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• Understanding the unique appearance behavior of shear bands during tensile deformation of α-brass at 4.2 K
  Seon-Keun Oh, Sang-Hun Shim, Young-Kyun Kim, Young-Sang Na
  Materials Science and Engineering: A.2025; 945: 148989.     CrossRef

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• Review of “Integrated Computer-Aided Process Engineering Session in the 17th International Symposium on Novel and Nano Materials (ISNNM, 14–18 November 2022)”
  Yeon-Joo Lee, Pil-Ryung Cha, Hyoung-Seop Kim, Hyun-Joo Choi
  MATERIALS TRANSACTIONS.2025; 66(1): 144.     CrossRef

The emergence of ferrous-medium entropy alloys (FeMEAs) with excellent tensile properties represents a potential direction for designing alloys based on metastable engineering. In this study, an FeMEA is successfully fabricated using laser powder bed fusion (LPBF), a metal additive manufacturing technology. Tensile tests are conducted on the LPBF-processed FeMEA at room temperature and cryogenic temperatures (77 K). At 77 K, the LPBF-processed FeMEA exhibits high yield strength and excellent ultimate tensile strength through active deformation-induced martensitic transformation. Furthermore, due to the low stability of the face-centered cubic (FCC) phase of the LPBF-processed FeMEA based on nano-scale solute heterogeneity, stress-induced martensitic transformation occurs, accompanied by the appearance of a yield point phenomenon during cryogenic tensile deformation. This study elucidates the origin of the yield point phenomenon and deformation behavior of the FeMEA at 77 K.

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• Effect of Building Orientation on Tensile Properties of Hastelloy X alloy Manufactured by Laser Powder Bed Fusion
  Seong-June Youn, GooWon Noh, Seok Su Sohn, Young-Sang Na, Young-Kyun Kim
  Journal of Powder Materials.2025; 32(2): 130.     CrossRef
• Thermodynamic and Electronic Descriptor-Driven Machine Learning for Phase Prediction in High-Entropy Alloys: Experimental Validation
  Nguyen Lam Khoa, Nguyen Duy Khanh, Hoang Thi Ngoc Quyen, Nguyen Thi Hoang, Oanh, Le Hong Thang, Nguyen Hoa Khiem, Nguyen Hoang Viet
  Journal of Powder Materials.2025; 32(3): 191.     CrossRef
• Cryogenic tensile behavior of carbon-doped CoCrFeMnNi high-entropy alloys additively manufactured by laser powder bed fusion
  Haeum Park, Hyeonseok Kwon, Kyung Tae Kim, Ji-Hun Yu, Jungho Choe, Hyokyung Sung, Hyoung Seop Kim, Jung Gi Kim, Jeong Min Park
  Additive Manufacturing.2024; 86: 104223.     CrossRef
• Recent progress in high-entropy alloys for laser powder bed fusion: Design, processing, microstructure, and performance
  Asker Jarlöv, Zhiguang Zhu, Weiming Ji, Shubo Gao, Zhiheng Hu, Priyanka Vivegananthan, Yujia Tian, Devesh Raju Kripalani, Haiyang Fan, Hang Li Seet, Changjun Han, Liming Tan, Feng Liu, Mui Ling Sharon Nai, Kun Zhou
  Materials Science and Engineering: R: Reports.2024; 161: 100834.     CrossRef

This study aimed to develop a solid self-nanoemulsifying drug delivery system (solid-SNEDDS) to enhance the formulation of ketoconazole (KTZ), a BCS Class II drug with poor solubility. Ketoconazole, which is insoluble above pH 3, requires solubilization for effective delivery. This SNEDDS comprises oil, surfactant, and co-surfactant, which spontaneously emulsify in the gastrointestinal tract environment to form nanoemulsions with droplet sizes less than 100 nm. The optimal SNE-vehicle composition of oleic acid, TPGS, and PEG 400 at a 10:80:10 weight ratio was determined based on the smallest droplet size achieved. This composition was used to prepare liquid SNEDDS containing ketoconazole. The droplet size and polydispersity index (PDI) of the resulting liquid SNEDDS were analyzed. Subsequently, solid-SNEDDS was fabricated using a spray-drying method with solidifying carriers such as silicon dioxide, crospovidone, and magnesium alumetasilicate. The physicochemical properties of the solid-SNEDDS were characterized by scanning electron microscopy and powder X-ray diffraction, and its solubility, droplet size, and PDI were evaluated. In particular, the solid-SNEDDS containing ketoconazole and crospovidone in a 2:1 weight ratio exhibited significantly enhanced solubility, highlighting its potential for improved medication adherence and dissolution rates.

This study aims to prepare a colloidal silica-containing powder to enhance the solubility and dissolution rate of rivaroxaban using a self-nanoemulsifying drug delivery system (SNEDDS). We investigate the impact of colloidal silica on a nanoemulsion system for preparing powdered SNEDDS. The liquid SNEDDS comprises 30/20/50 (w/w/w) Peceol/ Cremophor RH40/Tween 80, which results in the formation of the smallest droplets. Three powdered SNEDDS formulations are prepared by suspending the liquid SNEDDS formulation using colloidal silica and spray drying. The powdered SNEDDS prepared with liquid SNEDDS and colloidal silica at a ratio of 1/0.5 (w/w) exhibits the highest water solubility (0.94 ± 0.62 vs. 26.70 ± 1.81 μg/mL) and dissolution rate (38.4 ± 3.6 vs. 85.5 ± 3.4%, 45 min) when compared to the drug alone. Morphologically, the liquid SNEDDS is adsorbed onto colloidal silica and forms smaller particles. In conclusion, an SNEDDS containing rivaroxaban, prepared using colloidal silica, facilitates the creation of a nanoemulsion and enhances the water solubility of rivaroxaban. Accordingly, this technology holds significant potential for commercialization.

In this study, we evaluated the effects of acid leaching on the properties of Cr powder synthesized using self-propagating high-temperature synthesis (SHS). Cr powder was synthesized from a mixture of Cr2O3 and magnesium (Mg) powders using the SHS Process, and the byproducts after the reaction were removed using acid leaching. The properties of the recovered Cr powder were analyzed via X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), particle size analysis (PSA), and oxygen content analysis. The results show that perfect selective leaching of Cr is challenging because of various factors such as incomplete reaction, reaction kinetics, the presence of impurities, and incompatibility between the acid and metal mixture. Therefore, this study provides essential information on the properties under acidic conditions during the production of high-quality Cr powder using a self-propagating high-temperature synthesis method.

The objective of this study is to assess the impact of spray drying conditions on medium-chain triglyceride (MCT) loading, solubility, and release of an MCT-loaded solid self-emulsifying system in a water-insoluble oily substance. MCT-loaded solid self-emulsifying systems are prepared by spray drying with SDS and calcium silicate. The effects of inlet temperature (60, 80, or 100°C) and feed solution composition (0, 10, 50, 90, or 100% ethanol) on physicochemical properties of MCT-loaded solid self-emulsifying systems are studied. The inlet temperature significantly affects the water solubility of MCT. Moreover, the feed solution composition significantly affects water solubility, release rate, and MCT loading. The MCT-loaded solid self-emulsifying system obtained at 60°C using 90% ethanol feed solution shows the best physicochemical properties among the synthesized products and exhibits better water solubility (4.43 ± 0.44 vs. 0 μg/mL) and release (94.4 ± 1.6 vs. 32.8 ± 7.4%, 60 min) than a commercial product. Furthermore, the MCT-loaded solid self-emulsifying system shows an excellent emulsion droplet size (approximately 230 nm).

