The second process of magnet production process: hydrogen crushing

Rare earth raw material of magnet is melted and cooled in smelting furnace to make flip strip. It enters hydrogen crushing section, which is crushing and grinding of rare earth alloy. The feed size is 100-0.1MM, and the powder size is 10-1000UM. The powder size of Nd-Fe-B permanent magnet should be 3-5UM, which needs air grinding and fine grinding. Hydrogenation fragmentation (HD) method is a process of hydrogen absorption lattice expansion and dehydrogenation reduction to refine particle size. Hydrogen absorption or dehydrogenation is a reversible chemical reaction process. There are changes in chemical composition and magnetic properties in physical and chemical reactions.

Nd-Fe-B crystal absorbs hydrogen, and the hydride lattice expands, and generates heat and chemical process; the internal stress of expansion causes cracks in Nd-Fe-B crystal to become loose body, which are both physical phenomena. After heating and dehydrogenation treatment, most of the main phase hydrides turn back to the original Nd2Fe14B powder, and some of the residual Nd-rich phase hydrides need further treatment. In the process of NdFeB hydrogen absorption, the Nd-rich phase exposed on the surface is the first to absorb hydrogen, followed by the reaction of the main phase Nd2Fe14B with H2. The formation of the main phase hydride is accompanied by exothermic reaction, and the total heat can raise the temperature of the reactant to 300 degrees. With the increase of lattice constant and thermal expansion, powder explosion occurs, and NdFeB HD powders have undergone metamorphism.

Dehydrogenation transforms Nd2Fe14Bhy into Nd2Fe14B, which is the decomposition of hydride. The effect of temperature and pressure, 650. At C, Nd-rich phase transition melts softly and HDDE reacts with continuous heating. Now the optimum dehydrogenation temperature is 500. C. Under these conditions, all the hydrogen of the main phase hydride is released, and NdH3, a neodymium-rich phase hydride, is 500. After C, some of the hydrogen was removed and converted to NdH2, 1040. C can completely discharge hydrogen from the main phase Nd2Fe14B.

Hydrogen crushing in the second process of magnet production


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