Journal of Powder Materials

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Volume 31(6); December 2024

Critical Reviews

Epsilon Iron Oxide (ε-Fe₂O₃) as an Electromagnetic Functional Material: Properties, Synthesis, and Applications: Ji Hyeong Jeong, Hwan Hee Kim, Jung-Goo Lee, Youn-Kyoung Baek; J Powder Mater. 2024;31(6):465-479. Published online December 31, 2024; DOI: https://doi.org/10.4150/jpm.2024.00290

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Abstract PDF: Iron oxide (ε-Fe₂O₃) is emerging as a promising electromagnetic material due to its unique magnetic and electronic properties. This review focuses on the intrinsic properties of ε-Fe₂O₃, particularly its high coercivity, comparable to that of rare-earth magnets, which is attributed to its significant magnetic anisotropy. These properties render it highly suitable for applications in millimeter wave absorption and high-density magnetic storage media. Furthermore, its semiconducting behavior offers potential applications in photocatalytic hydrogen production. The review also explores various synthesis methods for fabricating ε-Fe₂O₃ as nanoparticles or thin films, emphasizing the optimization of purity and stability. By exploring and harnessing the properties of ε-Fe₂O₃, this study aims to contribute to the advancement of next-generation electromagnetic materials with potential applications in 6G wireless telecommunications, spintronics, high-density data storage, and energy technologies.

Advances in Powder Metallurgy for High-Entropy Alloys: Sheetal Kumar Dewangan, Cheenepalli Nagarjuna, Hansung Lee, K. Raja Rao, Man Mohan, Reliance Jain, Byungmin Ahn; J Powder Mater. 2024;31(6):480-492. Published online December 31, 2024; DOI: https://doi.org/10.4150/jpm.2024.00297

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Abstract PDF: High-entropy alloys (HEAs) represent a revolutionary class of materials characterized by their multi-principal element compositions and exceptional mechanical properties. Powder metallurgy, a versatile and cost-effective manufacturing process, offers significant advantages for the development of HEAs, including precise control over their composition, microstructure, and mechanical properties. This review explores innovative approaches integrating powder metallurgy techniques in the synthesis and optimization of HEAs. Key advances in powder production, sintering methods, and additive manufacturing are examined, highlighting their roles in improving the performance, advancement, and applicability of HEAs. The review also discusses the mechanical properties, potential industrial applications, and future trends in the field, providing a comprehensive overview of the current state and future prospects of HEA development using powder metallurgy.

Research Articles

Effect of Calcium Addition on the High-Temperature Recovery of Nd and Dy from Nd-Fe-B Scrap Using Mg-Based Extractants: Hyoseop Kim; J Powder Mater. 2024;31(6):493-499. Published online December 31, 2024; DOI: https://doi.org/10.4150/jpm.2024.00283

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Abstract PDF: This study investigated whether calcium (Ca) addition improved the recovery of neodymium (Nd) and dysprosium (Dy) from Nd-Fe-B magnet scrap using magnesium (Mg)-based liquid metal extraction (LME). Traditional LME processes are limited to temperatures up to 850 °C due to oxidation issues, reducing the efficiency of rare earth element (REE) recovery, especially for Dy. By adding 10 wt.% Ca to Mg and increasing the processing temperature to 1,000 °C, we achieved nearly 100% Nd and approximately 38% Dy recovery, compared to 91% and 28%, respectively, with pure Mg at 850 °C. However, excessive Ca addition (20 wt.%) decreased the recovery efficiency due to the formation of stable intermetallic compounds. These results highlight the critical role of Ca in optimizing REE recycling from Nd-Fe-B magnet scrap.

