United States

Coercivity of Sm2Fe17N3 as a sintered magnet has so far been only a few percent of the huge anisotropic magnetic field. Controlling grain boundary properties is a promising strategy to improve the coercivity. In powder metallurgical processes, coating raw powders with different materials can be a powerful methodology for grain boundary control. However, if the powder surface covered with the oxide film is coated, the coating phase and the magnetic phase do not contact with each other directly, so that a sufficient effect may not be obtained. Furthermore, iron oxides contained in the surface oxide film undergo a redox reaction with Sm2Fe17N3 at elevated temperatures, precipitating soft magnetic iron phase, which causes coercivity deterioration. For these reasons, the coating should be applied to surfaces without oxide film.

In this study, first we have established a versatile technique for coating powders with an oxide-free surface. By using the technique, we coated Sm2Fe17N3 powders with 20 non-magnetic metals, and investigated the effects on the coercivity. A simple heat treatment was applied to the coated powders instead of sintering, to clarify pure effects of coating excluding inter-grain coupling issues. 

Sm2Fe17N3 fine powders were prepared by jet-milling coarse powders. Coating was performed by arc-plasma deposition (APD) and DC magnetron sputtering. The powder was continuously stirred during deposition to ensure uniform coating. The whole process of the sample preparation was undertaken in a low-oxygen atmosphere. After the heat treatments, the sample powders were subjected to evaluations. Magnetic properties of the powders were measured as bonded magnets by using a vibrating sample magnetometer.

Scanning electron microscopy with energy dispersive X-ray spectrometry and X-ray photoelectron spectroscopy (XPS) suggested that an arc-plasma deposited Zn layer on Sm2Fe17N3 powder was highly uniform and had nearly 100 % coverage. Moreover, even the particles inside an agglomerate were fully coated with Zn, which suggested the agglomerates dynamically changed its constituent particles during the coating. 

An XPS depth-profile analysis confirmed that the powder had an oxide-free direct metal-metal interface between the coating layer and the main phase, in case of coating on a Sm2Fe17N3 powder prepared in the low-oxygen atmosphere. 

The effects of coating on the coercivity were evaluated first with Zn, Ti, and Al as the coating materials and both with APD and DC sputtering as the coating methods. With all the three coating metals, the sputter-coated powders showed higher coercivity than the raw powders. The APD powders had lower coercivity than the sputter-coated powders, and in the case of Ti, coercivity was even lower than that of the raw powder. Transmission electron microscopy and nano-beam electron diffraction suggested that the high energy particles deposited by APD damaged the magnetic phase. We therefore exclusively used the sputtering method for the rest of the experiments. 

It was found that sputter-coating as thick as several nm makes the coercivity increase, almost regardless of the coating element. However, further coercivity changes resulted from subsequent heat treatment at 500 °C depended strongly on the element. The mechanism of the former phenomenon is supposed to be a common and universal one. The latter one seems, on the other hand, to be related directly to the chemical details of each element. We are currently conducting research to clarify the factors controlling the coercivity change by coating and heat treatment.

REPM 2021: The 26th International Workshop on Rare-Earth and Future Permanent Magnets and their Applications

Coercivity Changes in Sm2Fe17N3 Powders by Direct Coating with Nonmagnetic Metals on Oxide-free Powder Surfaces

It is our great pleasure to invite you to attend the 26th International Workshop on Rare Earth and Future Permanent Magnets and Their Applications (REPM2021) which will be held virtually on June 7-10, 2021. Please note, this is an updated schedule due to COVID-19 travel restrictions which forced us to postpone the conference from summer of 2020. The REPM workshop takes place every two years and is the premier conference on permanent magnets covering a wide range of topics including:

* Rare earth magnets
* Rare earth-free magnets
* Raw materials, mining and recycling
* Advanced synthesis, processing and characterization techniques
* Theoretical modeling of coercivity
* Fundamental properties of advanced magnetic materials
* Thin film magnets
* Applications of permanent magnets

***Workshop***
The workshop will be chaired by Professor George C. Hadjipanayis, University of Delaware, Newark, DE and Dr. Jinfang Liu, President & COO of Electron Energy Corporation, Landisville, PA.
The objectives of the workshop are to bring together engineers and scientists who work on permanent magnets and their applications to present their latest results and exchange ideas on a wide range of relevant topics including resources, raw materials, recycling, processing, fundamental and hard magnetic properties and applications of rare earth and future magnets.

