Journal of Powder Materials

[Korean]
Flexible Hybrid Energy Harvester based on Thermoelectric Composite Film and Electrospun Piezopolymer Membranes: Hyomin Jeon, Cheol Min Kim, Hyeon Jun Park, Bitna Bae, Hyejeong Choi, HakSu Jang, Kwi-Il Park; Received November 29, 2024 Accepted December 30, 2024 Published online March 4, 2025; DOI: https://doi.org/10.4150/jpm.2024.00458 [Epub ahead of print]

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Abstract PDF: A hybrid energy harvester that consisted of thermoelectric (TE) composite film and electrospun piezoelectric (PE) polymeric membranes was constructed. TE composites were fabricated by dispersing inorganic TE powders inside polyvinylidene fluoride elastomer using a drop-casting technique. The polyvinylidene fluoride-trifluoroethylene, which was chosen due to its excellent chemical resistance, mechanical stability, and biocompatibility, was electrospun onto an aluminum foil to fabricate the ultra-flexible PE membranes. To create a hybrid energy harvester that can simultaneously convert heat and mechanical energy resources into electricity, the TE composite films attached to the PE membrane were encapsulated with protective polydimethylsiloxane. The fabricated energy harvester converted the outputs with a maximum voltage of 4 V (PE performance) and current signals of 0.2 μA (TE performance) under periodical heat input and mechanical bending in hybrid modes. This study demonstrates the potential of the hybrid energy harvester for powering flexible and wearable electronics, offering a sustainable and reliable power source.

[Korean]
Friction Stir Spot Welding Characteristics of Dissimilar Materials of Aluminum-Based Damping Composites and Steel Plates: Si-Seon Park, Young-Keun Jeong; J Powder Mater. 2025;32(1):43-49. Published online February 28, 2025; DOI: https://doi.org/10.4150/jpm.2025.00010

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Abstract PDF: Friction Stir Spot Welding (FSSW) is a solid-state welding technology that is rapidly growing in the automotive industry. Achieving superior welding characteristics requires the proper selection of tool geometry and process conditions. In this study, FSSW was performed on dissimilar materials comprising AA5052-HO/hot-melt aluminum alloy sheets and Steel Plate Cold Rolled for Deep Drawing Use(SPCUD) steel sheets. The effects of tool geometry, plate arrangement, and tool plunge depth on the welding process were investigated. At the joint interface between the aluminum alloy and the steel sheet, new intermetallic compounds (IMCs) were observed. As the plunge depth increased, thicker and more continuous IMC layers were formed. However, excessive plunge depth led to discontinuous layers and cracking defects. An analysis of the IMCs revealed a correlation between the IMC thickness and the shear tensile load. Furthermore, compared to the conventional Al-Top arrangement, the St-Top arrangement exhibited reduced deformation and superior shear tensile load values. These findings indicate that plate arrangement significantly influences the mechanical properties of the joint.

[Korean]
Effect of Hatch Spacing on the Microstructure and Mechanical Properties of SA508 Gr.3 Steel Fabricated by Laser Powder Bed Fusion: Yuanjiu Huang, Ho Jin Ryu, Kee-Ahn Lee; J Powder Mater. 2025;32(1):50-58. Published online February 28, 2025; DOI: https://doi.org/10.4150/jpm.2024.00479

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Abstract PDF: This study investigated the effect of the hatch spacing parameter on the microstructure and mechanical properties of SA508 Gr.3 steel manufactured by laser powder bed fusion (L-PBF) for a nuclear pressure vessel. Materials were prepared with varying hatch spacing (0.04 mm [H4] and 0.06 mm [H6]). The H4 exhibited finer and more uniformly distributed grains, while the H6 showed less porosity and a lower defect fraction. The yield strength of the H4 material was higher than that of the H6 material, but there was a smaller difference between the materials in tensile strength. The measured elongation was 5.65% for the H4 material and 10.41% for the H6 material, showing a significantly higher value for H6. An explanation for this is that although the H4 material had a microstructure of small and uniform grains, it contained larger and more numerous pore defects than the H6 material, facilitating stress concentration and the initiation of microcracks.

