Hydrogenation, Disproportionation, Desorption And Recombination Research Articles

Evolución y proceso de fabricación de imanes “NEO” aplicados a motores de vehículos eléctricos

Tras el desarrollo de los imanes Nd-Fe-B o “Neo”, éstos son ahora componentes esenciales en muchos campos de la tecnología debido a su capacidad para proporcionar un fuerte flujo magnético. Existen dos técnicas bien establecidas para la fabricación de imanes de tierras raras: a) el uso de la metalurgia de polvo para obtener cuerpos magnéticos de alto rendimiento, anisotrópicos, totalmente densos; y b) el proceso de hilado por fusión o HDDR (hidrogenación, decrepitación, desorción y recombinación) se usa ampliamente para producir polvos magnéticos para imanes aglomerados. En la industria de los imanes de Nd-Fe-B sinterizados, la producción total ha aumentado y su aplicación dominante es principalmente motores y en particular, su uso para automóviles híbridos es una de las aplicaciones más atractivas. También se han utilizado imanes aglomerados para motores pequeños, los estudios de nanocompuestos y de imanes Sm-Fe-N se han generalizado. Este artículo revisa el estado actual y las tendencias futuras en la investigación de imanes permanentes.

Supercapacitor Application of Powder Prepared Using the Hydrogenation Disproportionation Desorption and Recombination (HDDR) Process in Graphene Oxide

Graphene (G) has been attracted great interest for its excellent electrical properties. However, the large-scale production of graphene is presently unfeasible. Graphene oxide (GO) can be (partly) reduced to graphene-like sheets by removing the oxygen-containing groups with the recovery of a conjugated structure. It can be produced using inexpensive graphite as raw material by cost-effective chemical methods. Although hydrogen (mixed with argon) at high temperature (1100°C) has been employed to reduce GO powder, the hydrogenation disproportionation desorption and recombination (HDDR) process in particular was unreported for this purpose. In the present work, attempts of reducing GO powder using the HDDR process have been carried out and investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR). The experimental results of processing graphene oxide powder using unmixed hydrogen at moderate temperatures (about 850°C) and relatively low pressures (<2 bars) have been reported.

A systematic study of HDDR processing conditions for the recycling of end-of-life Nd-Fe-B magnets

Scrap rare earth permanent magnets from various sources and applications were collected and processed for recycling using hydrogen decrepitation (HD) and hydrogenation disproportionation desorption and recombination (HDDR) processes. The effects of the principle HDDR processing parameters hydrogen pressure, hydrogen desorption rate and temperatures on the magnetic properties of the recycled materials have been investigated systematically. The optimum hydrogen pressures required for the complete disproportionation of the various magnet compositions were determined. We found that a hydrogen heat treatment composed of two steps (780 °C and 840 °C) and a moderate desorption rate can be used for the magnets having a higher Dy and Co content to obtain high quality anisotropic HDDR powders for resin bonded magnet production.

Structure and Properties of Nd-Fe-B Alloy Subjected to HDDR Process

In this paper the Hydrogenation, Disproportionation, Desorption and Recombination (HDDR) route was tested, for the Nd-Fe-B master alloy, as a prospective procedure for recycling of sintered scrap neodymium magnets. The HDDR method is based on the hydrogen induced reversal phase transformation of Nd-Fe-B alloy: Nd2Fe14B + (2±x) H2 = 2NdH2±x + Fe2B + 12Fe. Microstructural observations (SEM), phase constitution studies (XRD) and measurement of magnetic properties (VSM) were done to investigate the HDDR transformation progress. It was observed that disproportionation reaction starts at the grain boundaries, where the Nd-rich phase is located. Average grain size was reduced and coercive material was produced as a result of the HDDR process. Obtained results are similar to literature data.

High-temperature magnetic properties of anisotropic MnBi/NdFeB hybrid bonded magnets

Anisotropic MnBi/NdFeB (MnBi contents of 0 wt%, 20 wt%, 40 wt%, 60 wt%, 80 wt%, and 100 wt%) hybrid bonded magnets were prepared by molding compression using MnBi powders and commercial hydrogenation disproportionation desorption and recombination (HDDR) NdFeB powders. Magnetic measurements at room temperature show that with MnBi content increasing, the magnetic properties of the MnBi/NdFeB hybrid bonded magnets all decrease gradually, while the density of the hybrid magnets improves almost linearly. In a temperature range of 293–398 K, the coercivity temperature coefficient of the hybrid magnets improves gradually from −0.59 %·K−1 for the pure NdFeB bonded magnet to −0.32 %·K−1 for the hybrid bonded magnet with 80 wt% MnBi, and the pure MnBi bonded magnet exhibits a positive coercivity temperature coefficient of 0.61 %·K−1.

