High-quality colloidal CdSe/ZnS (core/shell) is synthesized using a continuous microreactor. The particle size of the synthesized quantum dots (QDs) is a function of the precursor flow rate; as the precursor flow rate increases, the size of the QDs decreases and the band gap energy increases. The photoluminescence properties are found to depend strongly on the flow rate of the CdSe precursor owing to the change in the core size. In addition, a gradual shift in the maximum luminescent wave (λ_max) to shorter wavelengths (blue shift) is found owing to the decrease in the QD size in accordance with the quantum confinement effect. The ZnS shell decreases the surface defect concentration of CdSe. It also lowers the thermal energy dissipation by increasing the concentration of recombination. Thus, a relatively high emission and quantum yield occur because of an increase in the optical energy emitted at equal concentration. In addition, the maximum quantum yield is derived for process conditions of 0.35 ml/min and is related to the optimum thickness of the shell material.

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• Quantum materials made in microfluidics - critical review and perspective
  M. Wojnicki, V. Hessel
  Chemical Engineering Journal.2022; 438: 135616.     CrossRef
• Poly(methylmethacrylate) coating on quantum dot surfaces via photo-chemical reaction for defect passivation
  Doyeon Kim, So-Yeong Joo, Chan Gi Lee, Bum-Sung Kim, Woo-Byoung Kim
  Journal of Photochemistry and Photobiology A: Chemistry.2019; 376: 206.     CrossRef
• Multimodal luminescence properties of surface-treated ZnSe quantum dots by Eu
  Ji Young Park, Da-Woon Jeong, Kyoung-Mook Lim, Yong-Ho Choa, Woo-Byoung Kim, Bum Sung Kim
  Applied Surface Science.2017; 415: 8.     CrossRef

Carbon nanofiber (CNF) composites coated with spindle-shaped Fe₂O₃ nanoparticles (NPs) are fabricated by a combination of an electrospinning method and a hydrothermal method, and their morphological, structural, and chemical properties are measured by field-emission scanning electron microscopy, transmission electron microscopy, Xray diffraction, and X-ray photoelectron spectroscopy. For comparison, CNFs and spindle-shaped Fe₂O₃ NPs are prepared by either an electrospinning method or a hydrothermal method, respectively. Dye-sensitized solar cells (DSSCs) fabricated with the composites exhibit enhanced open circuit voltage (0.70 V), short-circuit current density (12.82 mA/cm2), fill factor (61.30%), and power conversion efficiency (5.52%) compared to those of the CNFs (0.66 V, 11.61 mA/cm2, 51.96%, and 3.97%) and spindle-shaped Fe₂O₃ NPs (0.67 V, 11.45 mA/cm2, 50.17%, and 3.86%). This performance improvement can be attributed to a synergistic effect of a superb catalytic reaction of spindle-shaped Fe₂O₃ NPs and efficient charge transfer relative to the one-dimensional nanostructure of the CNFs. Therefore, spindle-shaped Fe₂O₃-NPcoated CNF composites may be proposed as a potential alternative material for low-cost counter electrodes in DSSCs.

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• Ni Nanoparticles-Graphitic Carbon Nanofiber Composites for Pt-Free Counter Electrode in Dye-Sensitized Solar Cells
  Dong-Hyeun Oh, Bon-Ryul Koo, Yu-Jin Lee, HyeLan An, Hyo-Jin Ahn
  Korean Journal of Materials Research.2016; 26(11): 649.     CrossRef

We demonstrate the electrochromic properties of TiO₂ nanotubes prepared by an anodization process and investigate the effects of heat treatment and viologen incorporation on them. The morphology and crystal structure of anodized TiO₂ nanotubes are investigated by scanning electron microscopy and X-ray diffraction. As-formed TiO₂ nanotubes have straight tubular layers with an amorphous structure. As the annealing temperature increases, the anodized TiO₂ nanotubes are converted to the anatase and rutile phases with some cracks on the tube surface and irregular morphology. Electrochemical results reveal that amorphous TiO₂ nanotubes annealed at 150°C have the largest oxidation/ reduction current, which leads to the best electrochromic performance during the coloring/bleaching process. Viologenanchored TiO₂ nanotubes show superior electrochromic properties compared to pristine TiO₂ nanotubes, which indicates that the incorporation of a viologen can be an effective way to enhance the electrochromic properties of TiO₂ nanotubes.