Thermal protection systems (TPS) are a group of materials that are indispensable for protecting spacecraft from the aerodynamic heating occurring during entry into an atmosphere. Among candidate materials for TPS, ceramic insulation materials are usually considered for reusable TPS. In this study, ceramic insulation materials, such as alumina enhanced thermal barrier (AETB), are fabricated via typical ceramic processing from ceramic fiber and additives. Mixtures of silica and alumina fibers are used as raw materials, with the addition of B4C to bind fibers together. Reaction-cured glass is also added on top of AETB to induce water-proof functionality or high emissivity. Some issues, such as the elimination of clumps in the AETB, and processing difficulties in the production of reusable surface insulation are reported as well.

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• 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
  Journal of Powder Materials.2024; 31(6): 521.     CrossRef

The low-temperature sinterability of TiO₂-CuO systems was investigated using a solid solution of SnO₂. Sample powders were prepared through conventional ball milling of mixed raw powders. With the SnO₂ content, the compositions of the samples were Ti_1-xSn_xO₂-CuO(2 wt.%) in the range of x ≤ 0.08. Compared with the samples without SnO₂ addition, the densification was enhanced when the samples were sintered at 900°C. The dominant mass transport mechanism seemed to be grain-boundary diffusion during heat treatment at 900°C, where active grain-boundary diffusion was responsible for the improved densification. The rapid grain growth featured by activated sintering was also obstructed with the addition of SnO₂. This suggested that both CuO as an activator and SnO₂ dopant synergistically reduced the sintering temperature of TiO₂.

Tungsten carbide is widely used in carbide tools. However, its production process generates a significant number of end-of-life products and by-products. Therefore, it is necessary to develop efficient recycling methods and investigate the remanufacturing of tungsten carbide using recycled materials. Herein, we have recovered 99.9% of the tungsten in cemented carbide hard scrap as tungsten oxide via an alkali leaching process. Subsequently, using the recovered tungsten oxide as a starting material, tungsten carbide has been produced by employing a self-propagating high-temperature synthesis (SHS) method. SHS is advantageous as it reduces the reaction time and is energy-efficient. Tungsten carbide with a carbon content of 6.18 wt % and a particle size of 116 nm has been successfully synthesized by optimizing the SHS process parameters, pulverization, and mixing. In this study, a series of processes for the highefficiency recycling and quality improvement of tungsten-based materials have been developed.

Oxide dispersion-strengthened (ODS) steel has excellent high-temperature properties, corrosion resistance, and oxidation resistance, and is expected to be applicable in various fields. Recently, various studies on mechanical alloying (MA) have been conducted for the dispersion of oxide particles in ODS steel with a high number density. In this study, ODS steel is manufactured by introducing a complex milling process in which planetary ball milling, cryogenic ball milling, and drum ball milling are sequentially performed, and the microstructure and high-temperature mechanical properties of the ODS steel are investigated. The microstructure observation revealed that the structure is stretched in the extrusion direction, even after the heat treatment. In addition, transmission electron microscopy (TEM) analysis confirmed the presence of oxide particles in the range of 5 to 10 nm. As a result of the room-temperature and high-temperature compression tests, the yield strengths were measured as 1430, 1388, 418, and 163 MPa at 25, 500, 700, and 900°C, respectively. Based on these results, the correlation between the microstructure and mechanical properties of ODS steel manufactured using the composite milling process is also discussed.

The effects of drying temperature on the microstructure of porous W fabricated by the freeze-casting process of tert-butyl alcohol slurry with WO₃ powder was investigated. Green bodies were hydrogen-reduced at 800°C for 1 h and sintered at 1000°C for 6 h. X-ray diffraction analysis revealed that WO₃ powders were completely converted to W without any reaction phases by hydrogen reduction. The sintered body showed pores aligned in the direction of tertbutyl alcohol growth, and the porosity and pore size decreased as the amount of WO₃ increased from 5 to 10v ol%. As the drying temperature of the frozen body increased from -25°C to -10°C, the pore size and thickness of the struts increased. The change in microstructural characteristics based on the amount of powder added and the drying temperature was explained by the growth behavior of the freezing agent and the degree of rearrangement of the solid powder during the solidification of the slurry.

In this study, the layered structures of immiscible Fe and Cu metals were employed to investigate the interface evolution through solid-state mixing. The pure Fe and Cu powders were cold-consolidated by high-pressure torsion (HPT) to fabricate a layered Cu-Fe-Cu structure. The microstructural evolutions and flow of immiscible Fe and Cu metals were investigated following different iterations of HPT processing. The results indicate that the HPTprocessed sample following four iterations showed a sharp chemical boundary between the Fe and Cu layers. In addition, the Cu powders exhibited perfect consolidation through HPT processing. However, the Fe layer contained many microcracks. After 20 iterations of HPT, the shear strain generated by HPT produced interface instability, which caused the initial layered structure to disappear.

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• Characterization of Cu-5Fe (wt.%) fabricated by powder consolidation using high-pressure torsion
  Amar Djemli, Hiba Azzeddine, Piotr Bazarnik, Foudil Sahnoune, Yi Huang, Thierry Baudin, François Brisset, Megumi Kawasaki, Terence G. Langdon
  Journal of Materials Science.2025; 60(40): 19267.     CrossRef
• Supreme tensile properties in precipitation-hardened 316L stainless steel fabricated through powder cold-consolidation and annealing
  Do Won Lee, Peyman Asghari-Rad, Yoon-Uk Heo, Sujung Son, Hyojin Park, Ji-Su Lee, Jae-il Jang, Byeong-Joo Lee, Hyoung Seop Kim
  Materials Science and Engineering: A.2024; 893: 146107.     CrossRef

In this study, the high-temperature oxidation properties of austenitic 316L stainless steel manufactured by laser powder bed fusion (LPBF) is investigated and compared with conventional 316L manufactured by hot rolling (HR). The initial microstructure of LPBF-SS316L exhibits a molten pool ~100 μm in size and grains grown along the building direction. Isotropic grains (~35 μm) are detected in the HR-SS316L. In high-temperature oxidation tests performed at 700°C and 900°C, LPBF-SS316L demonstrates slightly superior high-temperature oxidation resistance compared to HR-SS316L. After the initial oxidation at 700°C, shown as an increase in weight, almost no further oxidation is observed for both materials. At 900°C, the oxidation weight displays a parabolic trend and both materials exhibit similar behavior. However, at 1100°C, LPBF-SS316L oxidizes in a parabolic manner, but HR-SS316L shows a breakaway oxidation behavior. The oxide layers of LPBF-SS316L and HR-SS316L are mainly composed of Cr₂O₃, Febased oxides, and spinel phases. In LPBF-SS316L, a uniform Cr depletion region is observed, whereas a Cr depletion region appears at the grain boundary in HR-SS316L. It is evident from the results that the microstructure and the hightemperature oxidation characteristics and behavior are related.

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• Retention factor-based constitutive model of high-strength austenitic A4–80 bolts after fire exposure
  Hui Wang, Bo Yang, Tao Sun, Weilai Yao, Wei Jiang
  Journal of Constructional Steel Research.2025; 235: 109930.     CrossRef
• Study of structural stability at high temperature of pseudo-single tube with double layer as an alternative method for accident-tolerant fuel cladding
  Jong Woo Kim, Hyeong Woo Min, Jaehwan Ko, Yonghee Kim, Young Soo Yoon
  Journal of Nuclear Materials.2022; 566: 153800.     CrossRef

Zinc selenide (ZnSe) nanoparticles were synthesized in aqueous solution using glutathione (GSH) as a ligand. The influence of the ligand content, reaction temperature, and hydroxyl ion concentration (pH) on the fabrication of the ZnSe particles was investigated. The optical properties of the synthesized ZnSe particles were characterized using various analytical techniques. The nanoparticles absorbed UV-vis light in the range of 350-400 nm, which is shorter than the absorption wavelength of bulk ZnSe particles (460 nm). The lowest ligand concentration for achieving good light absorption and emission properties was 0.6 mmol. The reaction temperature had an impact on the emission properties; photoluminescence spectroscopic analysis showed that the photo-discharge characteristics were greatly enhanced at high temperatures. These discharge characteristics were also affected by the hydroxyl ion concentration in solution; at pH 13, sound emission characteristics were observed, even at a low temperature of 25°C. The manufactured nanoparticles showed excellent light absorption and emission properties, suggesting the possibility of fabricating ZnSe QDs in aqueous solutions at low temperatures.