The development of microstructure during hydrogenation–disproportionation–desorption–recombination treatment of sintered neodymium-iron-boron-type magnets

The hydrogen absorption and desorption characteristics of the hydrogenation disproportionation desorption and recombination (HDDR) process on scrap sintered neodymium-iron-boron (NdFeB) type magnets have been investigated. At each stage of the process, the microstructural changes have been studied using high resolution scanning electron microscopy. It was found that the disproportionation reaction initiates at grain boundaries and triple points and then propagates towards the centre of the matrix grains. This process was accelerated at particle surfaces and at free surfaces produced by any cracks in the powder particles. However, the recombination reaction appeared to initiate randomly throughout the particles with no apparent preference for particle surfaces or internal cracks. During the hydrogenation of the grain boundaries and triple junctions, the disproportionation reaction was, however, affected by the much higher oxygen content of the sintered NdFeB compared with that of the as-cast NdFeB alloys. Throughout the entire HDDR reaction the oxidised triple junctions (from the sintered structure) remained unreacted and hence, remained in their original form in the fine recombined microstructure. This resulted in a very significant reduction in the proportion of cavitation in the final microstructure and this could lend to improved consolidation in the recycled magnets.

Origin of Poor Thermal Stability of HDDR-Treated Nd-Fe-B-Type Material

Thermal stability of the Nd12.5Fe80.6B6.4Ga0.3Nb0.2 hydrogenation, disproportionation, desorption and recombination (HDDR)-treated powder was studied, and it was correlated to the residual hydrogen in the powder. Presence of the residual hydrogen in the HDDR-treated powder was investigated by X-ray diffraction (XRD), thermopiezic analyser (TPA) and hydrogen analysis. The HDDR-treated material contained a significant amount of hydrogen, and it influenced the thermal stability of the material. Coercivity of the HDDR-treated powder was markedly reduced by heating above 600 °C, and it was related to the residual hydrogen. The residual hydrogen existed in the form of Nd2Fe14BHx hydride, and it was disproportionated into α-Fe, Fe2B and NdH2 phases at an elevated temperature. The coercivity reduction was attributed to the magnetically soft α-Fe and Fe2B phases formed by the disproportionation.

ChemInform Abstract: Current Status and Recent Topics of Rare‐Earth Permanent Magnets

AbstractReview: 80 refs.

Local orientation analysis by electron backscatter diffraction in highly textured sintered, die-upset, and hydrogenation disproportionation desorption and recombination Nd–Fe–B magnets

Local texture in polycrystalline Nd–Fe–B powders produced by hydrogenation disproportionation desorption and recombination (HDDR) and by pulverization of hot deformed material (MQA-F) has been studied by electron backscatter diffraction and compared with the ideal case of a powder consisting of single-crystalline particles. The HDDR powder particles exhibited a biaxial {001}, 〈100〉 local texture, whereas the MQA-F particles showed a local 〈001〉 fiber texture. This was explained by differences in the texture mechanisms of the two materials. Resin bonded compacts were prepared from the two polycrystalline powders following alignment in an external magnetic field. The degree of texture on the global scale was determined from magnetic measurements of these compacts and the results were compared with those from a commercial Nd–Fe–B sintered magnet and hot deformed magnet.

Current status and recent topics of rare-earth permanent magnets

After the development of Nd–Fe–B magnets, rare-earth magnets are now essential components in many fields of technology, because of their ability to provide a strong magnetic flux. There are two, well-established techniques for the manufacture of rare earth magnets: powder metallurgy is used to obtain high-performance, anisotropic, fully dense magnet bodies; and the melt-spinning or HDDR (hydrogenation, disproportionation, desorption and recombination) process is widely used to produce magnet powders for bonded magnets. In the industry of sintered Nd–Fe–B magnets, the total amount of production has increased and their dominant application has been changed to motors. In particular, their use for motors in hybrid cars is one of the most attractive applications. Bonded magnets have also been used for small motors, and the studies of nanocomposite and Sm–Fe–N magnets have become widespread. This paper reviews the current status and future trend in the research of permanent magnets.

Comparison of local and global texture in HDDR processed Nd–Fe–B magnets

The local texture in polycrystalline Nd–Fe–B powder particles processed by hydrogenation disproportionation desorption and recombination (HDDR) has, for the first time, been observed directly by electron backscatter diffraction (EBSD). The local texture quality was found to vary strongly with the hydrogen pressure applied during HDDR processing. At 0.3 bar, a strong biaxial local texture occurs in the individual powder particles. Increasing the hydrogen pressure during HDDR results initially in a lower texture quality and finally leads to near-isotropic particles. Clusters of similarly oriented grains within near-isotropic particles were observed rather than a completely random spatial distribution of orientations. The local texture within the powder particles was shown to be critical in determining the magnetic properties of compacts produced by aligning the powder in an external magnetic field. A compact produced from the powder with the strongest local texture (processed at 0.3 bar) showed highly anisotropic magnetic properties with remanence (related to the density of Nd 2Fe 14B) parallel and perpendicular to the applied field direction of 1.24 T and 0.55 T, respectively.

