• 대한금속재료학회지
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• 제50권1호
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• pp.1-7
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• 2012

The fracture resistance and tensile properties of $Y_2O_3$ oxide dispersion strengthened steel containing 9 wt% Cr(9Cr-ODS) were measured at various temperatures up to $700^{\circ}C$. The fracture characteristics were compared with those of commercial E911 ferritic/martensitic steel. The strength of 9Cr-ODS was at least 30% higher than that of E911 steel at the test temperatures below $500^{\circ}C$. The strength difference between the two materials was almost diminished at $700^{\circ}C$. 9Cr-ODS showed cleavage fracture behavior at room temperature and unstable crack growth behaviors at $300^{\circ}C$ and $500^{\circ}C$. The J-R fracture resistance of 9Cr-ODS was much lower than that of E911 steel at all temperatures. It was deduced that the coarse $Cr_2O_3$ particles that were formed during the alloying process provided the crack initiation sites of cleavage fracture in 9Cr-ODS.

• 대한환경공학회지
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• 제32권6호
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• pp.547-554
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• 2010

본 연구에서는 나노구조의 새로운 망간산화물 입자(즉, 블랙-버네사이트)를 합성하여 물질특성 및 1,4-naphthoquinone (1,4-NPQ)을 대상으로 반응매개체 존재 하에서의 산화-변환반응 효율을 조사하였고, 그 결과를 기존의 McKenzie 방법으로 얻은 망간산화물(즉, 브라운-버네사이트)의 결과와 비교 분석하였다. XRD 분석 결과 합성한 망간산화물 입자의 결정상은 버네사이트(${\delta}-MnO_2$)임을 확인하였으며, SEM 측정결과 입자표면은 섬유상의 구조에 의한 나노크기의 미세기공을 가진 볼모양(ball-like)의 형태를 보였다. 배치실험 결과, 나노구조의 망간산화물에 의한 1,4-NPQ 제거는 유사-1차 반응을 따랐으며 기존 망간산화물과 비교해 BET 비표면적 값이 작음(41.05 vs 19.80 $m^2/g$)에도 불구하고 약 2.3배의 높은 속도 상수값을 보였다. 이러한 결과는 블랙-버네사이트에서의 상대적으로 높은 결정성과 나노구조의 표면 특성에 기인한 것으로 해석되며, 블랙-버네사이트 입자가 퀴논화합물에 대하여 상대적으로 높은 반응성을 보임을 알 수 있다. 반응산물에 대한 HPLC 크로마토그램 분석 결과로부터 블랙 버네사이트 입자에 의한 1,4-NPQ의 제거는 반응 매개체인 catechol 존재 하에서의 상호-결합반응을 통한 중합체 생성을 통해 제거됨을 확인하였다.

• Restorative Dentistry and Endodontics
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• 제47권4호
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• pp.38.1-38.15
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• 2022

Objectives: This study investigated the cytotoxicity, radiopacity, pH, and dentinal tubule penetration of a paste of 1.0% calcium-doped zinc oxide nanocrystals (ZnO:1.0Ca) combined with propylene glycol (PRG) or polyethylene glycol and propylene glycol (PEG-PRG). Materials and Methods: The pastes were prepared by mixing calcium hydroxide [Ca(OH)₂] or ZnO:1.0Ca with PRG or a PEG-PRG mixture. The pH was evaluated after 24 and 96 hours of storage in deionized water. Digital radiographs were acquired for radiopacity analysis and bubble counting of each material. The materials were labeled with 0.1% fluorescein and applied to root canals, and images of their dentinal tubule penetration were obtained using confocal laser scanning microscopy. RAW264.7 macrophages were placed in different dilutions of culture media previously exposed to the materials for 24 and 96 hours and tested for cell viability using the MTT assay. Analysis of variance and the Tukey test (α = 0.05) were performed. Results: ZnO:1.0Ca materials showed lower viability at 1:1 and 1:2 dilutions than Ca(OH)₂ materials (p < 0.0001). Ca(OH)₂ had higher pH values than ZnO:1.0Ca at 24 and 96 hours, regardless of the vehicle (p < 0.05). ZnO:1.0Ca pastes showed higher radiopacity than Ca(OH)₂ pastes (p < 0.01). No between-material differences were found in bubble counting (p = 0.0902). The ZnO:1.0Ca pastes had a greater penetration depth than Ca(OH)₂ in the apical third (p < 0.0001). Conclusions: ZnO:1.0Ca medicaments presented higher penetrability, cell viability, and radiopacity than Ca(OH)₂. Higher values of cell viability and pH were present in Ca(OH)₂ than in ZnO:1.0Ca.