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• Green synthesis and luminescence characteristics of ZnSe-ZnS core-shell quantum dots
  Geum Ji Back, Ha Yeon Song, Min Seo Lee, Jaesik Yoon, Hyun Seon Hong
  Journal of Crystal Growth.2024; 626: 127475.     CrossRef
• Effect of UV Irradiation on Optical Properties of Water-Based Synthetic Zinc Selenide Quantum Dots
  Geum Ji Back, Yu Jin Kang, I Ju Kang, Jeong Hyeon Lim, Hyun Seon Hong
  Korean Journal of Metals and Materials.2022; 60(2): 160.     CrossRef

In the present study, we investigated the austenite stability of a sintered Fe-based nanocrystalline alloy. The volume fraction of austenite was measured based on the X-ray diffraction data of sintered Fe-based nanocrystalline alloys, which were prepared by high-energy ball milling and spark plasma sintering. The sintered alloy samples showed a higher volume fraction of austenite at room temperature as compared to the equilibrium volume fraction of austenite obtained using thermodynamic calculations, which resulted from the nanosized crystalline structure of the sintered alloy. It was proved that the austenite stability of the sintered Fe-based alloy increased with a rise in the amount of austenite stabilizing elements such as Mn, Ni, and C; however, it increased more effectively with a decrease in the actual grain size. Furthermore, we proposed a new equation to predict the martensite starting temperature for sintered Fe-based alloys.

Nano-sized ZnSe particles are successfully synthesized in an aqueous solution at room temperature using sodium borohydride (NaBH₄) and thioglycolic acid (TGA) as the reducing agent and stabilizer, respectively. The effects of the mass ratio of the reducing agent to Se, stabilizer concentration, and stirring time on the synthesis of the ZnSe nanoparticles are evaluated. The light absorption/emission properties of the synthesized nanoparticles are characterized using ultraviolet-visible (UV-vis) spectroscopy, photoluminescence (PL) spectroscopy, and particle size analyzer (PSA) techniques. At least one mass ratio (NaBH₄/Se) of the reducing agent should be added to produce ZnSe nanoparticles finer than 10 nm and to absorb UV–vis light shorter than the ZnSe bulk absorption wavelength of 460 nm. As the ratio of the reducing agent increases, the absorption wavelengths in the UV-vis curves are blue-shifted. Stirring in the atmosphere acts as a deterrent to the reduction reaction and formation of nanoparticles, but if not stirred in the atmosphere, the result is on par with synthesis in a nitrogen atmosphere. The stabilizer, TGA, has an impact on the Zn precursor synthesis. The fabricated nanoparticles exhibit excellent photo-absorption/discharge characteristics, suggesting that ZnSe nanoparticles can be alloyed without the need for organic solutions or high-temperature environments.

Bismuth vanadate (BiVO₄) is considered a potentially attractive candidate for the visible-light-driven photodegradation of organic pollutants. In an effort to enhance their photocatalytic activities, BiVO₄ nanofibers with controlled microstructures, grain sizes, and crystallinities are successfully prepared by electrospinning followed by a precisely controlled heat treatment. The structural features, morphologies, and photo-absorption performances of the asprepared samples are systematically investigated and can be readily controlled by varying the calcination temperature. From the physicochemical analysis results of the synthesized nanofiber, it is found that the nanofiber calcines at a lower temperature, shows a smaller crystallite size, and lower crystallinity. The photocatalytic degradation of rhodamine-B (RhB) reveals that the photocatalytic activity of the BiVO₄ nanofibers can be improved by a thermal treatment at a relatively low temperature because of the optimization of the conflicting characteristics, crystallinity, crystallite size, and microstructure. The photocatalytic activity of the nanofiber calcined at 350°C for the degradation of RhB under visible-light irradiation exhibits a greater photocatalytic activity than the nanofibers synthesized at 400°C and 450°C.

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• Design, synthesis, and characterization of a porous ceramic-supported CeO2 nanocatalyst for CO -free H2 evolution
  Jimin Lee, Minseob Lim, Tae Sung Kim, Kee-Ryung Park, Jong-Sik Lee, Hong-Baek Cho, Joo Hyun Park, Yong-Ho Choa
  Applied Surface Science.2021; 548: 149198.     CrossRef

ZrB₂ ceramic and ZrB₂ ceramic composites with the addition of SiC, WC, and SiC/WC are successfully synthesized by a spark plasma sintering method. During high-temperature oxidation, SiC additive form a SiO₂ amorphous outer scale layer and SiC-deplete ZrO₂ scale layer, which decrease the oxidation rate. WC addition forms WO₃ during the oxidation process to result in a ZrO₂/WO₃ liquid sintering layer, which is known to improve the antioxidation effect. The addition of SiC and WC to ZrB₂ reduces the oxygen effective diffusivity by one-fifth of that of ZrB₂. The addition of both SiC and WC shows the formation of a SiO₂ outer dense glass layer and ZrO₂/WO₃ layer so that the anti-oxidation effect is improved three times as much as that of ZrB₂. Therefore, SiC- and WC-added ZrB₂ has a lower two-order oxygen effective diffusivity than ZrB₂; it improves the anti-oxidation performance 3 times as much as that of ZrB₂.

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• Role of TiC and WC Addition on the Mechanism and Kinetics of Isothermal Oxidation and High-Temperature Stability of ZrB2–SiC Composites
  Pradyut Sengupta, Indranil Manna
  High Temperature Corrosion of Materials.2024; 101(S1): 57.     CrossRef

Piezoelectric ceramic specimens with the Pb(Mg_1/3Nb_2/3)_0.65Ti_0.35O₃ (PMN-PT) composition are prepared by the solid state reaction method known as the “columbite precursor” method. Moreover, the effects of the Li₂O-Bi₂O₃ additive on the microstructure, crystal structure, and piezoelectric properties of sintered PMN-PT ceramic samples are investigated. The addition of Li₂O-Bi₂O₃ lowers the sintering temperature from 1,200°C to 950°C. Moreover, with the addition of >5 wt.% additive, the crystal structure changes from tetragonal to rhombohedral. Notably, the sample with 3 wt.% additive exhibits excellent piezoelectric properties (d33 = 596 pC/N and Kp = 57%) and a sintered density of 7.92 g/cm³ after sintering at 950°C. In addition, the sample exhibits a curie temperature of 138.6°C at 1 kHz. Finally, the compatibility of the sample with a Cu electrode is examined, because the energy-dispersive X-ray spectroscopy data indicate the absence of interdiffusion between Cu and the ceramic material.

In this study, ultrasonic spray pyrolysis combined with salt-assisted decomposition, a process that adds sodium nitrate (NaNO₃) into a titanium precursor solution, is used to synthesize nanosized titanium dioxide (TiO₂) particles. The added NaNO₃ prevents the agglomeration of the primary nanoparticles in the pyrolysis process. The nanoparticles are obtained after a washing process, removing NaNO₃ and NaF from the secondary particles, which consist of the salts and TiO₂ nanoparticles. The effects of pyrolysis temperature on the size, crystallographic characteristics, and bandgap energy of the synthesized nanoparticles are systematically investigated. The synthesized TiO₂ nanoparticles have a size of approximately 2–10 nm a bandgap energy of 3.1–3.25 eV, depending on the synthetic temperature. These differences in properties affect the photocatalytic activities of the synthesized TiO₂ nanoparticles.