Y₂O₃–H₃BO₃:Eu³⁺ powders are synthesized using a mechanical alloying method, and their photoluminescence (PL) properties are investigated through luminescence spectrophotometry. For samples milled for 300 min, some Y₂O₃ peaks ([222], [440], and [622]) and amorphous formations are observed. The 300-min-milled mixture annealed at 800°C for 1 h with Eu = 8 mol% has the strongest PL intensity at every temperature increase of 100°C (increasing from 700 to 1200°C in 100°C increments). PL peaks of the powder mixture, as excited by a xenon discharge lamp (20 kW) at 240 nm, are detected at approximately 592 nm (orange light, ⁵D_o → ⁷F₁), 613 nm, 628 nm (red light, ⁵D_o → ⁷F₁), and 650 nm. The PL intensity of powder mixtures milled for 120 min is generally lower than that of powder mixtures milled for 300 min under the same conditions. PL peaks due to YBO3 and Y₂O₃ are observed for 300-min-milled Y₂O₃–H₃BO₃ with Eu = 8 mol% after annealing at 800°C for 1 h.

A powder injection molding process is developed and optimized for piezoelectric PAN-PZT ceramics. Torque rheometer experiments are conducted to determine the optimal solids loading, and the rheological property of the feedstock is evaluated using a capillary rheometer. Appropriate debinding conditions are chosen using a thermal gravity analyzer, and the debound specimens are sintered using sintering conditions determined in a preliminary investigation. Piezoelectric performance measures, including the piezoelectric charge constant and dielectric constant, are measured to verify the developed process. The average values of the measured piezoelectric charge constant and dielectric constant are 455 pC/N and 1904, respectively. Powder injection molded piezoelectric ceramics produced by the optimized process show adequate piezoelectric performance compared to press-sintered piezoelectric ceramics.

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• Study on Rheological Behavior and Mechanical Properties of PMN–PZT Ceramic Feedstock
  Jae Man Park, Jun Sae Han, Joo Won Oh, Seong Jin Park
  Metals and Materials International.2021; 27(5): 1069.     CrossRef
• Investigation of stainless steel 316L/zirconia joint part fabricated by powder injection molding
  Chang Woo Gal, Sang Soo Han, Jun Sae Han, Dongguo Lin, Seong Jin Park
  International Journal of Applied Ceramic Technology.2019; 16(1): 315.     CrossRef
• Fabrication of pressureless sintered Si3N4 ceramic balls by powder injection molding
  Chang Woo Gal, Gi Woung Song, Woon Hyung Baek, Hyung Kyu Kim, Dae Keun Lee, Ki Wook Lim, Seong Jin Park
  Ceramics International.2019; 45(5): 6418.     CrossRef
• Experimental analysis for fabrication of high-aspect-ratio piezoelectric ceramic structure by micro-powder injection molding process
  Jun Sae Han, Chang Woo Gal, Jae Man Park, Jong Hyun Kim, Seong Jin Park
  Materials Research Express.2018; 5(4): 046303.     CrossRef

P-type ternary Bi_0.5Sb_1.5Te₃ alloys are fabricated via mechanical alloying (MA) and spark plasma sintering (SPS). Different ball sizes are used in the MA process, and their effect on the microstructure; hardness, and thermoelectric properties of the p-type BiSbTe alloys are investigated. The phases of milled powders and bulks are identified using an X-ray diffraction technique. The morphology of milled powders and fracture surface of compacted samples are examined using scanning electron microscopy. The morphology, phase, and grain structures of the samples are not altered by the use of different ball sizes in the MA process. Measurements of the thermoelectric (TE) transport properties including the electrical conductivity, Seebeck coefficient, and power factor are measured at temperatures of 300- 400 K for samples treated by SPS. The TE properties do not depend on the ball size used in the MA process.

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• Investigation of Spark Plasma Sintering Temperature on Microstructure and Thermoelectric Properties of p-type Bi-Sb-Te alloys
  Jin-Koo Han, Dong-won Shin, Babu Madavali, Soon-Jik Hong
  Journal of Korean Powder Metallurgy Institute.2017; 24(2): 115.     CrossRef
• Flexible Thermoelectric Device Using Thick Films for Energy Harvesting from the Human Body
  Han Ki Cho, Da Hye Kim, Hye Sun Sin, Churl-Hee Cho, Seungwoo Han
  Journal of the Korean Ceramic Society.2017; 54(6): 518.     CrossRef
• Investigation of the Microstructure and Thermoelectric Properties of P-Type BiSbTe Alloys by Usage of Different Revolutions Per Minute (RPM) During Mechanical Milling
  S.-M. Yoon, B. Madavali, Y.-N. Yoon, S.-J. Hong
  Archives of Metallurgy and Materials.2017; 62(2): 1167.     CrossRef
• Mechanical and thermoelectric properties of Bi2−xSbxTe3 prepared by using encapsulated melting and hot pressing
  Woo-Jin Jung, Il-Ho Kim
  Journal of the Korean Physical Society.2016; 69(8): 1328.     CrossRef

