• 한국분말재료학회지
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• 제7권3호
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• pp.143-148
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• 2000

NiAl alloy powders were prepared by mechanical alloying method and bulk specimens were produced using hot isostatic pressing techniques. This study focused on the transformation behavior and properties of Ni-Al mechanically alloyed powders and bulk alloys. Transformation behavior was investigated by differential scanning calorimeter (DSC), XRD and TEM. Particle size distribution and microstructures of mechanically alloyed powders were studied by particle size analyzer and scanning electron microscope (SEM). After 10 hours milling, XRB peak broadening appeared at the alloyed powders with compositions of Ni-36at%Al to 40at%Al. The NiAl and $Ni_3Al$ intermetallic compounds were formed after water quenching of solution treated powders and bulk samples at $1200^{\circ}C$, but the martensite phase was observed after liquid nitrogen quenching of solution treated powders. However, the formation of $Ni_3Al$ intermetallic compounds were not restricted by fast quenching into liquid nitrogen. It is considered to be caused by fast diffusion of atoms for the formation of stable $\beta$(NiAl) phase and $Ni_3Al$ due to nano sized grains during quenching. Amounts of martensite phase increased as the composition of aluminium component decreased in the Ni-Al alloy, which resulted in the increasing damping properties.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.1291-1292
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• 2007

Recently, there were many researches for efficiency improvement of DSC. Among of these works, research of surface treatment is still a prerequisite for electron diffusion, light-harvesting and surface state of DSC.[1] Using of the surface treatment, it can be raise up porosity of $TiO_2$ nano-crystalline structure on photo-electrode. There are chemical, physical, electrical and optical methods which raise up its porosity. In this paper, we have designed and manufactured MOPA-type ultrasonic circuit (100W, frequency and duty variable). Manufactured ultrasonic circuit to use to force cavity density and power into $TiO_2$ paste. Then, we have optimized forcing time, frequency and duty of ultrasonic irradiation for surface treatment of photo-electrode of DSC. In I-V characteristic test of DSC, ultrasonic and thermal treated DSC shows 19% improved its efficiency against monolithic DSC. And it shows stability of light-harvesting from drastically change of light irradiation test.

• 한국재료학회지
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• 제30권5호
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• pp.217-222
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• 2020

The design and fabrication of catalysts with low-cost and high electrocatalytic activity for the oxygen evolution reaction (OER) have remained challenging because of the sluggish kinetics of this reaction. The key to the pursuit of efficient electrocatalysts is to design them with high surface area and more active sites. In this work, we have successfully synthesized a highly stable and active NiCo₂S₄ nanowire array on a Ni-foam substrate (NiCo₂S₄ NW/NF) via a two-step hydrothermal synthesis approach. This NiCo₂S₄ NW/NF exhibits overpotential as low as 275 mV, delivering a current density of 20 mA cm^-2 (versus reversible hydrogen electrode) with a low Tafel slope of 89 mV dec^-1 and superior long-term stability for 20 h in 1 M KOH electrolyte. The outstanding performance is ascribed to the inherent activity of the binder-free deposited, vertically aligned nanowire structure, which provides a large number of electrochemically active surface sites, accelerating electron transfer, and simultaneously enhancing the diffusion of electrolyte.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.127-127
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• 2010

Owing to many advantages on indirect intersubband absorption from the hole miniband to the electron miniband based on the type-II band alignment in InAs/GaSb strained-layer superlattice (SLS), InAs/GaSb SLS infrared photodetector (SLIP) has emerged as a promising system to realize high-detectivity quantum photodetector operating up to room temperature in the spectral range of mid-infrared (MIR) to far-infrared (FIR). In particular, n-barrier-n (n-B-n) structure designed for blocking the majority-carrier dark current makes it possible for MIR/FIR dual-band SLIP whose photoresponse (PR) band can be exclusively selected by the bias polarity. In this study, we present the MIR and FIR photoresponse (PR) mechanism identified by dual-band PR spectra and photoluminescence (PL) profiles taken from InAs/GaSb SLIP. In the MIR/FIR PR spectra measured by changing bias polarity, each spectrum individually shows a series of distinctive peaks related to the transitions from the hole subbands to the conduction one. The PR mechanism at each polarity is discussed in terms of diffusion current, and a superposition of MIR-PR in the FIR-PR spectrum is explained by tunnelling of electrons activated in MIR-SLS. The effective FIR-PR spectrum decomposed into three curves for HH1, LH1, and HH2 has revealed the edge energies of 120, 170, and 220 meV, respectively, and the temperature variation of the MIR-PR edge energies shows that the temperature behavior of the SLS systems can be approximately expressed by the Varshni empirical equation.

• 한국식품영양과학회지
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• 제26권6호
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• pp.1228-1236
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• 1997

Lactobacillus strains were isolated from volunteer's feces, including from newly-born infants and adults in their 20's, by using differential MRS-BPB plates. Total 56 presumptive Lactobacillus strains were isolated and the bacteriocin productions by the isolates were examined by agar diffusion method. Six bacteriocin-producing strains were confirmed. Among them, two isolates, HU-1 and H22-3, showed the most outstanding antimicrobial activities, which were not affected by pH adjustments or catalase treatments of culture. HU-1 was originated from a two-years old boy and H22-3 was originated from a newly-born infant. HU-1 and H22-3 had the same morphology(short rod) when examined by scanning electron microscope, and the same biochemical traits including growth temperature range, salt tolerance and sugar-fermenting abilities. But the growth-inhibition spectrum and plasmid profiles of HU-1 and H22-3 were different. Both strains inhibited the growth of various Gram (+) microorganisms including Listeria monocytogenes. Micrococcus luteus, and Staphylococcus aureus in addition to many species of lactic acid bacteria, indicating the production of broad-spectrum bacteriocins. Bacteriocins produced by HU-1 and H22-3 were stable up to 90℃, 15 min heat treatments. Their activities were not affected by pepsin or trypsin treatments but destroyed by proteinaseK or pronase treatments.