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• Microstructure and Sintering Behavior of Fine Tungsten Powders Synthesized by Ultrasonic Spray Pyrolysis
  Hyeonhui Jo, Jeong Hyun Kim, Young-In Lee, Young-Keun Jeong, Sung-Tag Oh
  Korean Journal of Metals and Materials.2021; 59(5): 289.     CrossRef

Over the last decade, the next generation’s ultra-high-temperature materials as an alternative to Nickel-based superalloys have been highlighted. Ultra-high-temperature materials based on refractory metals are one of several potential candidates. In particular, molybdenum alloys with small amounts of silicon and boron (Mo-Si-B alloys) have superior properties at high temperature. However, research related to Mo-Si-B alloys were mainly conducted by several developed countries but garnered little interest in Korea. Therefore, in this review paper, we introduce the development history of Mo-Si-B alloys briefly and discuss the properties, particularly the mechanical and oxidation properties of Mo-Si-B alloys. We also introduce the latest research trends of Mo-Si-B alloys based on the research paper. Finally, for domestic research related to this field, we explain why Mo-Si-B alloys should be developed and suggest the potential directions for Mo-Si-B alloys research.

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• Thermal Stability and Weight Reduction of Al0.75V2.82CrZr Refractory High Entropy Alloy Prepared Via Mechanical Alloying
  Minsu Kim, Hansung Lee, Byungmin Ahn
  journal of Korean Powder Metallurgy Institute.2023; 30(6): 478.     CrossRef
• Preparation and Structure of Chromium Coatings Doped with Diamond Nanoparticles Deposited Directly on a Monolithic Composite of Molybdenum and Aluminum
  V. P. Petkov, M. K. Aleksandrova, R. V. Valov, V. P. Korzhov, V. M. Kiiko, I. S. Zheltyakova
  Protection of Metals and Physical Chemistry of Surfaces.2023; 59(3): 396.     CrossRef
• A Review of Mo-Si Intermetallic Compounds as Ultrahigh-Temperature Materials
  Liang Jiang, Bin Zheng, Changsong Wu, Pengxiang Li, Tong Xue, Jiandong Wu, Fenglan Han, Yuhong Chen
  Processes.2022; 10(9): 1772.     CrossRef
• Heat-Resistant Molybdenum Borosilicate Alloys Hardened with Titanium Carbides: Mo–Si–B–TiC (Survey)
  I. L. Svetlov, O. G. Ospennikova, M. I. Karpov, Yu. V. Artemenko
  Inorganic Materials: Applied Research.2021; 12(4): 866.     CrossRef

The impact of different mixing methods and sintering temperatures on the microstructure and piezoelectric properties of PZNN-PZT ceramics is investigated. To improve the sinterability and piezoelectric properties of these ceramics, the composition of 0.13Pb((Zn_0.8Ni_0.2)_1/3Nb_2/3)O₃-0.87Pb(Zr_0.5Ti_0.5)O₃ (PZNN-PZT) containing a Pb-based relaxor component is selected. Two methods are used to create the powder for the PZNN-PZT ceramics. The first involves blending all source powders at once, followed by calcination. The second involves the preferential creation of columbite as a precursor, by reacting NiO with Nb₂O₅ powder. Subsequently, PZNN-PZT powder can be prepared by mixing the columbite powder, PbO, and other components, followed by an additional calcination step. All the PZNNPZT powder samples in this study show a nearly-pure perovskite phase. High-density PZNN-PZT ceramics can be fabricated using powders prepared by a two-step calcination process, with the addition of 0.3 wt% MnO2 at even relatively low sintering temperatures from 800°C to 1000°C. The grain size of the ceramics at sintering temperatures above 900°C is increased to approximately 3 μm. The optimized PZNN-PZT piezoelectric ceramics show a piezoelectric constant (d₃₃) of 360 pC/N, an electromechanical coupling factor (kp) of 0.61, and a quality factor (Q_m) of 275.

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• An Analysis of Edge Chipping in LiTaO3 Wafer Grinding Using a Scratch Test and FEA Simulation
  Haeseong Hwang, Seungho Han, Hyunseop Lee
  Lubricants.2023; 11(7): 297.     CrossRef
• A generalized rule for phase transition generated by additives in piezoelectric ceramics
  Jae-Min Cha, Young-Kook Moon, Jung-hwan Kim, Hyun-Ae Cha, Jong-Jin Choi, Byung-Dong Hahn, Seog-Young Yoon, Cheol-Woo Ahn
  Materials Today Communications.2023; 37: 107290.     CrossRef
• Low-Temperature Sintering Properties of Bi2O3 Doped PZT-5H Piezoelectric Ceramics
  Wanzi Mao, Qing Xu, Duanping Huang, Huajun Sun, Feng Zhang, Xiaobin Xie
  Journal of Electronic Materials.2023; 52(5): 3334.     CrossRef
• Effect of LiBiO2 on low-temperature sintering of PZT-PZNN ceramics
  Sung Cheul Hong, Shi Yeon Kim, Dong-Hun Yeo, Hyo-Soon Shin, Zee Hoon Park, Sahn Nahm
  Journal of the Korean Ceramic Society.2022; 59(5): 638.     CrossRef
• Two-Stage De-binding for Cu Electrode Application to PZT-PZNN Multilayer Actuator
  Sung Cheul Hong, Zeehoon Park, Dong-Hun Yeo, Hyo-Soon Shin, Sahn Nahm
  Transactions on Electrical and Electronic Materials.2022; 23(4): 348.     CrossRef

Porous metals demonstrate not only excessively low densities, but also novel physical, thermal, mechanical, electrical, and acoustic properties. Thus, porous metals exhibit exceptional performance, which are useful for diesel particulate filters, heat exchangers, and noise absorbers. In this study, SUS316L foam with 90% porosity and 3,000 μm pore size is successfully manufactured using the electrostatic powder coating (ESPC) process. The mean size of SUS316L powders is approximately 12.33 μm. The pore properties are evaluated using SEM and Archimedes. As the quantity of powder coating increases, pore size decreases from 2,881 to 1,356 μm. Moreover, the strut thickness and apparent density increase from 423.7 to 898.3 μm and from 0.278 to 0.840 g/cm³, respectively. It demonstrates that pore properties of SUS316L powder porous metal are controllable by template type and quantity of powder coating.

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• Fabrication and Pore Characteristics of Metal Powder Filters with a Cross-Sealed Honeycomb Shape Using Material Extrusion Additive Manufacturing
  Minji Kim, Min-Jeong Lee, Su-Jin Yun, Poong-Yeon Kim, Hyeon Ju Kim, Juyong Kim, Jung Woo Lee, Jung-Yeul Yun
  Journal of Powder Materials.2025; 32(4): 299.     CrossRef

Recent developments in the field of energy harvesting technology that convert ambient energy resources into electricity enable the use of self-powered energy systems in wearable and portable electronic devices without the need for additional external power sources. In particular, piezoelectric-effect-based flexible energy harvesters have drawn much attention because they can guarantee power generation from ubiquitous mechanical and vibrational movements. In response to demand for sustainable, permanent, and remote use of real-life personal electronics, many research groups have investigated flexible piezoelectric energy harvesters (f-PEHs) that employ nanoscaled piezoelectric materials such as nanowires, nanoparticles, nanofibers, and nanotubes. In those attempts, they have proven the feasibility of energy harvesting from tiny periodic mechanical deformations and energy utilization of f-PEH in commercial electronic devices. This review paper provides a brief overview of f-PEH devices based on piezoelectric nanomaterials and summarizes the development history, output performance, and applications.