[English]
Comparative Study of Reduced Graphene Oxide Aerogels and Films for Supercapacitor Electrodes: Sunghee Choi, Seulgi Kim, Seojin Woo, Dongju Lee; J Powder Mater. 2025;32(1):23-29. Published online February 28, 2025; DOI: https://doi.org/10.4150/jpm.2024.00472

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Abstract PDF: Supercapacitors, renowned for their high power density and rapid charge-discharge rates, are limited by their low energy density. This limitation has prompted the need for advanced electrode materials. The present study investigated reduced graphene oxide (rGO) in two distinct structures, as a film and as an aerogel, for use as supercapacitor electrodes. The rGO film, prepared by vacuum filtration and thermal reduction, exhibited a compact, lamellar structure, while the aerogel, synthesized through hydrothermal treatment, was a highly porous three-dimensional network. Electrochemical analyses demonstrated the aerogel’s superior performance, as shown by a specific capacitance of 121.2 F/g at 5 mV/s, with 94% capacitance retention after 10,000 cycles. These findings emphasize the importance of structural design in optimizing ion accessibility and charge transfer. They also demonstrate the potential of rGO aerogels for increasing the energy storage efficiency of advanced supercapacitor systems.

[Korean]
3D-Printed Stretchable Electrodes Enabled by a Titanium/Acrylamide-Based Hydrogel Nanocomposite: Se Jin Choi, Han Eol Lee; J Powder Mater. 2025;32(1):67-72. Published online February 28, 2025; DOI: https://doi.org/10.4150/jpm.2024.00465

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Abstract PDF: Wearable electronics have been the focus of considerable interest in various fields, such as human-machine interfaces, soft robotics, and medical treatments, due to their flexibility, stretchability, and light weight. To address the shortcomings of existing metal thin film-based wearable devices, stretchable conductive polymers have been developed. In particular, double networking hydrogels are being actively studied as a polymer with a three-dimensional stereoscopic structure that can be patterned. Nonetheless, they have shortcomings such as poor electrical properties and cumbersome manufacturing processes, making it difficult to apply them in electronic devices. Herein, we report 3D-printed stretchable electrodes enabled by a titanium/polyacrylamide-alginate-based hydrogel nanocomposite. This research suggests the strategy for resolving the challenges of high costs and complex fabrication processes associated with stretchable electrode, providing a solution to accelerate the commercialization of wearable electronic devices.

[Korean]
Optimized Process and Mechanical and Electrical Analysis of Polyimide/Pb(Zr,Ti)O₃-Based Flexible Piezoelectric Composites: Junki Lee, Sang-il Yoon, Hyunseung Kim, Chang Kyu Jeong; J Powder Mater. 2025;32(1):16-22. Published online February 28, 2025; DOI: https://doi.org/10.4150/jpm.2024.00444

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Abstract PDF: Piezoelectric composites have attracted significant research interest as sustainable power sources for electronic devices due to their high mechanical stability and electrical output characteristics. This study investigated the optimal processing conditions for fabricating a flexible piezoelectric energy harvester based on Pb(Zr,Ti)O₃ (PZT) powder and a polyimide (PI) matrix composite. Various parameters, including the optimal mixing ratio of PI/PZT, ultrasonic treatment, homogenization, vacuum oven, and UV/O₃ treatment, were optimized to achieve a uniform piezoelectric composite. A PZT content of 30 wt% and 20 minutes of homogenization were identified as the most effective conditions for increasing the uniformity of the composite. The optimized composite exhibited a high piezoelectric coefficient, a typical P-E hysteresis loop, and dielectric properties, exhibiting a voltage output that adjusts in response to variations in the applied touch force. This study provides foundational data for the uniform fabrication of flexible piezoelectric energy harvesters and next-generation miniaturized electronic devices.

[English]
The Effect of a CNT/MnO₂ Nanoparticle Composite–Based Multi-Shell Typed Electrode for a Fiber Supercapacitor (FSC): Yeonggwon Kim, Hyung Woo Lee; J Powder Mater. 2025;32(1):30-36. Published online February 28, 2025; DOI: https://doi.org/10.4150/jpm.2024.00416

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Abstract PDF: Fiber supercapacitors have attracted significant interest as potential textile energy storage devices due to their remarkable flexibility and rapid charge/discharge capabilities. This study describes the fabrication of a composite fiber supercapacitor (FSC) electrode through a multi-shell architecture, featuring layers of carbon nanotube (CNT) conductive shells and MnO₂ nanoparticle active shells. The number of layers was adjusted to assess their impact on FSC energy storage performance. Increasing the number of shells reduced electrode resistance and enhanced pseudocapacitive characteristics. Compared to the MnS@1 electrode, the MnS@5 electrode exhibited a high areal capacitance of 301.2 mF/cm², a 411% increase, but showed a higher charge transfer resistance (RCT) of 701.6 Ω. This is attributed to reduced ion diffusion and charge transfer ability resulting from the thicker multi-shell configuration. These results indicate that fine-tuning the quantity of shells is crucial for achieving an optimal balance between energy storage efficiency and stability.