To regsiter for this event, please follow the link below.

technical paper

This paper investigates the viability of hydrogen decrepitation as a means for recovery and recycling of samarium cobalt (SmCo5) magnets. To hydrogen decrepitate SmCo5, a higher pressure is required compared to the atmospheric pressure used for NdFeB magnets, but it is essential to find the lowest energy route to make it economically viable. Samples of SmCo5 were characterised using scanning electron microscopy and X-ray diffraction (XRD), before using intelligent gravimetric analysis (IGA) to determine the hydrogen absorption plateau pressures at a range of temperatures. The samples were then subjected to a range of pressures from 5-20 bar, as well as a high temperature and pressure trial at 300 ⁰C and 20 bar, to find the conditions at which the magnets broke down into powders. IGA measurements showed that increasing the reaction temperature also increased the plateau pressure for absorption, and that the plateau pressure at room temperature was ~6 bar. Magnetised bulk samples of SmCo5, however did not react at this plateau pressure, instead requiring a minimum 10 pressure bar at room temperature over 24 hours, however they did not demagnetise. Recommendations were made to improve the viability of hydrogen decrepitation for recovery and recycling of SmCo5 magnets.


Recovery and Recycling of SmCo5 Using Hydrogen Decrepitation

This poster is on the use of the HPMS process (Hydorgen processing of magnet scrap) to liberate NdFeB alloy powders from water pumps, wind turbine magnets and loudspeakers. The separated powder has been subsequently processed into HDDR powders. The HDDR microstructures and magnetic properties are reported here.

HPMS Optimisation for End of Life NdFeB Containing Products

Phosphogypsum is a waste (or by-product) of phosphoric acid production [1]. This waste represents an economic potential thanks to a multitude of probable valuations such as rare earth recovery [2] that our SCIMATOP laboratory is interested in.
The rare earth content, the most effective extraction voice and the rate of their recovery are the main objectives of our study.
In the first step of our work, we focused simultaneously on the physic-chemical characterization of Moroccan phosphogypsum and the development of an optimal process for the solubilization of rare earths. the realization of this process required an experimental plan of 35 reactions where the treated phosphogypsum (drying + grinding + sieving) was exposed to acid attack by different percentages of sulfuric acid (from 10% up to 15%) by completing our experimental design, we were able to determine the total rare earth content contained in the Moroccan phosphogypsum and determine the rare earth recovery rate for each of the reactions carried out.
By analyzing the previous results, we have been able to deduce the optimal conditions for theleaching of rare earths by sulfuric acid (%H2SO4= 15%; T= 53 °C; S/L = 1/4, t = 40 min; A= 200 rpm.)
This work represents an essential stage of extraction of the rare earths by their solubilization and recovery in a liquid phase from which the final extraction step will take place.

References:

[1]: H. SFAR FELFOUL, P. CLASTRES, M. BEN OUEZDOU and A. CARLES-GIBERGUES (2002): Properties and prospects of phosphogypsum valorization (the example of Tunisia) Proceedings of International Symposium on Environmental Pollution Control and Waste Management 7-10 January 2002, Tunis (EPCOWM’2002), p.510-520

[2]: Fernando Pereira (2013): Phosphoric acid production by hydrochloric acid etching of phosphate ores with reduction of environmental pollution and recovery of rare earths as by-products. PhD thesis, Geochemistry. Mines National School of Saint-Etienne, French.