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• Development and Characterization of Hafnium-Doped BaTiO3 Nanoparticle-Based Flexible Piezoelectric Devices
  HakSu Jang, Hyeon Jun Park, Gwang Hyeon Kim, Gyoung-Ja Lee, Jae-Hoon Ji, Donghun Lee, Young Hwa Jung, Min-Ku Lee, Changyeon Baek, Kwi-Il Park
  JOURNAL OF SENSOR SCIENCE AND TECHNOLOGY.2024; 33(1): 34.     CrossRef
• Enhanced Piezoelectric Performance of Composite Fibers Based on Lead-Free BCTZ Ceramics and P(VDF-TrFE) Piezopolymer for Self-Powered Wearable Sensors
  Sung Cheol Park, Chaeyoung Nam, Changyeon Baek, Min-Ku Lee, Gyoung-Ja Lee, Kwi-Il Park
  ACS Sustainable Chemistry & Engineering.2022; 10(43): 14370.     CrossRef
• A Comparison Study of Output Performance of Organic-Inorganic Piezoelectric Nanocomposite Made of Piezoelectric/Non-piezoelectric Polymers and BaTiO₃ Nanoparticles
  Dong Yeol Hyeon, Kwi-Il Park
  Journal of Korean Powder Metallurgy Institute.2019; 26(2): 119.     CrossRef
• Piezoelectric Flexible Energy Harvester Based on BaTiO3 Thin Film Enabled by Exfoliating the Mica Substrate
  Dong Yeol Hyeon, Kwi-Il Park
  Energy Technology.2019;[Epub]     CrossRef
• Piezoelectric Energy Harvesting from Two-Dimensional Boron Nitride Nanoflakes
  Gyoung-Ja Lee, Min-Ku Lee, Jin-Ju Park, Dong Yeol Hyeon, Chang Kyu Jeong, Kwi-Il Park
  ACS Applied Materials & Interfaces.2019; 11(41): 37920.     CrossRef

We report the feasibility of TaC production via self-propagating high temperature synthesis, and the influence of the initial green compact density on the final composite particle size. Experiments are carried out from a minimum pressure of 0.3 MPa, the pressure at which the initial green body becomes self-standing, up to 3 MPa, the point at which no further combustion occurs. The green density of the pellets varies from 29.99% to 42.97%, as compared with the theoretical density. The increase in green density decreases the powder size of TaC, and the smallest particle size is observed with 1.5 MPa, at 10.36 μm. Phase analysis results confirm the presence of the TaC phase only. In the range of 0.3-0.5 MPa, traces of unreacted Ta and C residues are detected. However, results also show the presence of only C residue in the matrix within the pressure range of 0.6-3.0 MPa.

Core/shell CdSe/ZnS quantum dots (QDs) are synthesized by a microfluidic reactor-assisted continuous reactor system. Photoluminescence and absorbance of synthesized CdSe/ZnS core/shell QDs are investigated by fluorescence spectrophotometry and online UV-Vis spectrometry. Three reaction conditions, namely; the shell coating reaction temperature, the shell coating reaction time, and the ZnS/CdSe precursor volume ratio, are combined in the synthesis process. The quantum yield of the synthesized CdSe QDs is determined for each condition. CdSe/ZnS QDs with a higher quantum yield are obtained compared to the discontinuous microfluidic reactor synthesis system. The maximum quantum efficiency is 98.3% when the reaction temperature, reaction time, and ZnS/CdSe ratio are 270°C, 10 s, and 0.05, respectively. Obtained results indicate that a continuous synthesis of the Core/shell CdSe/ZnS QDs with a high quantum efficiency could be achieved by isolating the reaction from the external environment.

In this study we manufacture a Ni-Cr-B-Si +WC/12Co composite coating layer on a Cu base material using a laser cladding (LC) process, and investigate the microstructural and mechanical properties of the LC coating and Ni electroplating layers (reference material). The initial powder used for the LC coating layer is a powder feedstock with an average particle size of 125 μm. To identify the microstructural and mechanical properties, OM, SEM, XRD, room and high temperature hardness, and wear tests are implemented. Microstructural observation of the initial powder and LC coating layer confirm the layer is composed mainly of γ-Ni phases and WC and Cr₂₃C₆ carbides. The measured hardness of the LC coating and Ni electroplating layers are 653 and 154 Hv, respectively. The hardness measurement from room up to high temperatures of 700°C result in a hardness decrease as the temperature increases, but the hardness of the LC coating layer is higher for all temperature conditions. Room temperature wear results show that the wear loss of the LC coating layer is 1/12 of the wear level of the Ni electroplating layer. The measured bond strength is also greater in the LC coating than the Ni electroplating.

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• Microstructure and Room Temperature Wear Properties of a Ni-Cr-B-Si-C Coating Layer Manufactured by the Laser Cladding Process
  Tae-Hoon Kang, Kyu-Sik Kim, Soon-Hong Park, Kee-Ahn Lee
  Korean Journal of Metals and Materials.2018; 56(6): 423.     CrossRef
• Microstructural and Wear Properties of WC-based and Cr₃C₂-based Cermet Coating Materials Manufactured with High Velocity Oxygen Fuel Process
  Yeon-Ji Kang, Gi-Su Ham, Hyung-Jun Kim, Sang-Hoon Yoon, Kee-Ahn Lee
  Journal of Korean Powder Metallurgy Institute.2018; 25(5): 408.     CrossRef

Synthesized monocrystalline nanodiamond (nD) particles are heat-treated at various temperatures to produce highly structured diamond crystals. The heat-treated nDs show different weight loss ratios during thermogravimetric analysis. The crystallinities of the heat-treated nDs are analyzed using Raman spectroscopy. The average particle sizes of the heat-treated nDs are measured by a dynamic light scattering (DLS) system and direct imaging observation methods. Moreover, individual dispersion behaviors of the heat-treated nD particles are investigated based on ultrasonic dispersion methods. The average particle sizes of the dispersed nDs according to the two different measurement methods show very similar size distributions. Thus, it is possible to produce highly crystallized nD powder particles by a heattreatment process, and the nD particles are relatively easy to disperse individually without any dispersant. The heattreated nDs can lead to potential applications such as in nanocomposites, quantum dots, and biomedical materials.

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• Two extreme crystal size scales of diamonds, large single crystal and nanocrystal diamonds: Synthesis, properties and their mutual transformation
  Yang Wang, Wei-hua Wang, Shi-lin Yang, Guo-yang Shu, Bing Dai, Jia-qi Zhu
  New Carbon Materials.2021; 36(3): 512.     CrossRef

This study investigates the oxidation properties of Fe-14Cr ferritic oxide-dispersion-strengthened (ODS) steel at various high temperatures (900, 1000, and 1100°C for 24 h). The initial microstructure shows that no clear structural change occurs even under high-temperature heat treatment, and the average measured grain size is 0.4 and 1.1 μm for the as-fabricated and heat-treated specimens, respectively. Y–Ti–O nanoclusters 10–50 nm in size are observed. High-temperature oxidation results show that the weight increases by 0.27 and 0.29 mg/cm² for the asfabricated and heat-treated (900°C) specimens, and by 0.47 and 0.50 mg/cm² for the as-fabricated and heat-treated (1000°C) specimens, respectively. Further, after 24 h oxidation tests, the weight increases by 56.50 and 100.60 mg/cm² for the as-fabricated and heat-treated (1100°C) specimens, respectively; the latter increase is approximately 100 times higher than that at 1000°C. Observation of the surface after the oxidation test shows that Cr₂O₃ is the main oxide on a specimen tested at 1000°C, whereas Fe₂O₃ and Fe₃O₄ phases also form on a specimen tested at 1100°C, where the weight increases rapidly. The high-temperature oxidation behavior of Fe-14Cr ODS steel is confirmed to be dominated by changes in the Cr₂O₃ layer and generation of Fe-based oxides through evaporation.

