The second process in the magnet production process: hydrogen crushing

The rare earth raw material of the magnet is cooled by smelting and smelting in the melting furnace to make a strip, and then enters the hydrogen crushing section, which is the coarse crushing and medium grinding of rare earth alloy. The feed size is 100-- 0.1mm, and the output particle size is 10-1000um.The powder size of ndFeb permanent magnet should be 3-5um, which should be ground by air flow.Hydrogenation crushing (HD) method is hydrogen absorption lattice expansion and dehydrogenation reduction to refine particle size, and hydrogen absorption or dehydrogenation is a reversible chemical reaction process, physical chemical reaction exists in its chemical composition and magnetic changes.

Ndfeb crystal absorbs hydrogen, and the hydride lattice expands and generates heat, a chemical process;The internal stress of expansion causes ndFeb crystal to crack into loose body. It is a physical phenomenon. Both of them occur simultaneously.Heating dehydrogenation treatment, most of the main phase hydrides changed back to the original Nd2Fe14B powder, some residual ND-rich phase hydrides need deep treatment.During the hydrogen absorption process of NdFeb, the ndF-rich phase is exposed to the surface at first, followed by the main phase Nd2Fe14B which reacts with H2. The formation of main phase hydride is accompanied by exothermic reaction. The total heat can raise the temperature of the reactant to 300 degrees.In the process of lattice constant increasing and thermal expansion, powdery burst occurs. The HD powder of NdFeb has undergone qualitative change.

Dehydrogenation turns Nd2Fe14Bhy into Nd2Fe14B, which is the hydride decomposition.Now the optimal dehydrogenation temperature is 500℃. Under this condition, all the hydrogen of the primary phase hydride is released. After 500℃, the neodymium-rich phase hydride NdH3 dehydrogenates part of the hydrogen into NdH2 and 1040℃ can completely discharge hydrogen from the primary phase Nd2Fe14B

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