Design of Conductive Inks Containing Carbon Black and Silver Nanowires for Patternable Screen-Printing on Fabrics: Seokhwan Kim, Geumseong Lee, Jinwoo Park, Dahye Shin, Ki-Il Park, Kyoung Jin Jung, Yuho Min; J Powder Mater. 2024;31(6):500-507. Published online December 31, 2024; DOI: https://doi.org/10.4150/jpm.2024.00409

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Abstract PDF: This study developed conductive inks composed of carbon black (CB) and silver nanowires (Ag NWs) for cost-effective screen-printing on fabrics. The Ag NW density within the CB matrix was precisely controlled, achieving tunable electrical conductivity with minimal Ag NW usage. The resulting inks were successfully patterned into shapes such as square grids and circles on textile surfaces, demonstrating excellent conductivity and fidelity. Adding 19.9 wt% Ag NWs reduced sheet resistance by ~92% compared to CB-only inks, highlighting the effectiveness and potential of this hybrid approach for cost-effective, high-performance textile-based electronics. The one-dimensional morphology of Ag NWs facilitated the formation of conductive percolation networks, creating efficient electron pathways within the CB matrix even at low loadings. This work advances the field of CB-based conductive inks and provides a scalable and practical method for producing functional, patterned electronic textiles.

Development of Highly Transparent and Thermo-Shielding Flexible Film via Colloidal ITO Nanocrystals: Hyoin Bae, Hyeyeon Jung, Juna Lee, Dahye Shin, Sungyeon Heo; J Powder Mater. 2024;31(6):508-512. Published online December 31, 2024; DOI: https://doi.org/10.4150/jpm.2024.00423

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Abstract PDF: Infrared radiation accounts for approximately 50% of the solar spectrum. Specifically, the near-infrared (NIR) spectrum, ranging from 760 nm to 2500 nm, is primarily responsible for solar heat gain, increasing indoor temperatures and reducing heating and cooling efficiency. To address this issue, we developed a highly transparent thermo-shielding flexible film that maintains a high transmittance of the visible region (T = 80%) while reducing the transmittance of the NIR region (T ≈ 0%). NIR-absorbing indium tin oxide (ITO) nanocrystals were coated onto polyethylene terephthalate (PET) films, and both films were sandwiched to improve the NIR absorption properties and protect the nanocrystal film layer. The fabricated films were applied to a model house and decreased the indoor temperature by approximately 8°C. Our study demonstrates that energy consumption can be reduced by ITO nanocrystal-coated flexible films, with potential implications for the smart window and mobility markets.

Fabrication of Al₁₈B₄O₃₃ Spherical Powder with Increased Fluidity via Control of B₂O₃ Particle Size and Distribution: Kiho Song, Sang in Lee, Hyunseung Song, Changui Ahn; J Powder Mater. 2024;31(6):513-520. Published online December 31, 2024; DOI: https://doi.org/10.4150/jpm.2024.00304

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Abstract PDF: Ceramic materials have become essential due to their high durability, chemical stability, and excellent thermal stability in various advanced industries such as aerospace, automotive, and semiconductor. However, high-performance ceramic materials face limitations in commercialization due to the high cost of raw materials and complex manufacturing processes. Aluminum borate (Al₁₈B₄O₃₃) has emerged as a promising alternative due to its superior mechanical strength and thermal stability, despite its simple manufacturing process and low production cost. In this study, we propose a method for producing Al₁₈B₄O₃₃ spherical powder with increased uniformity and high flowability by controlling the particle size of B₂O₃. The content ratio of the manufactured Al18B4O33 spherical powder was Al2O3: B2O3 = 87:13, and it exhibited a 17% reduction in the Hausner ratio (1.04) and a 29% decrease in the angle of repose (23.9°) compared to pre-milling conditions, demonstrating excellent flowability.

Fabrication and High-Temperature Performance Evaluation of Light-Weight Insulation Materials and Coatings for Reusable Thermal Protection Systems: Min-Soo Nam, Jong-Il Kim, Jaesung Shin, Hyeonjun Kim, Bum-Seok Oh, Seongwon Kim; J Powder Mater. 2024;31(6):521-529. Published online December 31, 2024; DOI: https://doi.org/10.4150/jpm.2024.00318

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Abstract PDF: Light-weight ceramic insulation materials and high-emissivity coatings were fabricated for reusable thermal protection systems (TPS). Alumina-silica fibers and boric acid were used to fabricate the insulation, which was heat treated at 1250 °C. High-emissivity coating of borosilicate glass modified with TaSi2, MoSi2, and SiB6 was applied via dip-and-spray coating methods and heat-treated at 1100°C. Testing in a high-velocity oxygen fuel environment at temperatures over 1100 °C for 120 seconds showed that the rigid structures withstood the flame robustly. The coating effectively infiltrated into the fibers, confirmed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction analyses. Although some oxidation of TaSi2 occurred, thereby increasing the Ta2O5 and SiO2 phases, no significant phase changes or performance degradation were observed. These results demonstrate the potential of these materials for reusable TPS applications in extreme thermal environments.