ChemInform Abstract: Hydrogenation Disproportionation Desorption Recombination Processes Applied to NdFeB-, SmFe- and SmCo-Type Alloys

Recent aspects of hydrogenation disproportionation desorption and recombination (HDDR) phenomena in NdFeB-, SmFe- and SmCo-type alloys are reviewed in this paper. The effects of additives on hydrogen sorption and magnetic properties are discussed. The possibilities of producing magnetically anisotropic NdFeB HDDR magnets by hot deformation or alternatively pre-aligning and compacting anisotropic powders are described. Current models for the inducement of magnetic anisotropy in NdFeB HDDR powder are summarized and it is shown that anisotropic powder can be produced from a ternary compound when using a modified processing route. The application of ‘extreme’ hydrogenation conditions, namely high hydrogen pressure or reactive milling in a hydrogen atmosphere at enhanced temperatures, allows the disproportionation of thermodynamically very stable compounds such as Sm2Fe17−xGax (x≥l), SmCo5 or Sm2Co17. Reactive milling and subsequent recombination in vacuum lead to structures, of both the disproportionated and the recombined type, which are on a remarkably finer scale than those commonly observed for standard HDDR procedures. Exchange coupling between the nano-scaled grains can result in magnetically single phase behavior despite a multiphase microstructure and in particular for the Sm2Co17 alloy, a remanence enhancement was observed after recombination at temperatures ≤700°C.

ChemInform Abstract: The Influence of Alloying Additions and Process Parameters on the Magnetic Properties of PrFeB-Based Bonded Magnets.

Abstract The effects of Co, Zr, Nb, Ga and Dy additions upon the magnetic properties of PrFeB-based alloys have been studied. Bonded magnets have been prepared from as-cast and homogenised alloys using an optimised hydrogenation disproportionation desorption and recombination (HDDR) process. In general, the HDDR bonded magnets from homogenised alloys exhibited higher remanence (Br), squareness factor (SF) and intrinsic coercivity (iHc). In particular, the Pr13.7Fe63.5Co16.7B6Nb0.1 HDDR magnet exhibited the best overall magnetic properties (Br=1032±20 mT, iHc=793±20 kA/m and SF=0.51), indicating that Co and Nb additions, in these proportions have a beneficial effect on PrFeB-based magnets. Conversely, additions of Ga and Dy were observed to dramatically reduce the intrinsic coercivity of Pr-based HDDR magnets.

Dependence of magnetic properties of HDDR Nd-Fe-B bonded magnet on intergranular phase

Using proposed different anisotropy expressions K 1′(r) and K 1″(r) at the grain boundary, we investigate the effect of intergranular phase (IP) on the average anisotropy 〈K 1〉 of grain boundary and the coercivity H c of HDDR (hydrogenation, disproportionation, desorption and recombination) Nd-Fe-B bonded magnet. The results indicate that when the IP’s thickness d is zero, 〈K 1〉 and H c based on K 1′(r) are equal to the corresponding ones based on K 1″(r). While d takes nonzero values, 〈K 1〉 and H c based on K 1″(r) falls and rises more rapidly, respectively, with increasing d. When d is 1 nm and the structure defect thickness r 0 is close to the thickness of domain wall (∼4 nm), the calculated coercivity is consistent well with the avaiable experimental data.

Effect of Al and Zn additives on grain size of Mg-3Ni-2MnO 2 alloy

The effect of Al and Zn additives on the grain size of Mg-3Ni-2MnO 2 alloy was investigated. The nanostructured Mg-3Ni-2MnO 2 and Mg-3Ni-2MnO 2-3Al-Zn were made by ball milling process under hydrogen atmosphere. The XRD results and TEM analysis reveal that Al and Zn additives almost have no effect on the grain size of Mg-3Ni-2MnO 2 alloy. The present study provides us a feasibility of producing nano-structured magnesium alloys, based on hydrogenation, disproportionation, desorption and recombination(HDDR), by adding beneficial elements to hydrogen storage materials.