• Bulletin of the Korean Chemical Society
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• 제26권11호
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• pp.1653-1668
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• 2005

Assembly of hybrid mesophases through the combination of amphiphilic block copolymers, acting as structuredirecting agents, and silicon sources using low acid catalyst concentration regimes is a versatile strategy to produce large quantities of high-quality ordered large-pore mesoporous silicas in a very reproducible manner. Controlling structural and textural properties is proven to be straightforward at low HCl concentrations with the adjustment of synthesis gel composition and the option of adding co-structure-directing molecules. In this account, we illustrate how various types of large-pore mesoporous silica can easily be prepared in high phase purity with tailored pore dimensions and tailored level of framework interconnectivity. Silica mesophases with two-dimensional hexagonal (p6mm) and three-dimensional cubi (Fm$\overline{3}$m, Im$\overline{3}$m and Ia$\overline{3}$d) symmetries are generated in aqueous solution by employing HCl concentrations in the range of 0.1−0.5 M and polyalkylene oxide-based triblock copolymers such as Pluronic P123 $(EO_{20}-PO_{70}-EO_{20})$ and Pluronic F127 $(EO_{106}-PO_{70}-EO_{106})$. Characterizations by powder X-ray diffraction, nitrogen physisorption, and transmission electron microscopy show that the mesoporous materials all possess high specific surface areas, high pore volumes and readily tunable pore diameters in narrow distribution of sizes ranging from 4 to 12 nm. Furthermore, we discuss our recent advances achieved in order to extend widely the phase domains in which single mesostructures are formed. Emphasis is put on the first synthetic product phase diagrams obtained in $SiO_2$-triblock copolymer-BuOH-$H_2O$ systems, with tuning amounts of butanol and silica source correspondingly. It is expected that the extended phase domains will allow designed synthesis of mesoporous silicas with targeted characteristics, offering vast prospects for future applications.

• 한국세라믹학회지
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• 제53권4호
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• pp.400-405
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• 2016

Ferric oxide (${\alpha}-Fe_2O_3$, hematite) is an n-type semiconductor; due to its narrow band gap ($E_g=2.1eV$), it is a highly attractive and desirable material for use in solar hydrogenation by water oxidation. However, the actual conversion efficiency achieved with $Fe_2O_3$ is considerably lower than the theoretical values because the considerably short diffusion length (2-4 nm) of holes in $Fe_2O_3$ induces excessive charge recombination and low absorption. This is a significant hurdle that must be overcome in order to obtain high solar-to-hydrogen conversion efficiency. In consideration of this, it is thought that elemental doping, which may make it possible to enhance the charge transfer at the interface, will have a marked effect in terms of improving the photoactivities of ${\alpha}-Fe_2O_3$ photoanodes. Herein, we report on the synthesis by pulsed electrodeposition of ${\alpha}-Fe_2O_3$-based anodes; we also report on the resulting photoelectrochemical (PEC) properties. We attempted Ti-doping to enhance the PEC properties of ${\alpha}-Fe_2O_3$ anodes. It is revealed that the photocurrent density of a bare ${\alpha}-Fe_2O_3$ anode can be dramatically changed by controlling the condition of the electrodeposition and the concentration of $TiCl_3$. Under optimum conditions, a modified ${\alpha}-Fe_2O_3$ anode exhibits a maximum photocurrent density of $0.4mA/cm^2$ at 1.23 V vs. reversible hydrogen electrode (RHE) under 1.5 G simulated sunlight illumination; this photocurrent density value is about 3 times greater than that of unmodified ${\alpha}-Fe_2O_3$ anodes.

• 한국수소및신에너지학회논문집
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• 제21권4호
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• pp.271-277
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• 2010

$(Ba(Zr_{0.85}Y_{0.15})O_{3-\delta})$ oxide, showing high protonic conductivity at high temperatures and good chemical stability with $CO_2$ are referred to as hydrogen separation membrane. For high efficiency of hydrogen separation ($H_2$ flux and selectivity) and low fabrication cost, ultimate thin and dense BZY-Ni layer has to be coated on a porous substrate such as $ZrO_2$. Aerosol depostion (AD) process is a novel technique to grow ceramic film with high density and nano-crystal structure at room-temperature, and may be applicable to the fabrication process of AD integration ceramic layer effectively. XRD, SEM, X-ray mapping measurements were conducted in order to analyze the characteristics of BZY-Ni membrane fabricated by AD process. it is observed that it is homogeneous distribution for BZY-Ni. The result of $H_2$ permeation rate suggests that BZY-Ni composite is higher than BZY.

