A conductive additive is prepared by dispersing multi-walled carbon nanotubes (MWCNTs) on Cu powder by mechanical milling and is distributed in epoxy to enhance its electrical conductivity. During milling, the MWCNTs are dispersed and partially embedded on the surface of the Cu powder to provide electrically conductive pathways within the epoxy-based composite. The degree of dispersion of the MWCNTs is controlled by varying the milling medium and the milling time. The MWCNTs are found to be more homogeneously dispersed when solvents (particularly, non-polar solvent, i.e., NMP) are used. MWCNTs gradually disperse on the surface of Cu powder because of the plastic deformation of the ductile Cu powder. However, long-time milling is found to destroy the molecular structure of MWCNTs, instead of effectively dispersing the MWCNTs more uniformly. Thus, the epoxy composite film fabricated in this study exhibits a higher electrical conductivity than 1.1 S/cm.

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• Effects of Morphologies of Carbon Nanomaterials on Conductivity of Composites Containing Copper/Carbon Nanomaterial Hybrid Fillers
  Yeonjoo Lee, Sung-uk Hong, Hyunjoo Choi
  Journal of Korean Powder Metallurgy Institute.2018; 25(5): 435.     CrossRef

In this study, an experiment is performed to recover the Li in Li₂CO₃ phase from the cathode active material NMC (LiNiCoMnO₂) in waste lithium ion batteries. Firstly, carbonation is performed to convert the LiNiO, LiCoO, and Li₂MnO₃ phases within the powder to Li₂CO₃ and NiO, CoO, and MnO. The carbonation for phase separation proceeds at a temperature range of 600°C~800°C in a CO₂ gas (300 cc/min) atmosphere. At 600~700°C, Li₂CO₃ and NiO, CoO, and MnO are not completely separated, while Li and other metallic compounds remain. At 800 °C, we can confirm that LiNiO, LiCoO, and Li₂MnO₃ phases are separated into Li₂CO₃ and NiO, CoO, and MnO phases. After completing the phase separation, by using the solubility difference of Li₂CO₃ and NiO, CoO, and MnO, we set the ratio of solution (distilled water) to powder after carbonation as 30:1. Subsequently, water leaching is carried out. Then, the Li₂CO₃ within the solution melts and concentrates, while NiO, MnO, and CoO phases remain after filtering. Thus, Li₂CO₃ can be recovered.

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• Influence of Flow-Gas Composition on Reaction Products of Thermally Treated NMC Battery Black Mass
  Christin Stallmeister, Bernd Friedrich
  Metals.2023; 13(5): 923.     CrossRef
• Holistic Investigation of the Inert Thermal Treatment of Industrially Shredded NMC 622 Lithium-Ion Batteries and Its Influence on Selective Lithium Recovery by Water Leaching
  Christin Stallmeister, Bernd Friedrich
  Metals.2023; 13(12): 2000.     CrossRef
• Environmentally Friendly Recovery of Lithium from Lithium–Sulfur Batteries
  Lilian Schwich, Bernd Friedrich
  Metals.2022; 12(7): 1108.     CrossRef
• Early-Stage Recovery of Lithium from Tailored Thermal Conditioned Black Mass Part I: Mobilizing Lithium via Supercritical CO2-Carbonation
  Lilian Schwich, Tom Schubert, Bernd Friedrich
  Metals.2021; 11(2): 177.     CrossRef
• Exploring a green route for recycling spent lithium-ion batteries: Revealing and solving deep screening problem
  Jiadong Yu, Quanyin Tan, Jinhui Li
  Journal of Cleaner Production.2020; 255: 120269.     CrossRef

A lean alloy is defined as a low alloy steel that minimizes the content of the alloying elements, while maintaining the characteristics of the sintered alloy. The purpose of this study is to determine the change in microstructure and mechanical properties due to the addition of silicon or tin in Fe-Mo-P, Fe-Mn-P, and Fe-Mo-Mn-P alloys. Silicon- or tin-added F-Mo-P, Fe-Mn-P, and Fe-Mo-Mn-P master alloys were compacted at 700 MPa and subsequently sintered under a H₂-N₂ atmosphere at 1120°C. The sintered density of three alloy systems decreases under the same compacting pressure due to dimensional expansion with increasing Si content. As the diffusion rate in the Fe-P-Mo system is higher than that in the Fe-P-Mn system, the decrease in the sintered density is the largest in the Fe-PMn system. The sintered density of Sn added alloys does not change with the increasing Sn content due to the effect of non-dimensional changes. However, the effect of Si addition on the transverse rupture strengthening enhancement is stronger than that of Sn addition in these lean alloys.