X-Ray Diffraction Analysis and Magnetic Properties of Pr-Fe-B HDDR Powders and Magnets

Fine magnetic powder has been produced using the hydrogenation disproportionation desorption and recombination (HDDR) process. The first goal of this work involved an investigation of a range of disproportionation/desorption temperatures between 800 and 900°C with the purpose of optimizing the HDDR treatment for a Pr14Fe80B6 alloy. The cast alloy was annealed at 1100°C for 20 hours for homogenization. The optimum disproportionation temperature for achieving high anisotropy was 820°C. The influence of the reaction temperature on the microstructure and magnetic properties of Pr14Fe80B6 HDDR powders and magnets has been shown. A second stage of this study involved the characterization, for each temperature, of the HDDR processed powder using X-ray diffraction analysis. Samples of the HDDR material have been studied by synchrotron radiation powder diffraction using the Rietveld method for cell refinement, phase quantification and crystallite sizes determination. Scanning electron microscopy (SEM) has also been employed to reveal the morphology of the HDDR powder.

Improvement of microstructure and magnetic properties of Nd–Fe–B alloys by Nb and Co additions

In order to establish the role of niobium on the hydrogenation, disproportionation, desorption and recombination (HDDR) behavior of near-stoichiometric alloys, two alloys: NdI3Fe8OB7 and Nd13Fe78Nb1Co1B7 (at%) were investigated before, during and after the HDDR process. The microstructure of the as-cast Nb-free alloy before employing the HDDR process was found to consist of three phases, the matrix Nd 2Fe 14B (φ) phase, Nd-rich phase and a significant amount of free iron; whereas, the microstructure of the Nb-containing alloy consisted of only the first two phases. The HDDR behavior of the above alloys was characterized using a high-resolution scanning electron microscope (HRSEM). The disproportionation of the Nd 2Fe 14B (φ) matrix phase starts at the Nd-rich/φ phase interface, resulting in the formation of a sub-micron structure consisting of Fe, Fe 2B and Nd-hydride. The disproportionated structures of the Nb-free alloy contained large arms of free iron dendrites, which were retained from the as-cast structures. In the niobium-containing alloy, the recombined grains appear finer and with more rounded shapes in comparison with those of the NdFeB alloy. Promising magnetic properties have been obtained for bonded magnets using the HDDR powder. The magnetic properties, especially the intrinsic coercivity, improved significantly by using ∼1% Nd in excess of the stoichiometric content.

Magnetic properties of Pr-Fe-Co-B bonded HDDR magnets with alloying additions

Microstructures and magnetic properties of Pr-Fe-Co-B bonded magnets were investigated. The magnets can be represented by the formulae, Pr14Fe63.9Co16B6M 0.1 (M = Ti, V, Cr, Ni, Zr, Nb or Mo), Pr14Fe63.8Co16B6Nb 0.1T0.1 (T/= Al, Si, P, Cu or Ga) and Pr14Fe63.6Co16B6Nb 0.1R0.3 (R = Gd, Tb or Dy). The effects of additions on the magnetic properties of PrFeCoB-based magnets have been studied. Magnetically hard powders have been produced from homogenised alloys using the hydrogenation, disproportionation, desorption and recombination (HDDR) process. The HDDR powders were isostatically pressed and bonded with cyanoacrylate adhesive to form permanent magnets.

The Influence of Al, Cu and P Content on the Magnetic Properties of PrFeCoBNb-Based HDDR Magnets

This paper reports the results of investigations carried out to determine the magnetic properties of some praseodymium-based magnets represented by the formula Pr14Fe63.9-xCo16B6Nb0.1Mx. Bonded magnets of various compositions were prepared from annealed alloys using the hydrogenation, disproportionation, desorption and recombination (HDDR) process. The HDDR powders were isostatically pressed and bonded with cyanoacrylate adhesive to form permanent magnets. The effect of the addition element content on the magnetic properties of these magnets was investigated. The amount of Al, Cu and P addition has a significant effect on the magnetic behavior of these magnets. Under the present processing condition 0.3 at%Al enhanced the intrinsic coercivity to 1.27 and a minimal amount of P improved the remanence to 0.77 T. Copper addition was deleterious to the magnetic properties of the HDDR bonded magnets, independently on the content added.

The Influence of Si, Ga and Gd Content on the Magnetic Properties of Pr-Fe-Co-B-Nb HDDR Bonded Magnets

This paper reports the results of investigations carried out to determine the microstructure and magnetic properties of some praseodymium-based magnets represented by the formula Pr14Fe63.9-xCo16B6Nb0.1Mx. Bonded magnets were prepared the annealed alloys using the hydrogenation, disproportionation, desorption and recombination (HDDR) process. The HDDR powders were isostatically pressed and bonded with cyanoacrylate adhesive to form permanent magnets. The effect of addition element content on the magnetic properties of these magnets was investigated. The amount of addition has a significant effect on the magnetic behaviour of these bonded magnets.