Optimization of Rare Earth Leaching from Phosphogypsum exposed to sulfuric acid attack

NdFeB magnet waste flows in the light of recycling – A detailed assessment

Abstract

The coercivity improvement in low-cost commercial heavy rare earth lean melt-spun Nd-Fe-B powders used for polymer-bonded magnets will be presented. We added low-temperature eutectic alloy Nd-Cu as diffusion source [1,2] to a powder with a composition that gives a very small proportion of the intergranular phase. With this addition and optimized procession parameters [3], we significantly increased the coercivity compared to the initial Nd-Fe-B powder. A commercial powder was mixed with a different amount (3 – 10 wt.%) of Nd70Cu30 powder. A mixture was annealed at different temperatures and times in a vacuum to optimize the annealing process and obtain maximum magnetic properties enhancement. After the optimized annealing treatment, the improved basic powder was mixed with polyphenylene sulphide polymer (PPS) in a weight ratio of 88:12, compressed in a press to get a green compact annealed at 300 °C for 40 min in vacuum to provide a polymer-bonded magnet [4].
For the polymer-bonded magnet, consisting of basic powder with the addition of only 3 wt.% of Nd70Cu30 powder, the coercivity increased from 745 kA/m to 855 kA/m. Meanwhile, the remanent magnetization decreased by only ≈ 6 % (from 0.51 T to 0.48 T). The microstructure characterization confirmed the diffusion and increasing proportion of Nd inside the Nd-Fe-B particles. In this way, we have shown that it is possible to improve commercial Nd-Fe-B magnetic powder's coercivity with a small addition of intergranular phase by diffusion of low-temperature eutectic alloy. The enhanced commercial magnetic powder's final result is a polymer-bonded magnet with enhanced coercivity, which is a significant step forward in the industrial production of low-cost polymer-bonded magnets [4].

[1] H. Sepehri-Amin et al., “High-coercivity ultrafine-grained anisotropic Nd-Fe-B magnets processed by hot deformation and the Nd-Cu grain boundary diffusion process,” Acta Mater., vol. 61, no. 17, pp. 6622–6634, 2013, doi: 10.1016/j.actamat.2013.07.049.
[2] T. G. Woodcock et al., “Atomic-scale features of phase boundaries in hot deformed Nd-Fe-Co-B-Ga magnets infiltrated with a Nd-Cu eutectic liquid,” Acta Mater., vol. 77, pp. 111–124, 2014, doi: 10.1016/j.actamat.2014.05.045. 
[3] M. Soderžnik, B. Ambrožič, K. Žagar Soderžnik, and M. Korent, “Limits of grain boundary engineering in nanocrystalline Nd-Fe-B melt-spun ribbons,” Mater. Lett., vol. 264, pp. 20–22, 2020, doi: 10.1016/j.matlet.2020.127338.
[4] M. Korent, et al. "A process for improving the magnetic properties of commercial Nd-Fe-B magnetic powder with a small proportion of intergranular phase and a process for producing polymer-bonded magnets from these magnetic powders", Patent submitted 25. January, 2021


The coercivity enhancement of melt-spun Nd-Fe-B magnetic powder by diffusion of low-temperature eutectic alloy for the purpose of manufacturing polymer-bonded magnets

We are investigating the novel possibilities and aspects of electrochemical recycling and reprocessing of Nd-Fe-(B)-based and Sm-Co magnets. First, we investigated the possibility of electrodeposition of Nd-Fe alloy at room T from ionic liquid based on 1-ethyl-3-methylimidizolium dicyanamide ([EMIM][DCA]) [1]. The electrodeposition of the rare earths (REs) at room T, is still a challenge because of their extremely low electrochemical potential. We observed that Nd(III) cannot be reduced independently, but it can be co-deposited with the addition of Fe(II). Further, we propose [2] a new concept of recycling the sintered (Dy,Nd)-Fe-B magnets selective electrochemical etching recovering the 2:14:1 matrix phase. Via an electrochemical etching method, we are able to recover pure individual 2:14:1 grains that can be re-used for new types of magnet production. Similar anodic etching was applied also for Sm-Co magnets, where it was shown, that it is possible to selectively etch the Sm, with simultaneous deposition of Co, Fe, and Cu on the cathode. With regards to the energy consumption of the new process, the proposed route is comparable to the established direct re-use methods like remelting and hydrogen processing of magnetic scrap. Further to tackle the issue of efficient and environmentally friendly rare earth recycling, we propose a novel electrochemical method for Nd–Fe–B PMs etching and REs recycling [3]. The proposed procedure enables complete electrochemical etching of the Nd–Fe–B magnet with further selective REs recovery and a simultaneous Fe metal deposition. The proposed procedure thus avoids the formation of solid Fe-based waste with the total re-use of the electrolyte resulting in no wastewater discharge.

