ABSTRACT
In this review article, we focus on the relationship between permanent magnets and the electric motor, as this relationship has not been covered in a review paper before. With the increasing focus on battery research, other parts of the electric system have been neglected. To make electrification a smooth transition, as has been promised by governing bodies, we need to understand and improve the electric motor and its main component, the magnet. Today's review papers cover only the engineering perspective of the electric motor or the material-science perspective of the magnetic material, but not both together, which is a crucial part of understanding the needs of electric-motor design and the possibilities that a magnet can give them. We review the road that leads to today's state-of-the-art in electric motors and magnet design and give possible future roads to tackle the obstacles ahead and reach the goals of a fully electric transportation system. With new technologies now available, like additive manufacturing and artificial intelligence, electric motor designers have not yet exploited the possibilities the new freedom of design brings. New out-of-the-box designs will have to emerge to realize the full potential of the new technology. We also focus on the rare-earth crisis and how future price fluctuations can be avoided. Recycling plays a huge role in this, and developing a self-sustained circular economy will be critical, but the road to it is still very steep, as ongoing projects show.
ABSTRACT
The green transition initiatives and exploitation of renewable energy sources require the sustainable development of rare earth (RE)-based permanent magnets prominent technologies like wind turbine generators and electric vehicles. The recycling of RE-based permanent magnets is necessary for the future supply of critical rare-earth elements. The short-loop recycling strategies to directly reprocess Nd-Fe-B magnet waste are economically attractive and practical alternatives to conventional hydro- and pyrometallurgical processes. This study focuses on the development of a procedure to extract the (Nd, Pr)2Fe14B hard-magnetic phase from sintered Nd-Fe-B magnets. The extraction is achieved through preferential chemical leaching of the secondary, RE-rich phases using 1 M citric acid. Before the acid treatment, the magnets were pulverized through hydrogen decrepitation (HD) to increase the material's surface-to-volume ratio. The as-pulverized Nd-Fe-B powder was subsequently exposed to a 1 M citric acid solution. The effect of leaching time (5-120 min) on the phase composition and magnetic properties was studied. The results of the microstructural (SEM) and compositional (ICP-MS) analyses and the study of thermal degassing profiles revealed that the RE-rich phase is preferentially leached within 5-15 min of reaction time. Leaching of the secondary phases from the magnet's multi-phase microstructure is governed by the negative electrochemical potential of Nd and Pr. The extraction of (Nd, Pr)2Fe14B grains by the proposed acid leaching approach is compatible with the existing hydrogen processing of magnetic scrap (HPMS) technologies. The use of mild organic acid as a leaching medium makes the leaching process environmentally friendly, as the leaching medium can be easily neutralized after the reaction is completed.
ABSTRACT
The green transition initiative has exposed the importance of effective recycling of Nd-Fe-B magnets for achieving sustainability and foreign independence. In this study, we considered strip-cast, hydrogenated, jet-milled Nd-Fe-B powder as a case study to explore the potential for selective chemical leaching of the Nd-rich phase, aiming to extract the Nd2Fe14B matrix phase. Diluted citric and nitric acids at concentrations of 0.01, 0.1, and 1 M were considered potential leaching mediums, and the leaching time was 15 min. Microstructural investigation, magnetic characterization, and elemental compositional analysis were performed to investigate leaching efficiency and selectivity. Based on SEM analysis, Nd/Fe ratio monitoring via ICP-MS, and the high moment/mass value at 160 emu/g for the sample leached with 1 M citric acid, 1 M citric acid proved highly selective toward the Nd-rich phase. Exposure to nitric acid resulted in a structurally damaged Nd2Fe14B matrix phase and severely diminished moment/mass value at 96.2 emu/g, thus making the nitric acid unsuitable for selective leaching. The presence of hydrogen introduced into the material via the hydrogen decrepitation process did not notably influence the leaching dynamics. The proposed leaching process based on mild organic acids is environmentally friendly and can be scaled up and adopted for reprocessing industrial scrap or end-of-life Nd-Fe-B magnets to obtain single-phase Nd-Fe-B powders that can be used for novel magnet-making.
ABSTRACT
Simple, low-cost methods for sensing volatile organic compounds that leave no trace and do not have a detrimental effect on the environment are able to protect communities from the impacts of contaminants in water supplies. This paper reports the development of a portable, autonomous, Internet of Things (IoT) electrochemical sensor for detecting formaldehyde in tap water. The sensor is assembled from electronics, i.e., a custom-designed sensor platform and developed HCHO detection system based on Ni(OH)2-Ni nanowires (NWs) and synthetic-paper-based, screen-printed electrodes (pSPEs). The sensor platform, consisting of the IoT technology, a Wi-Fi communication system, and a miniaturized potentiostat can be easily connected to the Ni(OH)2-Ni NWs and pSPEs via a three-terminal electrode. The custom-made sensor, which has a detection capability of 0.8 µM/24 ppb, was tested for an amperometric determination of the HCHO in deionized (DI) and tap-water-based alkaline electrolytes. This promising concept of an electrochemical IoT sensor that is easy to operate, rapid, and affordable (it is considerably cheaper than any lab-grade potentiostat) could lead to the straightforward detection of HCHO in tap water.
