expanded to the fields of electroacoustics, mobile smart terminals, wind power and nuclear magnetic resonance, especially the 38M-38H grades are widely used in the field of electric bicycle hub motors.
High coercive force products produced by combining grain boundary diffusion technology can be used in mining machinery, industrial motors, traction machines, air-conditioning compressors and other fields.