• 대한금속재료학회지
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• 제48권9호
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• pp.856-860
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• 2010

Silver nanoparticles were formed on silica substrates through thin film dewetting at high temperature. The microstructural and morphological evolution of the particles were characterized as a function of processing variables such as initial film thickness, annealing time, and temperature. Silver thin films were deposited onto the silica using a pulsed laser deposition system and annealed in reducing atmosphere to induce agglomeration of the films. The film thicknesses before dewetting were in the range of 5 to 25 nm. A noticeable agglomeration occurs with annealing at temperatures higher than $300^{\circ}C$, and higher annealing temperature increases particle size uniformity for the same film thickness sample. Average particle size linearly correlates to the film thickness, but it does not strongly depend on annealing temperature and time, although threshold temperature for complete dewetting increases with an increase of film thickness. Lower annealing temperature develops faceted surface morphology of the silver particles by enhancing the growth of the low index crystal plane of the particles.

• 대한금속재료학회지
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• 제49권12호
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• pp.950-955
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• 2011

In the present study, the formation of hollow Cu oxide nanoparticles through the oxidation process at temperatures from 200 to $300^{\circ}C$ has been studied by transmission electron microscopy with Cu nanoparticles produced by the plasma arc discharge method. The Cu nanoparticles had a thin oxide layer on the surface at room temperature and the thickness of this oxide layer increased during oxidation in atmosphere at $200-300^{\circ}C$ However, the oxide layer consisted of $Cu_2O$ and CuO after oxidation at $200^{\circ}C$ whereas this layer was comprised of only CuO after oxidation at $300^{\circ}C$ On the other hand, hollow Cu oxide nanoparticles are obtained as a result of vacancy aggregation in the oxidation processes, resulting from the rapid outward diffusion of metal ions through the oxide layer during the oxidation process.

• 대한금속재료학회지
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• 제50권9호
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• pp.653-657
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• 2012

In this study, a molybdenum disilicide ($MoSi_2$) coating process was investigated by hydrogen reduction and Si-pack cementation. At first, the metallic Mo coating was carried out by hydrogen reduction of $MoO_3$ powder at $750^{\circ}C$ for various holding times (1, 2, 3 h) in hydrogen atmosphere. A $4.3{\mu}m$ thick metallic molybdenum thin film was formed at 3 h. $MoSi_2$ was obtained by Si-pack cementation on molybdenum thin film through hydrogen reduction processing. It was carried out using $Si:Al_2O_3:NH_4Cl=5:92:3$ (wt%) packs at $900^{\circ}C$ for various holding times (30, 60, 90 min) in Ar atmosphere. When the holding time was 90 min, a $MoSi_2$ layer was coated successfully and a $15.4{\mu}m$ thickness was observed.

• Advances in nano research
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• 제5권4호
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• pp.373-392
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• 2017

Silver nanoparticles (AgNPs) were successfully synthesized through a simple green route using the Nelumbo nucifera leaf, stem and flower extracts. These nanoparticles showed characteristic UV-Vis absorption peaks between 410-450 nm which arises due to the plasmon resonance of silver nanoparticles. The Fourier transform infrared spectroscopy (FT-IR) confirmed the presence of amides and which acted as the stabilizing agent. X-ray diffraction spectrum of the nanoparticles confirmed the Face centered cubic (FCC) structure of the formed AgNPs. Dynamic light scattering technique was used to measure hydrodynamic diameter (68.6 nm to 88.1 nm) and zeta potential (-55.4 mV, -57.9 mV and 98.9 mV) of prepared AgNPs. The scanning electron micrographs of dislodged nanoparticles in aqueous solution showed the production of reasonably monodispersed silver nanoparticles (1-100 nm). The antimicrobial activity of prepared AgNPs was evaluated against fungi, Gram-positive and Gram-negative bacteria using disc diffusion method. Anti-corrosion studies were carried out using coupon method (mild steel and iron) and dye degradation studies were carried out by assessing photo-catalytic activity of Nelumbo nucifera extracts mediated AgNPs.

• Bulletin of the Korean Chemical Society
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• 제17권2호
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• pp.162-167
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• 1996

Two redox processes of methyl viologen (+2/+, +/0) in acetonitrile were investigated by using channel electrode voltammetric and in situ electrochemical ESR methods. Two separated unequal plateau currents of the first (+2/+) and second (+/0) redox processes of the viologen were observed in the channel electrode voltammograms and showed a cube-root depedndence on the electrolyte flow rate, respectively. The simple Levich analysis resulted in two different diffusion coefficients of $D_{+2}=2.2{\times}10^{-5}\;cm^2/s$ and $D_+=3.0{\times}10^{-5}cm^2/s$ from the limiting currents. In situ electrochemical ESR studies were performed for the monocation radicals generated at the potentials of the two plateau currents in the electrolyte flow range $1.3{\times}10^{-1}{\geq}v_f{\geq}2.7{\times}10^{-3}\;cm^3/s$. Backward implicitfinite difference method was employed to simulate the electrochemical kinetic problem of two sequential electron transfers ($MV^{+2}+e{\leftrightarrows}MV^+,\;MV^{+}+e{\leftrightarrows}MV^0$) coupled with reversible comproportionation ($MV^{2+}+MV^0{{\leftrightarrows}^{k_f}_{k_b}}2MV^+$). $k_f$ was found to be greater than ($10^6M^{-1}s^{-1}.