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• Microstructure and Wear Properties of Oxide Dispersion Strengthened Steel Powder Added Steel-Based Composite Material for Automotive Part
  Young-Kyun Kim, Jong-Kwan Park, Kee-Ahn Lee
  journal of Korean Powder Metallurgy Institute.2018; 25(1): 36.     CrossRef

In this study, we report the microstructure and the high-temperature oxidation behavior of Fe-Ni alloys by spark plasma sintering. Structural characterization is performed by scanning electron microscopy and X-ray diffraction. The oxidation behavior of Fe-Ni alloys is studied by means of a high-temperature oxidation test at 1000°C in air. The effect of Ni content of Fe-Ni alloys on the microstructure and on the oxidation characteristics is investigated in detail. In the case of Fe-2Ni and Fe-5Ni alloys, the microstructure is a ferrite (α) phase with body centered cubic (BCC) structure, and the microstructure of Fe-10Ni and Fe-20Ni alloys is considered to be a massive martensite (α’) phase with the same BCC structure as that of the ferrite phase. As the Ni content increases, the micro-Vickers hardness of the alloys also increases. It can also be seen that the oxidation resistance is improved by decreasing the thickness of the oxide film.

This study investigates the thermal shock property of a polycrystalline diamond compact (PDC) produced by a high-pressure, high-temperature (HPHT) sintering process. Three kinds of PDCs are manufactured by the HPHT sintering process using different particle sizes of the initial diamond powders: 8-16 μm (D50 = 4.3 μm), 10-20 μm (D50 = 6.92 μm), and 12-22 μm (D50 = 8.94 μm). The microstructure observation results for the manufactured PDCs reveal that elemental Co and W are present along the interface of the diamond particles. The fractions of Co and WC in the PDC increase as the initial particle size decreases. The manufactured PDCs are subjected to thermal shock tests at two temperatures of 780°C and 830°C. The results reveal that the PDC with a smaller particle size of diamond easily produces microscale thermal cracks. This is mainly because of the abundant presence of Co and WC phases along the diamond interface and the easy formation of Co-based (CoO, Co₃O₄) and W-based (WO₂) oxides in the PDC using smaller diamond particles. The microstructural factors for controlling the thermal shock property of PDC material are also discussed.

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• Effects of initial diamond particle size on the comprehensive mechanical properties of PDC
  Xueqi Wang, Jianbo Tu, Baochang Liu
  Ceramics International.2025; 51(8): 10433.     CrossRef
• High-impact-resistant polycrystalline diamond compact cutters with double working layers
  Xueqi Wang, Jianbo Tu, Baochang Liu
  Diamond and Related Materials.2025; 152: 111906.     CrossRef
• The Influence of the Binder Phase on the Properties of High-Pressure Sintered Diamond Polycrystals or Composites for Cutting Tool Applications
  Lucyna Jaworska
  Materials.2025; 18(3): 634.     CrossRef
• HPHT sintering and performance investigation of PDC with different interfacial geometry substrates for trimodal diamond particle size
  Jianbo Tu, Xueqi Wang, Haibo Zhang, Baochang Liu
  Ceramics International.2024; 50(11): 19074.     CrossRef
• HPHT sintering and performance investigation of PDC with high stacking density by dual particle size diamond formulations
  Jianbo Tu, Xueqi Wang, Baochang Liu
  International Journal of Refractory Metals and Hard Materials.2024; 124: 106802.     CrossRef

In this study, we investigate the effect of the diffusion barrier and substrate temperature on the length of carbon nanotubes. For synthesizing vertically aligned carbon nanotubes, thermal chemical vapor deposition is used and a substrate with a catalytic layer and a buffer layer is prepared using an e-beam evaporator. The length of the carbon nanotubes synthesized on the catalytic layer/diffusion barrier on the silicon substrate is longer than that without a diffusion barrier because the diffusion barrier prevents generation of silicon carbide from the diffusion of carbon atoms into the silicon substrate. The deposition temperature of the catalyst and alumina are varied from room temperature to 150°C, 200°C, and 250°C. On increasing the substrate temperature on depositing the buffer layer on the silicon substrate, shorter carbon nanotubes are obtained owing to the increased bonding force between the buffer layer and silicon substrate. The reason why different lengths of carbon nanotubes are obtained is that the higher bonding force between the buffer layer and the substrate layer prevents uniformity of catalytic islands for synthesizing carbon nanotubes.

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• A Study on Residual Powder Removing Technique of Multi-Layered Graphene Based on Graphene One-Step Transfer Process
  Chae-young Woo, Yeongsu Jo, Soon-kyu Hong, Hyung Woo Lee
  Journal of Korean Powder Metallurgy Institute.2019; 26(1): 11.     CrossRef
• Fabrication of robust, ultrathin and light weight, hydrophilic, PVDF-CNT membrane composite for salt rejection
  Vivek Dhand, Soon Kyu Hong, Luhe Li, Jong-Man Kim, Soo Hyung Kim, Kyong Yop Rhee, Hyung Woo Lee
  Composites Part B: Engineering.2019; 160: 632.     CrossRef

We report a facile method for preparing KIT-1 mesoporous silicates with two different macroporous structures by dual templating. As a template for macropores, polystyrene (PS) beads are assembled into uniform three dimensional arrays by ice templating, i.e., by growing ice crystals during the freezing process of the particle suspension. Then, the polymeric templates are directly introduced into the precursor-gel solution with cationic surfactants for templating the mesopores, which is followed by hydrothermal crystallization and calcination. Later, by burning out the PS beads and the surfactants, KIT-1 mesoporous silicates with macropores are produced in a powder form. The macroporous structures of the silicates can be controlled by changing the amount of EDTANa4 salt under the same templating conditions using the PS beads and inverse-opal or hollow structures can be obtained. This strategy to prepare mesoporous powders with controllable macrostructures is potentially useful for various applications especially those dealing with bulky molecules such as, catalysis, separation, drug carriers and environmental adsorbents.

A microfluidic reactor with computer-controlled programmable isocratic pumps and online detectors is employed as a combinatorial synthesis system to synthesize and analyze materials for fabricating CdSe quantum dots for various applications. Four reaction condition parameters, namely, the reaction temperature, reaction time, Cd/Se compositional ratio, and precursor concentration, are combined in synthesis condition sets, and the size of the synthesized CdSe quantum dots is determined for each condition. The average time corresponding to each reaction condition for obtaining the ultraviolet–visible absorbance and photoluminescence spectra is approximately 10 min. Using the data from the combinatorial synthesis system, the effects of the reaction conditions on the synthesized CdSe quantum dots are determined. Further, the data is used to determine the relationships between the reaction conditions and the CdSe particle size. This method should aid in determining and selecting the optimal conditions for synthesizing nanoparticles for diverse applications.

