Tin dioxide nanoparticles are prepared using a newly developed synthesis method of plasma-assisted electrolysis. A high voltage is applied to the tin metal plate to apply a high pressure and temperature to the synthesized oxide layer on the metal surface, producing nanoparticles in a low concentration of sulfuric acid. The particle size, morphology, and size distribution is controlled by the concentration of electrolytes and frequency of the power supply. The as-prepared powder of tin dioxide nanoparticles is used to fabricate a gas sensor to investigate the potential application. The particle-based gas sensor exhibits a short response and recovery time. There is sensitivity to the reduction gas for the gas flowing at rates of 50, 250, and 500 ppm of H₂S gas.

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• Effects of porosity and particle size on the gas sensing properties of SnO2 films
  Min Ah Han, Hyun-Jong Kim, Hee Chul Lee, Jin-Seong Park, Ho-Nyun Lee
  Applied Surface Science.2019; 481: 133.     CrossRef

In this study, Bi-Sb-Te thermoelectric materials are produced by mechanical alloying (MA) and spark plasma sintering (SPS). To examine the influence of the milling atmosphere on the microstructure and thermo-electric (TE) properties, a p-type Bi-Sb-Te composite powder is mechanically alloyed in the presence of argon and air atmospheres. The oxygen content increases to 55% when the powder is milled in the air atmosphere, compared with argon. All grains are similar in size and uniformly, distributed in both atmospheric sintered samples. The Seebeck coefficient is higher, while the electrical conductivity is lower in the MA (Air) sample due to a low carrier concentration compared to the MA (Ar) sintered sample. The maximum figure of merit (ZT) is 0.91 and 0.82 at 350 K for the MA (Ar) and MA (Air) sintered samples, respectively. The slight enhancement in the ZT value is due to the decrease in the oxygen content during the MA (Ar) process. Moreover, the combination of mechanical alloying and SPS process shows a higher hardness and density values for the sintered samples.

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• Advancement of thermoelectric performances through the dispersion of expanded graphene on p-type BiSbTe alloys
  Eun-Ha Go, Rathinam Vasudevan, Babu Madavali, Peyala Dharmaiah, Min-Woo Shin, Sung Ho Song, Soon-Jik Hong
  Powder Metallurgy.2023; 66(5): 722.     CrossRef
• Influence of milling atmosphere on the structure and magnetic properties of mechanically alloyed Fe40Co30Ni30
  Alex Abraham Paul, Anuj Rathi, Ganesh Varma Thotakura, Tanjore V. Jayaraman
  Materials Chemistry and Physics.2021; 258: 123897.     CrossRef
• Enhancement of mechanical properties and thermoelectric performance of spark plasma sintered P-type Bismuth Telluride by powder surface oxide reduction
  Ahmed A. Abdelnabi, Vickram Lakhian, Joseph R. McDermid, Yu-Chih Tseng, James S. Cotton
  Journal of Alloys and Compounds.2021; 858: 157657.     CrossRef
• Solid solution evolution during mechanical alloying in Cu-Nb-Al compounds
  Kaouther Zaara, Mahmoud Chemingui, Virgil Optasanu, Mohamed Khitouni
  International Journal of Minerals, Metallurgy, and Materials.2019; 26(9): 1129.     CrossRef

Ceramic powder, such as MgO, is added as a binder to prepare the green compacts of molten salts of an electrolyte for a thermal battery. Despite the addition of a binder, when the thickness of the electrolyte decreases to improve the battery performance, the problem with the unintentional short circuit between the anode and cathode still remains. To improve the current powder molding method, a new type of electrolyte separator with porous MgO preforms is prepared and characteristics of the thermal battery are evaluated. A Spherical PMMA polymer powder is added as a pore-forming agent in the MgO powder, and an organic binder is used to prepare slurry appropriate for tape casting. A porous MgO preform with 300 μm thickness is prepared through a binder burnout and sintering process. The particle size of the starting MgO powder has an effect, not on the porosity of the porous MgO preform, but on the battery characteristics. The porosity of the porous MgO preforms is controlled from 60 to 75% using a pore-forming agent. The batteries prepared using various porosities of preforms show a performance equal to or higher than that of the pellet-shaped battery prepared by the conventional powder molding method.

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

Microstructure, electric, and thermal properties of the Ta-Cu composite is evaluated for the application in electric contact materials. This material has the potential to be used in a medium for a high current range of current conditions, replacing Ag-MO, W, and WC containing materials. The optimized SPS process conditions are a temperature of 900°C for a 5 min holding time under a 30 MPa mechanical pressure. Comparative research is carried out for the calculated and actual values of the thermal and electric properties. The range of actual thermal and electric properties of the Ta-Cu composite are 50~300W/mk and 10~90 %IACS, respectively, according to the compositional change of the 90 to 10 wt% Ta-Cu system. The results related to the electric contact properties, suggest that less than 50 wt% of Ta compositions are possible in applications of electric contact materials.

