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Relationship between Nd-rich phase and oxygen content for additive-free sintering with regenerated powder from magnet sludge waste

2026-01-31T15:00:00Z

Title: Relationship between Nd-rich phase and oxygen content for additive-free sintering with regenerated powder from magnet sludge waste Author(s): Galkin, Vitalii; Kim, Jeongmin; Roh, Jong Wook; Kim, Dongsoo Abstract: Recycling of Nd-Fe-B magnet sludge into high-performance powders is critical for sustainable rare-earth resource utilization. In this study, Nd-Fe-B powders were regenerated via a reduction-diffusion process and subjected to different washing treatments to investigate their effects on microstructure, phase composition, and magnetic properties. Conventional water washing at larger scales resulted in increased oxidation, depletion of Nd-rich phase, while requiring prolonged washing cycles and excessive water consumption. In contrast, scale up washing with an NH4NO3 solution in methanol effectively minimized oxidation, preserved Nd-rich, and maintained a uniform 1–2μm particle size distribution. The resulting powders exhibited superior magnetic properties, including high coercivity, enhanced squareness, and an improved maximum energy product. The NH4NO3 in MeOH washing method also demonstrated higher yield, improved processing efficiency, and scalability, highlighting its potential as a practical approach for sustainable production of regenerated Nd-Fe-B powders. These findings provide a promising pathway for recycling magnet sludge into high-quality powders suitable for sintered magnet fabrication, contributing to resource conservation and the advancement of rare-earth recycling technologies.

Low-temperature and low-pressure sinter-bonding for thermoelectric generator devices using Cu nanoparticle paste

2026-01-31T15:00:00Z

Title: Low-temperature and low-pressure sinter-bonding for thermoelectric generator devices using Cu nanoparticle paste Author(s): Chung, Seok-Hwan; Park, Jong Ho; Kim, Jong Tae; Kim, Jeongmin; Kim, Dong Hwan Abstract: For the successful commercialization of thermoelectric generator (TEG) devices, efficient thermoelectric materials and reliable electrode bonding with high thermal stability are essential. In this study, we synthesized conducting pastes based on Cu nanoparticles and developed a low-temperature and low-pressure sinter-bonding method for TEG devices using these pastes. Cu nanoparticle paste (CNP) bonding layer exhibited high shear strength up to 16.4 MPa, and low thermal contact resistance of 6.4 × 10−7 m2K/W. A 4-chip Bi2Te3-based TEG device bonded using CNP achieved a power density of 0.76 W/cm2 under a large temperature gradient of 330 °C. The CNP bonding joints retained their physical properties at temperatures up to 350 °C, thereby extending the operational temperature range of current Bi2Te3-based TEG devices. This approach overcomes the limitations of conventional Sn-based solders without relying on costly Ag nanoparticles, while achieving improved high-temperature performance of TEG devices. © 2026 The Authors.

Enhancing Thermoelectric Properties of Bi0.4Sb1.6Te3 by Embedding SiO2 Nanoparticles

2026-01-31T15:00:00Z

Title: Enhancing Thermoelectric Properties of Bi0.4Sb1.6Te3 by Embedding SiO2 Nanoparticles Author(s): Park, Jungmin; Ye, Sung Wook; Kim, Jong Ryeol; Lee, Dong Hyun; Seo, Sehoon; Yoo, Hyesun; Kim, Jeongmin; Hyun, Dong Choon; Roh, Jong Wook Abstract: Thermoelectric performance in Bi2Te3-materials can be significantly improved by embedding SiO2 nanoparticles. In this study, SiO2 nanoparticles (similar to 80 nm) are synthesized and incorporated into p-type Bi0.4Sb1.6Te3 in small amounts (0.01 to 0.06 vol %) using spark plasma sintering. The embedded SiO2 nanoparticles are confirmed to be well-dispersed within the Bi0.4Sb1.6Te3 matrix, which effectively enhances the thermoelectric performance by increasing the power factor and reducing thermal conductivity. Notably, the optimal enhancement was observed at 0.01 vol % SiO2 nanoparticles. At this sample, the carrier filtering effect was effective, and lattice thermal conductivity decreased by 43% compared to pristine Bi0.4Sb1.6Te3. Consequently, the figure of merit (zT) reached 1.15, a 47% improvement over the pristine sample at room temperature, with a maximum zT of 1.28 at 363 K. These findings highlight that achieving a well-dispersed distribution of SiO2 nanoparticles in Bi0.4Sb1.6Te3 is essential for optimizing both electrical and thermal transport properties, thereby significantly enhancing the overall thermoelectric performance.

Synergistic energy storage in Ni/Mn carbonate-hydroxide bilayer electrodes for asymmetric supercapacitors

2026-03-31T15:00:00Z

Title: Synergistic energy storage in Ni/Mn carbonate-hydroxide bilayer electrodes for asymmetric supercapacitors Author(s): Lee, Damin; Kim, Dong Hwan; Chung, Seok-Hwan; Roh, Jong Wook; Kim, Jeongmin Abstract: The electrochemical performance of the supercapacitor electrodes was enhanced by integrating a 3D Ni foam substrate with transition metal carbonate–hydroxide composites possessing improved surface wettability. In this study, two types of active materials were synthesized individually, with Ni2(CO3)(OH)2 forming nanowires and NiMn(CO3)(OH)2 forming nanoplates. These materials were used to fabricate both single-layer electrodes and bilayer electrode architectures. In the single-layer configuration, the Ni2(CO3)(OH)2 electrode delivered a specific capacity of 128.3 mAh g−1, while the NiMn(CO3)(OH)2 electrode exhibited 74.5 mAh g−1 at a current density of 3 A g−1. In contrast, the bilayer structures showed substantially improved performance. The Ni2(CO3)(OH)2–NiMn(CO3)(OH)2 electrode achieved 201.4 mAh g−1, and the NiMn(CO3)(OH)2–Ni2(CO3)(OH)2 electrode reached 172.2 mAh g−1 The enhanced performance resulted from the increased effective surface area and the complementary electrochemical reactions facilitated by the bilayer configuration. The cycling stabilities of the two bilayer electrodes, Ni2(CO3)(OH)2–NiMn(CO3)(OH)2 and NiMn(CO3)(OH)2–Ni2(CO3)(OH)2, were determined to be 89.6 % and 84.3 %, respectively. In addition, an asymmetric supercapacitor with a Ni2(CO3)(OH)2–NiMn(CO3)(OH)2 positive electrode and a graphene negative electrode exhibited an energy density of 39.6 Wh kg−1 and a power density of 580.7 W kg−1 at a current density of 2 A g−1. These results highlight the potential of supercapacitors based on a bilayer electrode structure. © 2026 Elsevier B.V.