The organic binder-free paste for dye-sensitized solar cell (DSSC) has been investigated using peroxo titanium complex. The crystal structure of TiO₂ nanoparticles, morphology of TiO₂ film and electrical properties are analyzed by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Electrochemical Impedance Spectra (EIS), and solar simulator. The synthesized TiO₂ nanopowders by the peroxo titanium complex at 150, 300, 400°C, and 450°C have anatase phase and average crystal sizes are calculated to be 4.2, 13.7, 16.9, and 20.9 nm, respectively. The DSSC prepared by the peroxo titanium complex binder have higher V_oc and lower J_sc values than that of the organic binder. It can be attributed to improvement of sintering properties of TCO/TiO₂ and TiO₂/TiO₂ interface and to formation of agglomerate by the nanoparticles. As a result, we have investigated the organic binder-free paste and 3.178% conversion efficiency of the DSSC at 450°C.

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• Development of Eco-Friendly Ag Embedded Peroxo Titanium Complex Solution Based Thin Film and Electrical Behaviors of Resistive Random Access Memory
  Won Jin Kim, Jinho Lee, Ryun Na Kim, Donghee Lee, Woo-Byoung Kim
  Korean Journal of Materials Research.2024; 34(3): 152.     CrossRef
• Development of eco-friendly thin film manufacturing process using poeroxo titanium complex solution and potential for resistive random access memory
  Jinho Lee, Ryun Na Kim, Kee-Ryung Park, Woo-Byoung Kim
  Applied Surface Science.2021; 562: 150170.     CrossRef
• Preparation of ultra-thin TiO2 shell by peroxo titanium complex (PTC) solution-based green surface modification, and photocatalytic activity of homo-core/shell TiO2
  Jinho Lee, Jiyong Hwang, Hyunsu Park, Tohru Sekino, Woo-Byoung Kim
  Applied Surface Science.2021; 540: 148399.     CrossRef
• Effects of Annealing Temperature on the Crystal Structure, Morphology, and Optical Properties of Peroxo-Titanate Nanotubes Prepared by Peroxo-Titanium Complex Ion
  Hyunsu Park, Tomoyo Goto, Sunghun Cho, Soo Wohn Lee, Masato Kakihana, Tohru Sekino
  Nanomaterials.2020; 10(7): 1331.     CrossRef
• Study on thermal behavior of Ammonium Hexafluofide Titanate for Synthesis of TiO2 Powders
  Duk-Hee Lee, Jae-Ryang Park, Chan-Gi Lee, Kyung-Soo Park, Hyeon-Mo Kim
  Journal of Korean Powder Metallurgy Institute.2016; 23(5): 353.     CrossRef

Perforated polygonal cobalt oxide (CO₃O₄) is synthesized using electrospinning and a hydrothermal method followed by the removal of a carbon nanofiber (CNF) template. To investigate their formation mechanism, thermogravimetric analysis, field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Xray photoelectron spectroscopy are examined. To obtain the optimum condition of perforated polygonal CO₃O₄, we prepare three different weight ratios of the Co precursor and the CNF template: sample A (Co precursor:CNF template- 10:1), sample B (Co precursor:CNF template-3.2:1), and sample C (Co precursor:CNF template-2:1). Among them, sample A exhibits the perforated polygonal CO₃O₄ with a thin carbon layer (5.7-6.2 nm) owing to the removal of CNF template. However, sample B and sample C synthesized perforated round CO₃O₄ and destroyed CO₃O₄ powders, respectively, due to a decreased amount of Co precursor. The increased amount of the CNF template prevents the formation of polygonal CO₃O₄. For sample A, the optimized weight ratio of the Co precursor and CNF template may be related to the successful formation of perforated polygonal CO₃O₄. Thus, perforated polygonal CO₃O₄ can be applied to electrode materials of energy storage devices such as lithium ion batteries, supercapacitors, and fuel cells.

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• Synthesis of Nitrogen Doped Protein Based Carbon as Pt Catalysts Supports for Oxygen Reduction Reaction
  Young-geun Lee, Geon-hyeong An, Hyo-Jin Ahn
  Korean Journal of Materials Research.2018; 28(3): 182.     CrossRef
• Electrochemical Behavior of Well-dispersed Catalysts on Ruthenium Oxide Nanofiber Supports
  Geon-Hyoung An, Hyo-Jin Ahn
  Journal of Korean Powder Metallurgy Institute.2017; 24(2): 96.     CrossRef

MgB₂ bulk superconductors are synthesized by the solid state reaction of (MgB₄+xMg) precursors with excessive Mg compositions (x=1.0, 1.4, 2.0 and 2.4). The MgB₄ precursors are synthesized using (Mg+B) powders. The secondary phases (MgB₄ and MgO) present in the synthesized MgB₄ are removed by HNO₃ leaching. It is found that the formation reaction of MgB₂ is accelerated when Mg excessive compositions are used. The magnetization curves of Mg1+xB₂ samples show that the transition from the normal state to the superconducting state of the Mg excessive samples with x=0.5 and x=0.7 are sharper than that of MgB₂. The highest J_c-B curve at 5 K and 20 K is achieved for x=0.5. Further addition of Mg decreases the J_c owing to the formation of more pores in the MgB₂ matrix and smaller volume fraction of MgB₂.

The GaN-powder scrap generated in the manufacturing process of LED contains significant amounts of gallium. This waste can be an important resource for gallium through recycling of scraps. In the present study, the influence of annealing temperatures on the structural properties of GaN powder was investigated when the waste was recycled through the mechanochemical oxidation process. The annealing temperature varied from 200°C to 1100°C and the changes in crystal structure and microstructure were studied. The annealed powder was characterized using various analytical tools such as TGA, XRD, SEM, and XRF. The results indicate that GaN structure was fully changed to Ga₂O₃ structure when annealed above 900°C for 2 h. And, as the annealing temperature increased, crystallinity and particle size were enhanced. The increase in particle size of gallium oxide was possibly promoted by powder-sintering which merged particles to larger than 50 nm.

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• High-temperature thermo-mechanical behavior of functionally graded materials produced by plasma sprayed coating: Experimental and modeling results
  Kang Hyun Choi, Hyun-Su Kim, Chang Hyun Park, Gon-Ho Kim, Kyoung Ho Baik, Sung Ho Lee, Taehyung Kim, Hyoung Seop Kim
  Metals and Materials International.2016; 22(5): 817.     CrossRef

Vertically oriented nickel nanowire arrays with a different diameter and length are synthesized in porous anodic aluminium oxide templates by an electrodeposition method. The pore diameters of the templates are adjusted by controlling the anodization conditions and then they are utilized as templates to grow nickel nanowire arrays. The nickel nanowires have the average diameters of approximately 25 and 260 nm and the crystal structure, morphology and microstructure of the nanowires are systematically investigated using XRD, FE-SEM and TEM analysis. The nickel nanowire arrays show a magnetic anisotropy with the easy axis parallel to the nanowires and the coercivity and remanence enhance with decreasing a wire diameter and increasing a wire length.

In this study, ternary compound Max Phase Ti₂AlC material was mixed by 3D ball milling as a function of ball milling time. More than 99.5 wt% pure Ti₂AlC was synthesized by using spark plasma sintering method at 1000, 1100, 1200, and 1300°C for 60 min. The material characteristics of synthesized samples were examined with relative density, hardness, and electrical conductivity as a function of sintering temperature. The phase composition of bulk was identified by X-ray diffraction. On the basis of FE-SEM result, a terraced structures which consists of several laminated layers were observed. And Ti₂AlC bulk material obtained a vickers hardness of 5.1 GPa at the sintering temperature of 1100°C.

