Hydrogenation, Disproportionation, Desorption And Recombination Process 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.

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.

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

AbstractReview: 80 refs.

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.

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.

The effects of carbon substitution on the behavior of hydrogen in Nd–Fe–B-type magnetic alloys

In the present study, the hydrogen absorption and desorption behavior of Nd–Fe–B-type alloys with the substitution of carbon for boron was investigated focusing on the disproportionation and recombination reaction of the hydrogenation, disproportionation, desorption and recombination (HDDR) process. Furthermore, the HDDR treatment of carbon-substituted Nd–Fe–B alloy was carried out. It was found that the most distinct effect of carbon substitution for boron in Nd–Fe–B-type alloy is the lowering of the starting temperature of disproportionation reaction in the HDDR process. The HDDR-treated Nd 12.6Fe bal.Co 11.6Ga 1.0Zr 0.1B 4.0C 2.0 powder shows better magnetic properties than the Nd 12.6Fe bal.Co 11.6Ga 1.0Zr 0.1B 6.0 powder at short disproportionation reaction time. This may be due to the rapid disproportionation of Nd 2Fe 14(B,C) phase at the disproportionation reaction temperature.

Ga site occupancy in HDDR-treated Nd2Fe14B-based alloy by XAFS

Abstract The changes of local structure for Ga in Nd 13.0 Fe 68.2 Co 10.8 Ga 1.0 Zr 0.1 B 6.9 during hydrogenation, disproportionation, desorption and recombination (HDDR) process are studied by fluorescence XAFS in order to understand the evolution of magnetic anisotropy by HDDR process. Comparing the observed Ga XAFS data with the calculated ones, using ab initio calculation (FEFF), Ga is proved to occupy preferentially an Fe(c) site in the Nd 2 Fe 14 B structure before disproportionation and dissolves in α-Fe after the disproportionation. In the recombined state Ga redistributes into two phases, i.e. Nd 2 Fe 14 B and a Nd-rich phase. The behavior of Ga during the HDDR process differs from Zr which occupies Fe(j 2 ) sites before disproportionation and after the disproportionation.

The HD and HDDR processes in the production of Nd-Fe-B permanent magnets

This paper describes work done on an EC-funded project to develop and scale up the hydrogenation, disproportionation, desorption and recombination (HDDR) process. The hydrogen decrepitation (HD) and HDDR processes are summarized together with earlier work showing that the HD process has considerable economic advantages and the recombination stage of the HDDR process is critical, but that it may be separated from the disproportionation stage. Holding the material for extended times in the disproportionated state increases the coercivity of the HDDR material and this improvement tails off exponentially with time. It is also shown that raising the temperature during disproportionation improves the loop shape and remanence of the HDDR material whilst reducing the hydrogen pressure during disproportionation reduces the time dependence of the reaction, allowing much shorter processing times.

Fundamental and practical aspects of the hydrogenation, disproportionation, desorption and recombination process

In this paper, fundamental and practical aspects of the hydrogenation, disproportionation, desorption and recombination (HDDR) process in Nd - Fe - B-type alloys are reviewed. Thermodynamic aspects of the process are discussed as well as the microstructural changes throughout the different stages of the process. A detailed study of the disproportionated state is presented with particular reference to the role of the grain boundary phases. The effect of additives such as Co, Ga and Zr on the general hydrogen absorption and desorption behaviour of the matrix phase and their role in the inducement of magnetic anisotropy in the HDDR powder is discussed. Various mechanisms which have been suggested to explain the origin of anisotropy are described. Finally, consideration is given to some of the problems associated with the `scaling-up' of the HDDR process, which appears to be an extremely promising method for the production of bonded or fully dense hot-pressed magnets.

HDDR behaviour of Nb-containing NdFeB near-stoichiometric alloys

The hydrogenation, disproportionation, desorption and recombination (HDDR) behaviours of Nd 11.8Fe 82.3− x Nb x B 5.9 ( x = 0, 1, 2, 3, 5 at.%) alloys were studied by differential thermal analysis. Microstructural and hydrogen absorption/desorption studies were conducted prior to, during and after the HDDR process in order to establish the relationships between the initial microstructure and the changes in the HDDR behaviour and to compare with NdFeB-type alloys without additions. Niobium additions resulted in the formation of Nb 26Fe 32B 42 and Nd 2Fe 17. The area of the disproportionation peak was found to diminish with increasing Nb content in the alloy; this was ascribed to the increasing amounts of Nd-rich material and Nb 26Fe 32B 42 phase which did not disproportionate. The presence of Nd-rich material was indicated by the hydrogen desorption behaviour of the disproportionated alloys. The HDDR behaviour of Nd 11.8Fe 82.3− x Nb x B 5.9 ( x = 2, 5) alloys was investigated using a high resolution scanning electron microscope. The disproportionation of the Nd 2Fe 14B (Φ) matrix phase starts at the grain boundary and at the interface of the Nb 26Fe 32B 42-Φ phases, resulting in the formation of a submicrometre structure consisting of Fe, Fe 2B and Nd-hydride. The HDDR process proved to be a very rapid and efficient method of homogenising the as-cast alloys.

Preparation of nanocrystalline TiAl powder by the HDDR process using mechanical grinding in a hydrogen atmosphere

Titanium aluminides (TiAl and Ti[sub 3]Al) are potential high temperature structural materials for aerospace applications owing to their low density, high specific strength and oxidation and corrosion resistance. However, their low ductility at room temperature prevents their use and efforts are being made to increase ductility by alloying additions, grain refinement, the heat treatment to change the microstructures and so on. However, these efforts have had only limited success. Generally, the grain refinement is a useful technique to enhance ductility of metallic materials. Recently, it has been demonstrated that the coarse-grained materials are converted into very fine grained powder by the HDDR (hydrogenation, disproportionation, desorption and recombination) process in the Nd-Fe-B permanent magnets. The first step of the HDDR process is the decomposition of the intermetallic compound A[sub 1[minus]x]B[sub x], where A and B is a hydride forming and non-forming metal respectively, into hydride AH[sub x] and the other B-rich A[sub 1[minus]x[minus]y]B[sub x] compound (or pure metal B) by hydrogenation. The second step is realloying between A, produced by the decomposition of AH[sub x], and the B-rich A[sub 1[minus]x[minus]y]B[sub x] compound. TiAl consists of hydride forming metal (Ti) and hydride non-forming metals (Al), but it does not absorb hydrogen andmore » does not decompose into TiH[sub 2] and the Al-rich TiAl. Consequently, the grain refinement by the conventional HDDR process is impossible in the case of TiAl. In the present work, the authors try to refine the grain size of TiAl by the modified HDDR process using mechanical grinding (MG) in a hydrogen atmosphere.« less