Hydrogen Absorption and Release Behavior in Hydrogen Decrepitation Process of Nd-Fe-B Alloys

The behavior of hydrogen absorption and release in hydrogen decrepitation (HD) process of Nd Fe B alloys were investigated. The results reveal that the reactivity and the amount of hydrogen absorption in HD process are related to the surface activity of the alloy so that the fresh and active surface has a higher efficiency. The presence of Nd rich phase at the grain boundary is an essential factor of the HD activity of the alloy at room temperature. On degassing, hydrogen is released from the HD powder continuously with increasing temperature. And the residual hydrogen is as low as 0 0015% at 1073 K, which shows that the hydrogen is almost exhaused. It is feasible to remove the hydrogen from the HD powder by heating treatment at the temperature of 523～723 K for 1 h prior to the magnetic field forming in order to decrease the harmful effect of hydrogen on the easy axis alignment of HD magnet.

Hydrogen Absorption of Nd-Fe-B Alloys

The technical parameters of HD process were studied, including the effects of temperature and neodymium contents on the incubation period of hydrogen absorption, hydrogen concentration and the rate of hydrogen absorbed. The results show that the incubation period is shortened and the rate of hydrogen absorbed is accelerated with rising temperature and surface area. These are attributed to the rising rate of hydrogen diffusion at higher temperature. The change of the incubation period and the rate of hydrogen absorbed have the similar trend resulted from the increasing content of the Nd-rich phase owing to the rising temperature. Moreover, the percent of the Nd-rich phase in the ingot can be calculated according to the total hydrogen weight gain.

Effect of HD Process on Microstructure and Hard Magnetic Properties of NdFeAlB Magnet

The effect of Hydrogen Decrepitation (HD) process on the magnetic properties and microstructure of sintered NdFeAlB magnet (HD magnet) was investigated. The results show that the coercivity of HD magnet is higher than that of traditional ball milling (BM) magnet, while the remanence and the maximum energy product of HD magnet are lower. Microstructure analysis shows that some fine un sintered powders are distributed at the grain boundaries of HD magnet. X ray diffraction (XRD) analysis reveals that the degree of easy axis alignment of HD magnet is lower. Some ideas to improve the current HD process were proposed.

HD Processes in the Production of SmCo_5 Permanent Magnets

The application of ‘extreme’ hydrogen-decrepitation (HD) process using high-pressure disproportionation was extended to Sm-Co5-type-alloy. The alloy with nominal composition of Sm36Co64 was treated under 1.0～2.0 MPa H2 pressure for several hours at room temperature for decrepitation. After disproportionation were high hydrogen pressures, the bulk alloys were disproportionated into particles with a size of 200. Investigations by powder X-ray diffractometer (XRD) showed, the after HD sample crystallized in the hexagonal CaCu5-type structure. The temperature dependence of pressure analysis (TPA) curve of the SmCo5 alloy showed that the hydrogen absorption temperature was about 150 ℃. Cylindrical sintered magnets of composition Sm36Co64 were prepared using HD ball milled, isostatic pressing, vacuum sintering and subsequent heat treatment. The demagnetization curves showed that the HD processes could improve the magnetic properties and squareness factor of the SmCo5 sintered magnet.

A Systematic Classification and Labelling Approach to Support a Circular Economy Ecosystem for NdFeB-Type Magnet

Availability of magnetic materials is most crucial for modern Europe,as they are integral to energy conversion across the renewable energy and electric mobility sectors.Unfortunately,there is still no circular economy to reuse and capture value for these types of materials.With the prediction that the need for NdFeB Rare Earth(RE)magnets will double in the next 10 years,this problem becomes even more urgent.As the quality of the recollected materials varies significantly,the development of a classification system for recyclate grades of EOL NdFeB magnets in combination with an eco-labelling system for newly produced RE permanent magnets is proposed to clearly identify different magnet types and qualities.It categorises the NdFeB magnets by technical pre-processing requirements,facilitating use of the highly effective HPMS process(Hydrogen Processing of Magnetic Scrap)for re-processing extracted materials directly from NdFeB alloy.The proposed measures will have a great impact to overcome existing low recycling rates due to poor collection,high leakages of collected materials into non-suitable channels,and inappropriate interface management between logistics,mechanical pre-processing and metallurgical metals recovery.

Regeneration of waste sintered Nd-Fe-B magnets to fabricate anisotropic bonded magnets

The waste sintered Nd-Fe-B magnets were regenerated as magnetic powders via manually crushing （MC） or hydrogen decrepitation （HD） to fabricate anisotropic bonded magnets. Effect of size distribution on the magnetic properties of the regenerated magnetic MC and HD powders was investigated. For the MC powders, as the particle size decreased, the remanence （Br） increased first, and then decreased again, while the coercivity （Hci） dropped monotonically. The powders with particle size in the range of 200-450μm possessed the best magnetic properties ofBr of 1.22 T and Hci of 875.6 kAJm. The corresponding bonded magnet exhibited magnetic properties ofBr of 0.838 T, Hci of 940.9 kA/m, and （BH）max of 91.4 kJ/m^3, respectively. On the other hand, the liD powders with particle size range of 200-450 μm bore the best magnetic properties Of Br of 1.24 T and Hci of 860.4 kA/m. Compared with magnetic properties of the waste magnet, the powders retained 93.9% of Br and 70.0% of Hci, respectively. The bonded magnet produced from HD powders possessed Br of 0.9 T, Hci of 841.4 kA/m, and （BH）max of 111.6 kJ/m^3, indicating its good potential in practical applications.