In the present work, we synthesize nano-sized ZnO, SnO₂, and TiO₂ powders by hydrothermal reaction using metal chlorides. We also examine the energy-storage characteristics of the resulting materials to evaluate the potential application of these powders to dye-sensitized solar cells. The control of processing parameters such as pressure, temperature, and the concentration of aqueous solution results in the formation of a variety of powder morphologies with different sizes. Nano-rod, nano-flower, and spherical powders are easily formed with the present method. Heat treatment after the hydrothermal reaction usually increases the size of the powder. At temperatures above 1000°C, a complete collapse of the shape occurs. With regard to the capacity of DSSC materials, the hydrothermally synthesized TiO₂ results in the highest current density of 9.1 mA/cm² among the examined oxides. This is attributed to the fine particle size and morphology with large specific surface area.

Composites of P25 TiO₂ and hexagonal WO₃ nanorods are synthesized through ball-milling in order to study photocatalytic properties. Various composites of TiO₂/WO₃ are prepared by controlling the weight percentages (wt%) of WO₃, in the range of 1–30 wt%, and milling time to investigate the effects of the composition ratio on the photocatalytic properties. Scanning electron microscopy, x-ray diffraction, and transmission electron microscopy are performed to characterize the structure, shape and size of the synthesized composites of TiO₂/WO₃. Methylene blue is used as a test dye to analyze the photocatalytic properties of the synthesized composite material. The photocatalytic activity shows that the decomposition efficiency of the dye due to the photocatalytic effect is the highest in the TiO₂/WO₃ (3 wt%) composite, and the catalytic efficiency decreases sharply when the amount of WO₃ is further increased. As the amount of WO₃ added increases, dye-removal by adsorption occurs during centrifugation, instead of the decomposition of dyes by photocatalysts. Finally, TiO₂/WO₃ (3 wt%) composites are synthesized with various milling times. Experimental results show that the milling time has the best catalytic efficiency at 30 min, after which it gradually decreases. There is no significant change after 1 hour.

The hydrogen reduction behavior of MoO₃-CuO powder mixture for the synthesis of homogeneous Mo-20 wt% Cu composite powder is investigated. The reduction behavior of ball-milled powder mixture is analyzed by XRD and temperature programmed reduction method at various heating rates in Ar-10% H₂ atmosphere. The XRD analysis of the heat-treated powder at 300°C shows Cu, MoO₃, and Cu₂MoO₅ phases. In contrast, the powder mixture heated at 400°C is composed of Cu and MoO₂ phases. The hydrogen reduction kinetic is evaluated by the amount of peak shift with heating rates. The activation energies for the reduction, estimated by the slope of the Kissinger plot, are measured as 112.2 kJ/mol and 65.2 kJ/mol, depending on the reduction steps from CuO to Cu and from MoO₃ to MoO₂, respectively. The measured activation energy for the reduction of MoO₃ is explained by the effect of pre-reduced Cu particles. The powder mixture, hydrogen-reduced at 700°C, shows the dispersion of nano-sized Cu agglomerates on the surface of Mo powders.

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• Fabrication of Porous Mo-Cu by Freeze Drying and Hydrogen Reduction of Metal Oxide Powders
  Hyunji Kang, Ju-Yeon Han, Sung-Tag Oh
  Journal of Korean Powder Metallurgy Institute.2019; 26(1): 1.     CrossRef
• Hydrogen Reduction Behavior and Microstructure Characteristics of Ball-milled CuO-Co₃O₄ Powder Mixtures
  Ju-Yeon Han, Gyuhwi Lee, Hyunji Kang, Sung-Tag Oh
  Journal of Korean Powder Metallurgy Institute.2019; 26(5): 410.     CrossRef

This study is conducted as a preliminary research to verify the feasibility of Ti-based Oxide dispersion strengthened (ODS) alloy. Pure-Ti powder is mixed with Y₂O₃ powder and subsequently, mechanically alloyed at -150°C. The Ti-based ODS powder is hot-isostatically pressed and subsequently hot-rolled for recrystallization. The microstructure consists of elongated grains and Y excess fine particles. The oxide particle size is larger than that of the typical Febased ODS steel. Tensile test shows that the tensile ductility is approximately 25%, while the strength is significantly higher than that of pure Ti. The high-temperature hardness of the Ti-ODS alloy is also significantly higher than that of pure Ti at all temperatures, while being lower than that of Ti-6Al-4V. The dimple structure is well developed, and no evidence of cleavage fracture surface is observed in the fracture surface of the tensile specimen.

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• Spheroidization of Pure-vanadium Powder using Radio Frequency Thermal Plasma Process
  Nana Kwabena Adomako, Seungmin Yang, Min Gyu Lee, N. S. Reddy, Jeoung-Han Kim
  Journal of Korean Powder Metallurgy Institute.2019; 26(4): 305.     CrossRef
• Microstructure and Mechanical Properties of Friction-Welded Alloy 718 and SNCRW Stainless Steel After Post-Weld Heat-Treatment
  Jeoung Han Kim, Nam-Yong Kim, Yu Sik Kong, Nho Kwang Park
  Journal of Welding and Joining.2019; 37(4): 313.     CrossRef

This study investigates the directional recrystallization behavior of Ni based oxide dispersion strengthened (ODS) alloy according to the zone annealing velocity. The zone annealing temperature is set as 1390°C, while the zone velocities are set as 2.5, 4, 6, and 10 cm/h, respectively. The initial microstructure observation of the as-extruded sample shows equiaxed grains of random orientation, with an average grain size of 530 nm. On the other hand, the zone annealed samples show a large deviation in grain size depending on the zone velocities. In particular, grains with a size of several millimeters are observed at 2.5-cm/h zone velocity. It is also found that the preferred orientation varies with the zone annealing velocity. On the basis of these results, this study discusses the role of zone velocities in the directional recrystallization of Ni base ODS alloy.