The recent rise in applications of thermoelectric materials has attracted interest in studies toward the fabrication of thermoelectric materials using mass production techniques. In this study, we successfully fabricate n-type Bi₂Te_2.7Se_0.3 material by a combination of mass production powder metallurgy techniques, gas atomization, and spark plasma sintering. In addition, to examine the effects of hydrogen reduction in the microstructure, the thermoelectric and mechanical properties are measured and analyzed. Here, almost 60% of the oxygen content of the powder are eliminated after hydrogen reduction for 4 h at 360°C. Micrographs of the powder show that the reduced powder had a comparatively clean surface and larger grain sizes than unreduced powder. The density of the consolidated bulk using as-atomized powder and reduced atomized powder exceeds 99%. The thermoelectric power factor of the sample prepared by reduction of powder is 20% better than that of the sample prepared using unreduced powder.

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• Enhancing thermoelectric performance of K-doped polycrystalline SnSe through band engineering tuning and hydrogen reduction
  Nan Xin, Yifei Li, Guihua Tang, Longyun Shen
  Journal of Alloys and Compounds.2022; 899: 163358.     CrossRef
• The effect of powder pre-treatment on the mechanical and thermoelectric properties of spark plasma sintered N-type bismuth telluride
  Ahmed A. Abdelnabi, Vickram Lakhian, Joseph R. McDermid, James S. Cotton
  Journal of Alloys and Compounds.2021; 874: 159782.     CrossRef
• Investigation of Spark Plasma Sintering Temperature on Microstructure and Thermoelectric Properties of p-type Bi-Sb-Te alloys
  Jin-Koo Han, Dong-won Shin, Babu Madavali, Soon-Jik Hong
  Journal of Korean Powder Metallurgy Institute.2017; 24(2): 115.     CrossRef
• The Preparation and Growth Mechanism of the Recovered Bi2Te3 Particles with Respect to Surfactants
  Hyeongsub So, Eunpil Song, Yong-Ho Choa, Kun-Jae Lee
  Journal of Korean Powder Metallurgy Institute.2017; 24(2): 141.     CrossRef
• Enhanced thermoelectric cooling properties of Bi2Te3−xSex alloys fabricated by combining casting, milling and spark plasma sintering
  Seung Tek Han, Pradip Rimal, Chul Hee Lee, Hyo-Seob Kim, Yongho Sohn, Soon-Jik Hong
  Intermetallics.2016; 78: 42.     CrossRef

This study investigates the influence of sintering temperature on the magnetic properties and frequency dispersion of the complex permeability of Ni–Zn–Cu ferrites used for magnetic shielding in near-field communication (NFC) systems. Sintered specimens of (Ni_0.7Zn_0.3)_0.96Cu_0.04Fe₂O₄ are prepared by conventional ceramic processing. The complex permeability is measured by an RF impedance analyzer in the range of 1 MHz to 1.8 GHz. The real and imaginary parts of the complex permeability depend sensitively on the sintering temperature, which is closely related to the microstructure, including grain size and pore distribution. In particular, internal pores within grains produced by rapid grain growth decrease the permeability and increase the magnetic loss at the operating frequency of NFC (13.56 MHz). At the optimized sintering temperature (1225-1250°C), the highest permeability and lowest magnetic loss can be obtained.

As precursors of cathode materials for lithium ion batteries, Ni_1/3Co_1/3Mn_1/3(OH)₂ powders are prepared in a continuously stirred tank reactor via a co-precipitation reaction between aqueous metal sulfates and NaOH in the presence of NH4OH in air or nitrogen ambient. Calcination of the precursors with Li₂CO₃ for 8 h at 1,000°C in air produces dense spherical cathode materials. The precursors and final powders are characterized by X-ray diffraction (XRD), scanning electron microscopy, particle size analysis, tap density measurement, and thermal gravimetric analysis. The precursor powders obtained in air or nitrogen ambient show XRD patterns identified as Ni_1/3Co_1/3Mn_1/3(OH)₂. Regardless of the atmosphere, the final powders exhibit the XRD patterns of LiNi_1/3Co_1/3Mn_1/3O₂ (NCM). The precursor powders obtained in air have larger particle size and lower tap density than those obtained in nitrogen ambient. NCM powders show similar tendencies in terms of particle size and tap density. Electrochemical characterization is performed after fabricating a coin cell using NCM as the cathode and Li metal as the anode. The NCM powders from the precursors obtained in air and those from the precursors obtained in nitrogen have similar initial charge/discharge capacities and cycle life. In conclusion, the powders co-precipitated in air can be utilized as precursor materials, replacing those synthesized in the presence of nitrogen injection, which is the usual industrial practice.