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• Formation mechanism, microstructural features and dry-sliding behaviour of “Bronze/WC carbide” composite synthesised by atmospheric pulsed-plasma deposition
  V.G. Efremenko, Yu.G. Chabak, V.I. Fedun, K. Shimizu, T.V. Pastukhova, I. Petryshynets, A.M. Zusin, E.V. Kudinova, B.V. Efremenko
  Vacuum.2021; 185: 110031.     CrossRef

The effect of the mixing method on the characteristics of hybrid-structure W powder with nano and micro sizes is investigated. Fine WO₃ powders with sizes of ~0.6 μm, prepared by ball milling for 10 h, are mixed with pure W powder with sizes of 12 μm by various mixing process. In the case of simple mixing with ball-milled WO₃ and micro sized W powders, WO₃ particles are locally present in the form of agglomerates in the surface of large W powders, but in the case of ball milling, a relatively uniform distribution of WO₃ particles is exhibited. The microstructural observation reveals that the ball milled WO₃ powder, heat-treated at 750°C for 1 h in a hydrogen atmosphere, is fine W particles of ~200 nm or less. The powder mixture prepared by simple mixing and hydrogen reduction exhibits the formation of coarse W particles with agglomeration of the micro sized W powder on the surface. Conversely, in the powder mixture fabricated by ball milling and hydrogen reduction, a uniform distribution of fine W particles forming nano-micro sized hybrid structure is observed.

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• The Efficiency of Radiation Shielding Sheet to Reduce Radiation Exposure during C-arm Fluoroscopy
  Hosang Jeon, Won Chul Shin, Hee Yun Seol, Yongkan Ki, Kyeong Baek Kim, Ki Seok Choo, Sang Don Lee, Suk-Woong Kang
  Journal of the Korean Fracture Society.2023; 36(4): 111.     CrossRef
• Facile phosphorus-embedding into SnS2 using a high-energy ball mill to improve the surface kinetics of P-SnS2 anodes for a Li-ion battery
  Hongsuk Choi, Seungmin Lee, KwangSup Eom
  Applied Surface Science.2019; 466: 578.     CrossRef
• Hydrogen reduction behavior and microstructural characteristics of WO3 and WO3-NiO powders
  Hyunji Kang, Young-Keun Jeong, Sung-Tag Oh
  International Journal of Refractory Metals and Hard Materials.2019; 80: 69.     CrossRef
• Fabrication of Densified W-Ti by Reaction Treatment and Spark Plasma Sintering of WO3-TiH2 Powder Mixtures
  Hyunji Kang, Heun Joo Kim, Ju-Yeon Han, Yunju Lee, Young-Keun Jeong, Sung-Tag Oh
  Korean Journal of Materials Research.2018; 28(9): 511.     CrossRef

Ni wires with a diameter and length of 0.4 and 100 mm, respectively, and a purity of 99.9% are electrically exploded at 25 cycles per minute. The Ni nanopowders are successfully synthesized by a pulsed wire evaporation (PWE) method, in which Ar gas is used as the ambient gas. The characterization of the nanopowders is carried out using X-ray diffraction (XRD) and a high-resolution transmission electronmicroscope (HRTEM). The Ni nanopowders are classified for a multilayer ceramic condenser (MLCC) application using a type two Air-Centrifugal classifier (model: CNI, MP-250). The characterization of the classified Ni nanopowders are carried out using a scanning electron microscope (SEM) and particle size analysis (PSA) to observe the distribution and minimum classification point (minimum cutting point) of the nanopowders.

Solder paste is widely used as a conductive adhesive in the electronics industry. In this paper, nano and microsized mixed lead-free solder powder (Sn-Ag-Cu) is used to manufacture solder paste. The purpose of this paper is to improve the storage stability using different types of solvents that are used in fabricating the solder paste. If a solvent of sole acetate is used, the nano sized solder powder and organic acid react and form a Sn-Ag-Cu malonate. These formed malonates create fatty acid soaps. The fatty acid soaps absorb the solvents and while the viscosity of the solder paste rises, the storage stability and reliability decrease. When ethylene glycol, a dihydric alcohol, is used the fatty acid soaps and ethylene glycol react, preventing the further creation of the fatty acid soaps. The prevention of gelation results in an improvement in the solder paste storage ability.

The addition of a large amount of alloying elements reduces the compactibility and increases the compacting pressure, thereby shortening the life of the compacting die and increasing the process cost of commercial PM steel. In this study, the characteristic changes of Fe-Mo-P, Fe-Mn-P, and Fe-Mo-Mn-P alloys are investigated according to the Si contents to replace the expensive elements, such as Ni. All compacts with different Si contents are fabricated with the same green densities of 7.0 and 7.2 g/cm³. The transverse rupture strength (TRS) and sintered density are measured using the specimens obtained through the sintering process. The sintered density tends to decrease, whereas the TRS increases as the Si content increases. The TRS of the sintered specimen compacted with 7.2 g/cm³ is twice as high as that compacted with 7.0 g/cm³.

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• The Effects of Si or Sn on the Sintered Properties of Fe-(Mo,Mn)-P Lean alloy
  Woo-Young Jung, Jin-Uk Ok, Dong-Kyu Park, In-Shup Ahn
  Journal of Korean Powder Metallurgy Institute.2018; 25(4): 302.     CrossRef

A Nanosized WO₃ and CuO powder mixture is prepared using novel high-energy ball milling in a bead mill to obtain a W-Cu nanocomposite powder, and the effect of milling time on the structural characteristics of WO₃-CuO powder mixtures is investigated. The results show that the ball-milled WO₃-CuO powder mixture reaches at steady state after 10 h milling, characterized by the uniform and narrow particle size distribution with primary crystalline sizes below 50 nm, a specific surface area of 37 m²/g, and powder mean particle size (D₅₀) of 0.57 μm. The WO₃-CuO powder mixtures milled for 10 h are heat-treated at different temperatures in H₂ atmosphere to produce W-Cu powder. The XRD results shows that both the WO₃ and CuO phases can be reduced to W and Cu phases at temperatures over 700°C. The reduced W-Cu nanocomposite powder exhibits excellent sinterability, and the ultrafine W-Cu composite can be obtained by the Cu liquid phase sintering process.