[English]
Recent Advances in Thermoelectric Materials and Devices: Improving Power Generation Performance: Momanyi Amos Okirigiti, Cheol Min Kim, Hyejeong Choi, Nagamalleswara Rao Alluri, Kwi-Il Park; J Powder Mater. 2025;32(1):1-15. Published online February 28, 2025; DOI: https://doi.org/10.4150/jpm.2024.00395

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Abstract PDF: Thermoelectric materials have been the focus of extensive research interest in recent years due to their potential in clean power generation from waste heat. Their conversion efficiency is primarily reflected by the dimensionless figure of merit, with higher values indicating better performance. There is a pressing need to discover materials that increase output power and improve performance, from the material level to device fabrication. This review provides a comprehensive analysis of recent advancements, such as Bi2Te3-based nanostructures that reduce thermal conductivity while maintaining electrical conductivity, GeTe-based high entropy alloys that utilize multiple elements for improved thermoelectric properties, porous metal-organic frameworks offering tunable structures, and organic/hybrid films that present low-cost, flexible solutions. Innovations in thermoelectric generator designs, such as asymmetrical geometries, segmented modules, and flexible devices, have further contributed to increased efficiency and output power. Together, these developments are paving the way for more effective thermoelectric technologies in sustainable energy generation.

[Korean]
Fabrication and Optimization of Al₂O₃ Microchannels Using DLP-Based 3D Printing: Jun-Min Cho, Yong-Jun Seo, Yoon-Soo Han; J Powder Mater. 2025;32(1):59-66. Published online February 28, 2025; DOI: https://doi.org/10.4150/jpm.2024.00346

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Abstract PDF: This study focused on optimizing the digital light processing (DLP) 3D printing process for high-precision ceramic components using alumina-based slurries. Key challenges, such as cracking during debinding and precision loss due to slurry sedimentation, were addressed by evaluating the exposure time and the nano-to-micro alumina powder ratios. The optimal conditions—exposure time of 15 seconds and a 1:9 mixing ratio—minimized cracking, improved gas flow during debinding, and increased structural precision. Microchannels with diameters above 1.2 mm were successfully fabricated, but channels below 0.8 mm faced challenges due to slurry accumulation and over-curing. These results establish a reliable process for fabricating complex ceramic components with improved precision and structural stability. The findings have significant potential for applications in high-value industries, including aerospace, energy, and healthcare, by providing a foundation for the efficient and accurate production of advanced ceramic structures.

[English]
Effect of the Cross-rolling Process on the Microstructures and Mechanical Properties of 9Cr-1W ODS Steel: Bu-An Kim, Sanghoon Noh; J Powder Mater. 2025;32(1):37-42. Published online February 28, 2025; DOI: https://doi.org/10.4150/jpm.2024.00332

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Abstract PDF: This study employed a cross-rolling process to fabricate oxide dispersion strengthened (ODS) steel plates and investigated their microstructures and mechanical properties. The 9Cr-1W ODS ferritic steel was fabricated using mechanical alloying and hot isostatic pressing. The hot cross-rolling process produced thick ODS ferritic steel plates with a well-extended rectangular shape. The working direction greatly affected the grain structure and crystal texture of the ODS ferritic steel. Cross-rolled plates showed fine micro-grains with random crystal orientation, while unidirectionally rolled plates exhibited a strong orientation with larger, elongated grains. Transmission electron microscopy revealed a uniform distribution of nano-oxide particles in both rolling methods, with no major differences. Tensile tests of the ODS ferritic steel plates showed that the unidirectional rolled plates had anisotropic elongation, while cross-rolled plates exhibited isotropic behavior with uniform elongation. Cross-rolling produced finer, more uniform grains, reducing anisotropy and improving mechanical properties, making it ideal for manufacturing wide ODS steel components.

[Korean]
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.

[English]
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.

[English]
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.

[Korean]
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.

[Korean]
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.

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