• Journal of Electrochemical Science and Technology
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• 제11권3호
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• pp.273-281
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• 2020

Constructing and making highly active and stable nanostructured Pt-based catalysts with ultralow Pt loading are still electrifying for electrochemical applications such as water electrolysis and fuel cells. In this study, MoO₃ ribbons (RBs) of few micrometer in length is successfully synthesized via hydrothermal synthesis. Subsequently, 3-dimentional (3D)-silicate layer for about 10 to 15 nm is introduced via chemical deposition onto the pre-formed MoO₃ RBs; to setup the platform for Pt metaldots (MDs) deposition. In comparison with the bare MoO₃ RBs, the MoO₃-Si has served as a efficient solid-support for stabilizing and accommodating the uniform deposition of sub-2 nm Pt MDs. Such a structural design would effectively assist in improving the electronic conductivity of a fabricated MoO₃-Si-Pt catalyst towards MOR; the interfaced, porous and 3D silicate layer has assisted in an efficient mass transport and quenching the poisonous CO_ads species leading to a significant electrocatalytic performance for MOR in alkaline medium. Uniformly decorated, sub-2 nm sized Pt MDs has synergistically oxidized the MeOH in association with the MoO₃-Si solid-support hence, synergistic catalytic activity has been achieved. Present facile approach can be extended for fabricating variety of highly efficient Metal Oxide-Metal Nanocomposite for energy harvesting applications.

• Journal of Electrochemical Science and Technology
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• 제9권3호
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• pp.202-211
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• 2018

In this work, Fe-Pd alloy films have been electrodeposited on different substrates using an electrolyte containing $[Pd(NH_3)_4]^{2+}$ (0.02 M) and $[Fe-Citrate]^{2+}$ (0.2 M). The influences of substrate and overpotential on chemical composition, nucleation and growth kinetics as well as the electrodeposited films morphology have been investigated using energy dispersive X-ray spectroscopy (EDS), current-time transients, scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) patterns. In all substrates - brass, copper and sputtered fluorine doped tin oxide on glass (FTO/glass) - Fe content of the electrodeposited alloys increases by increasing the overpotential. Also the cathodic current efficiency is low due to high rate of $H_2$ co-reduction. Regarding the chronoamperometry current-time transients, it has been demonstrated that the nucleation mechanism is instantaneous with a typical three dimensional (3D) diffusion-controlled growth in the case of brass and copper substrates; while for FTO, the growth mode changes to 3D progressive. At a constant overpotential, the calculated number of active nucleation sites for metallic substrates is much higher than that of FTO/glass; however by increasing the overpotential, the number of active nucleation sites increases. The SEM micrographs as well as the XRD patterns reveal the formation of Fe-Pd alloy thin films with nanostructure arrangement and ultra-fine grains.

• 공업화학
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• 제20권6호
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• pp.586-592
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• 2009

나노 크기의 배향성을 갖는 구조물의 제작은 자연에 존재하는 여러 가지 형상의 모방을 가능하게 한다. 고분자는 가격이 매우 저렴하며 합성과 가공 그리고 그 구조가 잘 알려져 있는 장점을 갖고 있어 필름(film)의 표면에 이러한 나노 구조물을 제작하고 나노 구조의 특성을 발현하는데 손쉽게 활용할 수 있는 재료이다. 나노 구조물을 제작하는 방법 중 양극산화를 통하여 제작한 다공성 알루미나 템플레이트(porous alumina template)는 매우 규칙적으로 정렬되어 있고 제어하는 공정이 비교적 쉽고 경제적이기 때문에 이를 이용한 연구가 매우 활발하게 진행되고 있다. 본 총설에서는 양극산화 알루미나 템플레이트의 제작과 이를 이용한 나노 구조 고분자 필름의 제작을 설명하고 이러한 나노 구조 필름의 응용범위 및 응용에 필요한 특성에 대하여 기술하였다.

• 대한금속재료학회지
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• 제50권8호
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• pp.605-611
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• 2012

ZnO nanostructures were grown on R-plane sapphire substrates with seed layers annealed at different temperatures ranging from 600 to $800^{\circ}C$. The properties of the ZnO nanostructures were investigated by scanning electron microscopy, high-resolution X-ray diffraction, UV-visible spectrophotometer, and photoluminescence. For the as-prepared seed layers, ZnO nanorods and ZnO nanosheets were observed. However, only ZnO nanorods were grown when the annealing temperature was above $700^{\circ}C$. The crystal qualities of the ZnO nanostructures were enhanced when the seed layers were annealed at $700^{\circ}C$. In addition, the full width at half maximum (FWHM) of near-band-edge emission (NBE) peak was decreased from 139 to 129 meV by increasing the annealing temperature to $700^{\circ}C$. However, the FWHM was slightly increased again by a further increase in the annealing temperature. Optical transmittance in the UV region was almost zero, while that in the visible region was gradually increased as the annealing temperature increased to $700^{\circ}C$. The optical band gap of the ZnO nanostructures was increased as the annealing temperature increased to $700^{\circ}C$. It is found that the optical properties as well as the structural properties of the rod-shaped ZnO nanostructures grown on R-plane sapphire substrates by hydrothermal method are improved when the seed layers are annealed at $700^{\circ}C$.