Fabrication of SiC_f/SiC Composites with a BN Interphase Prepared by the Wet Method: Kyung Ho Kim, Yoonsoo Han; J Powder Mater. 2024;31(6):530-536. Published online December 31, 2024; DOI: https://doi.org/10.4150/jpm.2024.00339

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Abstract PDF: This study presents a cost-effective wet chemical coating process for fabricating a boron nitride (BN) interphase on silicon carbide (SiC) fibers, increasing the oxidation resistance and performance of SiCf/SiC ceramic matrix composites. Using urea as a precursor, optimal nitriding conditions were determined by adjusting the composition, concentration, and immersion time. X-ray diffraction analysis revealed distinct BN phase formation at 1300°C and 1500°C, while a mixture of BN and B₂O₃ was observed at 1200°C. HF treatment improved coating uniformity by removing SiO₂ layers formed during the de-sizing process. Optimization of the boric acid-to-urea molar ratio resulted in a uniform, 130-nm-thick BN layer. This study demonstrates that the wet coating process offers a viable and economical alternative to chemical vapor deposition for fabricating high-performance BN interphases in SiCf/SiC composites that are suitable for high-temperature applications.

Hot-Cracking Behaviors in (CoNi)₈₅Mo₁₅ Medium-Entropy Alloys Manufactured via Powder Bed Fusion: Seungjin Nam, Heechan Jung, Haeum Park, Chahee Jung, Jeong Min Park, Hyoung Seop Kim, Seok Su Sohn; J Powder Mater. 2024;31(6):537-545. Published online December 31, 2024; DOI: https://doi.org/10.4150/jpm.2024.00262

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Abstract PDF: Additive manufacturing makes it possible to improve the mechanical properties of alloys through segregation engineering of specific alloying elements into the dislocation cell structure. In this study, we investigated the mechanical and microstructural characteristics of CoNi-based medium-entropy alloys (MEAs), including the refractory alloying element Mo with a large atomic radius, manufactured via laser-powder bed fusion (L-PBF). In an analysis of the printability depending on the processing parameters, we achieved a high compressive yield strength up to 653 MPa in L-PBF for (CoNi)85Mo15 MEAs. However, severe residual stress remained at high-angle grain boundaries, and a brittle µ phase was precipitated at Mo-segregated dislocation cells. These resulted in hot-cracking behaviors in (CoNi)85Mo15 MEAs during L-PBF. These findings highlight the need for further research to adjust the Mo content and processing techniques to mitigate cracking behaviors in L-PBF-manufactured (CoNi)85Mo15 MEAs.

High-Temperature Steam Oxidation Behavior of Silicide- or Aluminide- Coated Mo and Nb Refractory Metals: Woojin Lim, Je-Kyun Baek, JaeJoon Kim, Hyun Gil Kim, Ho Jin Ryu; J Powder Mater. 2024;31(6):546-555. Published online December 31, 2024; DOI: https://doi.org/10.4150/jpm.2024.00381

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Abstract PDF: Refractory materials, such as molybdenum and niobium, are potential candidates for cladding material due to their high melting temperatures and desirable mechanical properties at higher temperatures than those of zirconium alloys. However, refractory materials have low resistance to oxidation at elevated temperatures. Therefore, this study examined silicide or aluminide surface coatings as protection against rapid oxidation of refractory materials at elevated temperatures for a potential accident-tolerant fuel cladding. Silicide or aluminide layers were formed on refractory metal substrates by using the pack cementation method. The steam oxidation behavior of both coated and uncoated samples was compared by thermogravimetric analysis at 1200°C. The weight changes of the coated samples were greatly reduced than those of uncoated samples. Microstructural analyses demonstrated that the silicide and aluminide layers were oxidized to form a protective surface oxide that prevented rapid oxidation of the refractory substrate at elevated temperatures.

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