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Hydrogenation and Disproportionation of NdFeB to Improve Magnetic Properties

In-situ XRD study at High-Pressure and High-Temperature with HPC 900

Nd-Fe-B compounds are the most widely used rareearth alloys for the production of strong permanent magnets. The magnets are produced from fine pow-der by sintering or bonding. Coercivity of the powder is decisive for the strength of the final magnet. One of the processes which can be used to optimize the magnetic properties of the powder is the hydrogenation-disproportionation-desorption-recombination process (HDDR). Nd-Fe-B is heated in hydrogen, which causes the material to decompose into a-Fe and
Nd-hydride:

Nd2Fe14B + 2H2 -> 2NdH2 + 12α-Fe + Fe2B

Desorption of hydrogen and subsequent recombi- nation of the starting compound by heating under vacuum leads to a very fine grained material with sub-micron grain size.

This report describes an in-situ XRD study of the hydrogenation and disproportionation processes which occur when Nd2Fe14B is heated in hydrogen. Hydrogen pressure and temperature strongly influence grain size and magnetic properties of the final material. The results are compared with data obtained with high-pressure differential thermo- analysis (HDTA).

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