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What is NdFeB hydrogenation crushing HD method

What is NdFeB hydrogenation crushing HD method

Aug 29,2022

The NdFeB hydrogenation pulverization HD method is only suitable for the coarse crushing and middle grinding of hydrogenated metals or alloys. The feed size is 100-0.1MM, and the powder size is 10-1000UM. Need powder, this particle size has met practical requirements. The powder particle size of NdFeB permanent magnets should be 3-5UM, and it needs to be finely ground by jet mill. The NdFeB hydrolysis (HD) method is to refine the particle size by hydrogen absorption lattice expansion and dehydrogenation reduction, and hydrogen absorption or dehydrogenation is a reversible chemical reaction process, and the physical and chemical reactions have changes in its chemical composition and magnetic properties. NdFeB absorbs hydrogen, the resulting hydride lattice expands, and generates heat, a chemical process; the internal stress of the expansion makes the NdFeB crystal crack into a loose body, which is a physical phenomenon, both of which are carried out at the same time; heating dehydrogenation treatment, most of the main The phase hydride changes back to the original Nd2Fe14B powder, and some residual Nd-rich phase hydride needs advanced treatment. In the hydrogen absorption process of NdFeB, the first hydrogen absorption is the Nd-rich phase exposed on the surface, followed by the reaction of the main phase Nd2Fe14B with H2, the formation of the main phase hydride is accompanied by an exothermic reaction, and the total heat can make the reactant temperature Raised to 300 degrees. The lattice constant becomes larger and the thermal expansion process produces powder explosion, and the HD powder of NdFeB has undergone qualitative change. Dehydrogenation turns Nd2Fe14Bhy into Nd2Fe14B, i.e. decomposition of the hydride. Effects of temperature and pressure, 650℃, the Nd-rich phase changes and melts, and the HDDE reaction occurs when the temperature continues to rise. The optimal dehydrogenation temperature is 500 ℃, Under this condition, all the hydrogen of the main phase hydride is released, and the NdH3 of the neodymium-rich phase hydride is 500. After C, part of the hydrogen is removed to become NdH2, 1040.℃ can completely discharge hydrogen from the main phase Nd2Fe14B.

Advantages and disadvantages of HD hydrogenation pulverization method of NdFeB alloy magnetic powder

①The milling efficiency of HD+JM (jet mill) is increased by 2-3 times, reaching 90-100KG/HR (original only 30KG/HR); it is close to the main phase composition of NDFEB (RE=11.76at%) in terms of mechanical properties, and Hard and tough (Hv=530, flexural strength 24-26KG/mm2);


Effectively reduce the oxygen content of NdFeB alloy magnetic powder. The HD hydrogenation pulverization method effectively reduces the oxidation degree of the grinding section ((200-800)×10-O2), and the presence of hydrogen in the sintering process can reduce the amount of neodymium Oxide, purifies grain boundaries and promotes densification, realizing partial activation sintering.


HD powder is mostly cracked along the grain boundary phase: HD+JM powder is mostly single crystal particles, close to the optimal particle size of 2-3UM, and the edges of the grains have neodymium-rich phases, which can effectively improve IHC, which can actually increase by 500-5000Oe.


The properties of HD NdFeB alloy magnetic powder vary slightly: HD+JM powder exists in the form of oxide due to part of the powder, its magnetic variation presents: 4πJs high, Br and IHC low phenomenon, weak magnetic, easy demolding, neat appearance, stacking convenient;


HD powder has good oxidation resistance: HD+JM powder has good oxidation resistance, and the storage time is long. Practice shows that the powder of ≥ 4UM is not easy to burn in the air.