Recycled Magnets Research Articles

Coercivity enhancement of recycled Nd–Fe–B sintered magnets by grain boundary diffusion with DyH3 nano-particles

The waste VCM magnets were disassembled from hard disk. After removing the coating of nickel by electrochemical method, the waste VCM magnets were recycled by grain boundary diffusion with DyH3 nano-particles. Compared to that of the original magnet, the coercivity of recycled magnets increases by 11.81kOe, while the remanence keeps almost invariant. Investigation shows that Dy is preferentially enriched as (Nd,Dy)2Fe14B phase in the surface region of the Nd2Fe14B matrix grains indicated by the remarkable enhancement of the magneto-crystalline anisotropy field of the magnet. As a result, the magnet diffused with a small amount of DyH3 nano-particles possesses enhanced coercivity without remarkably sacrificing its magnetization.

Waste Nd-Fe-B Sintered Magnet Recycling by Doping With Rare Earth Rich Alloys

Waste sintered Nd-Fe-B permanent magnets were recycled via doping (Nd <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> Dy <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">80</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">76</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> special alloy (SA) powders. The effect of the SA on the microstructure and magnetic properties of the recycled magnets has been studied. The SA additives between 0.0 and 2.0 wt% have little effect on the remanence (B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ) of the recycled magnet. When the additive content is more than 2.0 wt%, the remanence (B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ) begins to decrease. The coercivity of recycled magnet increases gradually as the SA additive increases. Compared with the properties of the original waste sintered magnet, a magnet recycled with 2.0 wt% SA recovers 97.5%, 92.4%, and 93.1% of B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> , H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cj</sub> and (B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</sub> ) <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> , respectively. The volume fraction of the Nd-rich phase reaches a maximum of 7.4 vol% for 2.0 wt% SA, which is nearly equal to that of the original waste magnet. The average grain size of all the recycled magnets is larger than that of the original waste magnet. It is our conclusion that currently 2.0 wt% SA additive is the best content for recovering the properties of the waste magnets.

Multiple recycling of NdFeB-type sintered magnets

Abstract Some fully dense, sintered NdFeB-type magnets (employed in VCM disc drives) have been subjected to a recycling process using the hydrogen decrepitation (HD) process. After a brief milling treatment, the powder was aligned, pressed and re-sintered and this procedure was repeated four times with a progressive fall in the density and in the magnetic properties. The chemical analysis indicated that this was due to the progressive oxidation of the Nd-rich material and to some Nd loss by evaporation. The procedure was then repeated but with the addition (blending) of a fine powder of neodymium hydride after the first cycle. It was found that the addition of 1 at.% of neodymium at each stage was sufficient to maintain the density and the magnetic properties of the recycled magnets up to and including the 4th cycle. Inductively coupled plasma (ICP) and metallographic analysis indicated that the neodymium hydride additions compensated for the neodymium loss due to evaporation and to oxidation so that the proportion of Nd-rich material remained approximately constant. The additional amount of Nd2O3 in the blended recycled magnets appeared to inhibit grain growth on the 3rd and 4th cycles when compared to that of the unblended magnets. The next challenge is to see if the process can be scaled-up to an industrial scale.

Recycling of rare earth sintered magnets as isotropic bonded magnets by melt-spinning

The waste Ni-coated Nd–Fe–B sintered magnets were recycled as the raw materials for isotropic bonded magnets by using the melt-spinning method. The oxygen content in recycled magnet powders was smaller (<0.1 wt.%) than that in the waste sintered magnet because the oxide slug was separated upper from the molten alloy during the sample preparation for RF melting. The powder with the best magnetic properties ( B r≅0.78 T, H cj ≅ 0.72 MA/m, and (BH) max ≅ 87.8 kJ/m 3) was obtained when the roll surface velocity was 16 m/s. The magnetic properties of the resulting bonded magnet prepared from the above powder were B r≅0.69 T, H cj≅0.70 MA/m, and ( BH) max≅71.0 kJ/m 3. These values are nearly same to the bonded magnet prepared by us from the commercial MQPB powder (MQI Co. Ltd.) with the magnetic properties of B r≅0.73 T, H cj≅0.79 MA/m, and ( BH) max≅86.0 kJ/m 3.

Zero-emission Process for Nd-Fe-B Melt-Spun Powder Used in Epoxy Resin Bonded Magnets.

Epoxy resin is generally used as a binder for consolidating Nd-Fe-B melt-spun powder into a specific shape, because the usage of this binder enables us to obtain a density higher than that of other polymers. Reports concerning methods of recycling melt-spun powder included in epoxy resin bonded magnets, however are sparse. We newly therefore developed a technique for recycling Nd-Fe-B melt-spun powder, using liquid-phase pyrolysis of cured epoxy in solvent, and prepared Nd-Fe-B bonded magnets using the recycled powder. This paper reports the new technique for recycling Nd-Fe-B melt-spun powder and evaluates both magnetic properties of the bonded magnets prepared from recycled melt-spun powder and characteristics of a small motor using the recycled magnets.