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• Directional recrystallisation processing: a review
  Chao Yang, Ian Baker
  International Materials Reviews.2021; 66(4): 256.     CrossRef

A unique porous material with controlled pore characteristics can be fabricated by the freeze-drying process, which uses the slurry of organic material as the sublimable vehicle mixed with powders. The essential feature in this process is that during the solidification of the slurry, the dendrites of the organic material should repel the dispersed particles into the interdendritic region. In the present work, a model experiment is attempted using some transparent organic materials mixed with glass powders, which enable in-situ observation. The organic materials used are camphor-naphthalene mixture (hypo- and hypereutectic composition), salol, camphene, and pivalic acid. Among these materials, the constituent phases in camphor-naphthalene system, i.e. naphthalene plate, camphor dendrite, and camphornaphthalene eutectic exclusively repel the glass powders. This result suggests that the control of organic material composition in the binary system is useful for producing a porous body with the required pore structure.

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• Freeze Drying Process and Pore Structure Characteristics of Porous Cu with Various Sublimable Vehicles
  Gyuhwi Lee, Sung-Tag Oh, Myung-Jin Suk, Young-Keun Jeong
  Journal of Korean Powder Metallurgy Institute.2020; 27(3): 198.     CrossRef

Additive manufacturing by electron beam melting is an affordable process for fabricating near net shaped parts of titanium and its alloys. 3D additive-manufactured parts have various kinds of voids, lack of fusion, etc., and they may affect crack initiation and propagation. Post process is necessary to eliminate or minimize these defects. Hot isostatic pressing (HIP) is the main method, which is expensive. The objective of this paper is to achieve an optimum and simple post heat treatment process without the HIP process. Various post heat treatments are conducted for the 3Dprinted Ti-6Al-4V specimen below and above the beta transus temperature (996°C). The as-fabricated EBM Ti-6Al-4V alloy has an α‘-martensite structure and transforms into the α+β duplex phase during the post heat treatment. The fatigue strength of the as-fabricated specimen is 400 MPa. The post heat treatment at 1000°C/30 min/AC increases the fatigue strength to 420 MPa. By post heat treatment, the interior pore size and the pore volume fraction are reduced and this can increase the fatigue limit.

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• Effect of Line Energy Conditions on Mechanical and Fatigue Properties of Ti6Al4V Fabricated by Electron Beam Additive Manufacturing
  Youngsin Choi, Hwi-Jun Kim, Gun-Hee Kim, Chang-Woo Lee, Dong-Geun Lee
  Metals.2021; 11(6): 878.     CrossRef
• Mechanical and Physical Characteristics Analysis of Radius Trauma Plate by EBM Additive Manufacturing
  Kwun-Mook Lim, Sung-Jun Park
  Journal of the Korean Society of Manufacturing Technology Engineers.2020; 29(2): 147.     CrossRef
• Effect of Heat Treatments on Fatigue Properties of Ti-6Al-4V Alloy Fabricated by EBM Additive Manufacturing
  Dong-Geun Lee, Youngsin Choi, P. Villechaise, B. Appolaire, P. Castany, M. Dehmas, C. Delaunay, J. Delfosse, A. Denquin, E. Gautier, L. Germain, N. Gey, T. Gloriant, J.-Y. Hascoët, S. Hémery, Y. Millet, D. Monceau, F. Pettinari-Sturmel, M. Piellard, F. Pr
  MATEC Web of Conferences.2020; 321: 03027.     CrossRef
• Correlation between surface tension and fatigue properties of Ti-6Al-4V alloy fabricated by EBM additive manufacturing
  Youngsin Choi, Dong-Geun Lee
  Applied Surface Science.2019; 481: 741.     CrossRef

Over the last decade, the study of the synthesis of semiconductor colloidal quantum dots has progressed at a tremendous rate. Colloidal quantum dots, which possess unique spectral-luminescent characteristics, are of great interest in the development of novel materials and devices, which are promising for use in various fields. Several studies have been carried out on hot injection synthesis methods. However, these methods have been found to be unsuitable for large-capacity synthesis. Therefore, this review paper introduces synthesis methods other than the hot injection synthesis method, to synthesize quantum dots with excellent optical properties, through continuous synthesis and large capacity synthesis. In addition, examples of the application of synthesized colloid quantum dots in displays, solar cells, and bio industries are provided.