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• Synthesis and reaction path of Ti‐Al‐C MAX phases by reaction with Ti‐Al intermetallic compounds and TiC
  Hojun Lee, Si Yeon Kim, Young‐In Lee, Jongmin Byun
  Journal of the American Ceramic Society.2023; 106(12): 7230.     CrossRef

The porous metals are known as relatively excellent characteristic such as large surface area, light, lower heat capacity, high toughness and permeability. The Fe-Cr-Al alloys have high corrosion resistance, heat resistance and chemical stability for high temperature applications. And then many researches are developed the Fe-Cr-Al porous metals for exhaust gas filter, hydrogen reformer catalyst support and chemical filter. In this study, the Fe-Cr-Al porous metals are developed with Fe-22Cr-6Al(wt) powder using powder compaction method. The mean size of Fe-22Cr-6Al(wt) powders is about 42.69 μm. In order to control pore size and porosity, Fe-Cr-Al powders are sintered at 1200~1450°C and different sintering maintenance as 1~4 hours. The powders are pressed on disk shapes of 3 mm thickness using uniaxial press machine and sintered in high vacuum condition. The pore properties are evaluated using capillary flow porometer. As sintering temperature increased, relative density is increased from 73% to 96% and porosity, pore size are decreased from 27 to 3.3%, from 3.1 to 1.8 μm respectively. When the sintering time is increased, the relative density is also increased from 76.5% to 84.7% and porosity, pore size are decreased from 23.5% to 15.3%, from 2.7 to 2.08 μm respectively.

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• Synthesis and Magnetic Hysteresis Properties of an Aluminum-Doped Isotropic Hard-Magnetic Fe–Cr–Co Powder Alloy
  A. S. Ustyukhin, V. A. Zelensky, I. M. Milyaev, M. I. Alymov, A. A. Ashmarin, A. B. Ankudinov, K. V. Sergienko
  Inorganic Materials: Applied Research.2024; 15(2): 480.     CrossRef
• Fabrication of a Porous Ni-Based Metal with a Multi-pore Structure by a Screen Printing Process
  Yu-Jeong Yi, Min-Jeong Lee, Jung-Yeul Yun, Byoung-Kee Kim
  Metals and Materials International.2019; 25(5): 1272.     CrossRef

Silicon carbide(SiC) layer is particularly important tri-isotropic (TRISO) coating layers because it acts as a miniature pressure vessel and a diffusion barrier to gaseous and metallic fission products in the TRISO coated particle. The high temperature deposition of SiC layer normally performed at 1500-1650°C has a negative effect on the property of IPyC layer by increasing its anisotropy. To investigate the feasibility of lower temperature SiC deposition, the influence of deposition temperature on the property of SiC layer are examined in this study. While the SiC layer coated at 1500°C obtains nearly stoichiometric composition, the composition of the SiC layer coated at 1300-1400°C shows discrepancy from stoichiometric ratio(1:1). 3-7 μm grain size of SiC layer coated at 1500°C is decreased to sub-micrometer (<1 μm) -2 μm grain size when coated at 1400°C, and further decreased to nano grain size when coated at 1300- 1350°C. Moreover, the high density of SiC layer (≥3.19 g/cm³) which is easily obtained at 1500°C coating is difficult to achieve at lower temperature owing to nano size pores. the density is remarkably decreased with decreasing SiC deposition temperature.

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• High-temperature thermo-mechanical behavior of functionally graded materials produced by plasma sprayed coating: Experimental and modeling results
  Kang Hyun Choi, Hyun-Su Kim, Chang Hyun Park, Gon-Ho Kim, Kyoung Ho Baik, Sung Ho Lee, Taehyung Kim, Hyoung Seop Kim
  Metals and Materials International.2016; 22(5): 817.     CrossRef

In this study, nanocrystalline Cu-Ni bulk materials with various compositions were cold compacted by a shock compaction method using a single-stage gas gun system. Since the oxide layers on powder surface disturbs bonding between powder particles during the shock compaction process, each nanopowder was hydrogen-reduced to remove the oxide layers. X-ray peak analysis shows that hydrogen reduction successfully removed the oxide layers from the nano powders. For the shock compaction process, mixed powder samples with various compositions were prepared using a roller mixer. After the shock compaction process, the density of specimens increased up to 95% of the relative density. Longitudinal cross-sections of the shock compacted specimen demonstrates that a boundary between two powders are clearly distinguished and agglomerated powder particles remained in the compacted bulk. Internal crack tended to decrease with an increase in volumetric ratio of nano Cu powders in compacted bulk, showing that nano Cu powders has a higher coherency than nano Ni powders. On the other hand, hardness results are dominated by volume fraction of the nano Ni powder. The crystalline size of the shock compacted bulk materials was greatly reduced from the initial powder crystalline size since the shock wave severely deformed the powders.

A high temperature dilatometer attached to a graphite furnace is built and used to study the sintering behavior of B₄C. Pristine and carbon doped B₄C compacts are sintered at various soaking temperatures and their shrinkage profiles are detected simultaneously using the dilatometer. Carbon additions enhance the sinterability of B₄C with sintering to more than 97% of the theoretical density, while pristine B₄C compacts could not be sintered above 91% due to particle coarsening. The shrinkage profiles of B₄C reveal that the effect of carbon on the sinterability of B₄C can be seen mostly below 1950°C. The high temperature dilatometer delivers very useful information which is impossible to obtain with conventional furnaces.

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• Application of rate-controlled sintering into the study of sintering behavior of boron carbide
  Hyukjae Lee
  Journal of the Korean Crystal Growth and Crystal Technology.2015; 25(1): 6.     CrossRef

Fe-Cr-Al powder porous metal was manufactured by using new electro-spray process. First, ultra-fine fecralloy powders were produced by using the submerged electric wire explosion process. Evenly distributed colloid (0.05~0.5% powders) was dispersed on Polyurethane foam through the electro-spray process. And then degreasing and sintering processes were conduced. In order to examine the effect of cell size (200 μm, 450 μm, 500 μm) in process, pre-samples were sintered for two hours at temperature of 1450°C, in H₂ atmospheres. A 24-hour thermo gravimetric analysis test was conducted at 1000°C in a 79% N₂ + 21% O₂ to investigate the high temperature oxidation behavior of powder porous metal. The results of the high temperature oxidation tests showed that oxidation resistance increased with increasing cell size. In the 200 μm porous metal with a thinner strut and larger specific surface area, the depletion of the stabilizing elements such as Al and Cr occurred more quickly during the high-temperature oxidation compared with the 450, 500 μm porous metals.

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• Fabrication and Mechanical Properties of Open‐Cell Austenitic Stainless Steel Foam by Electrostatic Powder Spraying Process
  Tae-Hoon Kang, Kyu-Sik Kim, Jung-Yeul Yun, Min-Jeong Lee, Kee-Ahn Lee
  Advanced Engineering Materials.2020;[Epub]     CrossRef
• Microstructure and High Temperature Oxidation Behaviors of Fe-Ni Alloys by Spark Plasma Sintering
  Chae Hong Lim, Jong Seok Park, Sangsun Yang, Jung-Yeul Yun, Jin Kyu Lee
  Journal of Korean Powder Metallurgy Institute.2017; 24(1): 53.     CrossRef
• Effect of Al2O3 Inter-Layer Grown on FeCrAl Alloy Foam to Improve the Dispersion and Stability of NiO Catalysts
  유진 이, 본율 구, 성호 백, 만호 박, 효진 안
  Korean Journal of Materials Research.2015; 25(8): 391~397.     CrossRef

In this study, nanocrystalline nickel powders were cold compacted by a dynamic compaction method using a single-stage gas gun system. A bending test was conducted to measure the bonding strengths of the compacted regions and microstructures of the specimen were analyzed using a scanning electron microscopy. The specimen was separated into two parts by a horizontal crack after compaction. Density test shows that the powder compaction occurred only in the upper part of the specimen. Brittle fracture was occurred during the bending test of the compact sample. Dispersion of shock energy due to spalling highly affected the bonding status of the nanocrystalline nickel powder.