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• Stabilization of High Nickel Cathode Materials with Core-Shell Structure via Co-precipitation Method
  Minjeong Kim, Soonhyun Hong, Heongkwon Jeon, Jahun Koo, Heesang Lee, Gyuseok Choi, Chunjoong Kim
  Korean Journal of Materials Research.2022; 32(4): 216.     CrossRef
• Spherical agglomeration of nickel-manganese-cobalt hydroxide in turbulent Batchelor vortex flow
  Xiaotong Sun, Jinsoo Kim, Woo-Sik Kim
  Chemical Engineering Journal.2021; 421: 129924.     CrossRef
• Design strategies for development of nickel-rich ternary lithium-ion battery
  Kyu Hwan Choi, Xuyan Liu, Xiaohong Ding, Qiang Li
  Ionics.2020; 26(3): 1063.     CrossRef
• Effect of Single and Dual Doping of Rare Earth Metal Ce and Nd Elements on Electrochemical Properties of LiNi_0.83 Co_0.11Mn_0.06O₂ Cathode Lithium-ion Battery Material
  Yoo-Young Kim, Jong-Keun Ha, Kwon-Koo Cho
  Journal of Korean Powder Metallurgy Institute.2019; 26(1): 49.     CrossRef
• Effects of Precursor Co-Precipitation Temperature on the Properties of LiNi1/3Co1/3Mn1/3O2 Powders
  Woonghee Choi, Chan Hyoung Kang
  Journal of Korean Powder Metallurgy Institute.2016; 23(4): 287.     CrossRef

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.

Additive manufacturing (AM) is defined as the manufacture of three-dimensional tangible products by additively consolidating two-dimensional patterns layer by layer. In this review, we introduce four fundamental conceptual pillars that support AM technology: the bottom-up manufacturing factor, computer-aided manufacturing factor, distributed manufacturing factor, and eliminated manufacturing factor. All the conceptual factors work together; however, business strategy and technology optimization will vary according to the main factor that we emphasize. In parallel to the manufacturing paradigm shift toward mass personalization, manufacturing industrial ecology evolves to achieve competitiveness in economics of scope. AM technology is indeed a potent candidate manufacturing technology for satisfying volatile and customized markets. From the viewpoint of the innovation technology adoption cycle, various pros and cons of AM technology themselves prove that it is an innovative technology, in particular a disruptive innovation in manufacturing technology, as powder technology was when ingot metallurgy was dominant. Chasms related to the AM technology adoption cycle and efforts to cross the chasms are considered.

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• SiC-Si composite part fabrication via SiC powder binder jetting additive manufacturing and molten-Si infiltration
  Ji-Won Oh, Jinsu Park, Sahn Nahm, Hanshin Choi
  International Journal of Refractory Metals and Hard Materials.2021; 101: 105686.     CrossRef
• Recent Trends and Application Status of the Metal Matrix Composites (MMCs)
  Hyo-Seop Kim
  Journal of Korean Powder Metallurgy Institute.2020; 27(2): 164.     CrossRef
• Metal Additive Manufacturing Cycle in Aerospace Industry: A Comprehensive Review
  B. Barroqueiro, A. Andrade-Campos, R. A. F. Valente, V. Neto
  Journal of Manufacturing and Materials Processing.2019; 3(3): 52.     CrossRef
• Technology Trend of the additive Manufacturing (AM)
  Ji-Won Oh, Hyunwoong Na, Hanshin Choi
  Journal of Korean Powder Metallurgy Institute.2017; 24(6): 494.     CrossRef

Lithium-ion batteries (LIBs) are rapidly improving in capacity and life cycle characteristics to meet the requirements of a wide range of applications, such as portable electronics, electric vehicles, and micro- or nanoelectromechanical systems. Recently, atomic layer deposition (ALD), one of the vapor deposition methods, has been explored to expand the capability of LIBs by producing near-atomically flat and uniform coatings on the shell of nanostructured electrodes and membranes for conventional LIBs. In this paper, we introduce various ALD coatings on the anode, cathode, and separator materials to protect them and improve their electrochemical and thermomechanical stability. In addition, we discuss the effects of ALD coatings on the three-dimensional structuring and conduction layer through activation of electrochemical reactions and facilitation of fluent charge collection.

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• Atomic Layer Deposition for Powder Coating
  Seok Choi, Jeong Hwan Han, Byung Joon Choi
  Journal of Korean Powder Metallurgy Institute.2019; 26(3): 243.     CrossRef
• Formation of Uniform SnO2 Coating Layer on Carbon Nanofiber by Pretreatment in Atomic Layer Deposition
  Dong Ha Kim, Doh-Hyung Riu, Byung Joon Choi
  journal of Korean Powder Metallurgy Institute.2018; 25(1): 43.     CrossRef