Electrochemical Recycling and Reprocessing Aspects of Rare Earth-based Permanent Magnets

The emergence of contemporary processing techniques, like, for example, the additive manufacturing, makes a production of non-conventional-shape permanent magnets possible. The idea is to adjust the magnet geometry and magnetization in accordance with the prescribed resulting magnetic field as it follows from the design of the magnet-containing device. Although the relation between the magnetization and the field is described in terms of the classical electrodynamics, the solution of the problem is not straight forward due to the ill-conditioned respective equations. We will present the application of the adjoint method for eciently solving the inverse-magnetostatic problem by considering the abilities and limitations of the 3D-printing process.

Design of permanent magnets by solving the inverse magnetostatic problem

Effect of Mg layer on the crystal orientation and magnetic properties for FePt thin films

The recent trends in rare-earth usage and applications are discussed. Most of the motors of electric cars use Neodymium-iron-boron magnets, resulting in 1-2 kg of NdFeB magnets per vehicle. This can push significantly the demand for NdFeB magnets. Other application that may increase the demand of NdFeB magnets are giant off-shore wind turbines. The production of light rare-earths as neodymium and praseodymium can be easily increased. However, heavy rare-earths as terbium and dysprosium are scarce, and its price has increased significantly. Many Brazilian projects are stopped in present moment, waiting cheaper methods of rare-earth separation. However, Serra Verde project (state of Goias - Brazil) was scheduled to start in 2022. Recycling should be an economical activity. This explain why the recycling of rare-earths at the present time is very small. The recycling of rare-earths is estimated to be around 1% or less. The re-use of magnets is a possibility. This can be viable only since there is a standardization of manufactured magnets. 


Influence of grain size in the coercivity of sintered magnets

Abstract for REPM 2020
By: Jeff Green, President of J.A. Green & Company

For years the U.S. government adopted a hands-off approach to rare earths manufacturing, enabling foreign adversaries like China to dominate the industry and seek to exploit a U.S. dependency. U.S. policymakers have now fully recognized the threat of rare earths supply chain disruptions and are galvanized to confront this vulnerability head on. Both the past Administration and the current one are determined to push forward government policies and funding to support and grow the U.S. rare earth industry.

For the past few decades, Chinese-produced rare earths were the dominant or only source of rare earths in U.S. defense systems. In 2018, Congress addressed this vulnerability by including a provision within the National Defense Authorization Act that restricts the Defense Department from procuring neodymium-iron-boron (NdFeB) or samarium-cobalt (SmCo) magnets from China, Iran, Russia, and North Korea. The prohibition has had the intended effect of reducing the Defense Department’s reliance on China for rare earth magnets. Congress passed additional legislation in December that expanded this legislation to include other critical materials, demonstrating that lawmakers are prepared to continually respond to supply chain weaknesses where they exist. 

The White House has also done its part, issuing executive orders that empower the Defense Department and other agencies to assess gaps in the supply chain of critical materials, like rare earths. These assessments would later lead to the signing of five “Presidential Determinations,” authorizing up to $50 million in funding, to address the following issues within the critical materials supply chain: NdFeB magnet manufacturing; SmCo manufacturing; light rare earth separation; heavy rare earth separation; and metals and alloys manufacturing. The Defense Department has already awarded tens of millions of dollars to industry for solutions to all but two of these areas.

The next year should be promising for the rare earths industry, as members of Congress and the White House continue to spotlight the visibility of rare earths and seek solutions. However, the success of developing a long-term solution to U.S. rare earth needs ultimately depends on a policy-driven strategy that navigates institutional obstacles and leverages the political will of Congress and the Executive Branch. Jeff Green of J.A. Green & Company will present more details about the U.S. government’s latest actions in the rare earths sphere and will explain how domestic industry can partner with government to build a resilient supply of rare earths. 


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Next from REPM 2021: The 26th International Workshop on Rare-Earth and Future Permanent Magnets and their Applications

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Achievement of high coercivity in Sm-Fe-Ti-based powders

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