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권용중,김동준 한국위험물학회 2018 한국위험물학회지 Vol.6 No.2
It is very important to classify explosion hazardous area in order to prevent an accident explosion. In order to prevent such a explosion, the Industrial Safety and Health Standards Rules stipulates the establishment and management of explosion hazards in accordance with the criteria set by the Korean Industrial Standards. This study has investigated the range of the explosion hazardous area according to various hole sizes, pressures, vapor densities, and wind velocities in the outdoor flammable liquid tank using KS C IEC-60079-10-1 2nd Ed.(=IEC CODE) and PHAST. The results show that the explosion hazardous areas by IEC CODE have circle shapes. However, the areas by PHAST show ellipse shapes. The different of the explosion hazardous areas increases with the increase of wind velocity.
3종의 CAD/CAM 시스템에서 지르코니아 코어의 변연 적합도에 관한 비교 연구
권용중,이영수,박원희,Kwon, Yong-Joong,Lee, Young-Soo,Park, Won-Hee 대한치과보철학회 2008 대한치과보철학회지 Vol.46 No.1
최근 개발된 다양한 CAD/CAM 시스템으로 제작된 지르코니아 코어의 변연 적합도에 관해 많은 연구가 있었다. 그러나 비교 연구는 미흡한 실정이다. 본 연구의 목적은 3종의 CAD/CAM 시스템에서 단일 전부 도재관을 위한 지르코니아 코어의 변연 적합도를 비교하는 것이다. 실험을 통하여 3종의 CAD/CAM 시스템($Adens^{(R)}$ 시스템, $Lava^{(R)}$ 시스템, $Cerasys^{(R)}$ 시스템) 으로 제작된 지르코니아 코어의 변연 적합도를 비교하였다. 각 시스템당 10개의 지르코니아 코어를 제작하였다. 광학현미경($L-150A^{(R)}$, Nikon, Japan)을 사용하여 총 50곳의 변연 간격을 측정하였다. 통계처리는 Kruskal Wallis test와 Wilcoxon Rank Sum test를 시행하였다. 단일 전부 도재관을 위한 지르코니아 코어의 총 변연간격은 $Adens^{(R)}$ 시스템이 $284.5{\pm}152.9{\mu}m$, $Lava^{(R)}$ 시스템이 $99.0{\pm}73.0{\mu}m$, 그리고 $Cerasys^{(R)}$ 시스템이 $153.5{\pm}85.7{\mu}m$ 이었다. 본 연구내에서, $Lava^{(R)}$ 시스템이 다른 시스템에 비해 우수한 변연 적합도를 보였다. Statement of problem: There have been many studies about marginal adaptation of Zirconia core fabricated with various CAD/CAM systems. But, the comparative study has not been conducted much. Purpose: This study was to compare marginal adaptations of zirconia cores fabricated with 3 different CAD/CAM systems. Material and methods: The in vitro marginal adaptations of zirconia cores fabricated with 3 different CAD/CAM systems($Adens^{(R)}$ system, $Lava^{(R)}$ system, and $Cerasys^{(R)}$ system) were evaluated and compared. In this study 30 zirconia cores were fabricated(10 zirconia cores per each system). The measurements of the marginal adaptatioin were carried out using microscope $L-150A^{(R)}$(Nikon, Japan). Measurements were recorded at 50 points. The measurements were analyzed using Kruskal-Wallis test and Wilcoxon rank sum test. Results: Within the limits of this study, the results were as follows. 1. Mean marginal gap values obtained were $284.5{\pm}152.9{\mu}m$ in Adens system, $99.0{\pm}73.0{\mu}m$ in Lava system, and $153.5{\pm}85.7{\mu}m$ in Cerasys system. 2. Zirconia core made by Lava system showed the smallest marginal gap(P<0.05). Conclusion: In the limitation of this study, we concluded that $Lava^{(R)}$ System was superior than other systems($Adens^{(R)}$ system and $Cerasys^{(R)}$ system) in the marginal adaptation.
권용중,Ali mirzaei,나한길,강성용,최명식,방재훈,이재갑,강인필,김상섭,김현우 대한금속·재료학회 2017 대한금속·재료학회지 Vol.55 No.7
Pt-functionalized RGO samples were prepared and subsequently irradiated with 2-MeV electron beams (e-beams). The effect of e-beam dose on the structural, electrical, and gas sensing properties of the samples was investigated. E-beam irradiation was found to induce significant microstructural changes in the Pt-functionalized RGO. Measurements of NO2 sensing at room temperature showed that the dose of 100 kGy led to better NO2 sensing properties compared to those of unirradiated sensors. On the other hand, the dose of 500 kGy appeared to be excessive, leading to extensive damage of the RGO structure and a significant reduction in the response to NO2 gas. E-beam irradiation can be beneficial for improving the gas sensing of Pt-functionalized RGO, but its dose needs to be optimized to obtain the best sensing properties.
Decoration of Ag nanoparticles on reduced graphene oxide and their application to gas sensors
나한길,권용중,강성용,강우승,최명식,방재훈,정택균,이종무,김현우 한양대학교 세라믹연구소 2016 Journal of Ceramic Processing Research Vol.17 No.6
We fabricated functionalized RGO that demonstrates excellent sensitivity to H2S gas. The functionalization process used GOsuspensions mixed with AgNO3, NaOH, and DI water. X-ray diffraction (XRD) and transmission electron microscopyindicated that the functionalizing structures were composed of cubic Ag and silver oxide (AgxOy) phases. Nanoparticles andnanorods with a cubic Ag phase were attached to the surface of the RGO. Raman spectra revealed that the structural disorderof the functionalized RGO was higher than that of pristine GO. The decrease of resistance by the introduction of H2S gasindicated that the functionalized RGO was an n-type sensor. Accordingly, we suggested that the n-type AgxOy, whose presencewas confirmed by XRD, should be a main current path for the sensor. A H2S gas sensing test revealed that the sensor responseat 50 ppm was about 1.65. With respect to H2S sensing mechanisms, we propose that the following four reasons could explainthe significant enhanced sensitivity by the functionalization: (i) reduction of the conduction volume by the conduction throughthe AgxOy structure rather than RGO, (ii) generation of silver sulfide structures, (iii) generation of an n-AgxOy/p-RGOheterointerface, and (iv) larger surface area of Ag/AgxOy structures. The Ag catalyst is not only the source of the AgxOy, butalso provides the spillover effect.
Simple fabrication and characteristics of Zn2Ti3O8 one-dimensional nanostructures
남상원,권용중,조홍연,강성용,나한길,김현우 한양대학교 세라믹연구소 2015 Journal of Ceramic Processing Research Vol.16 No.4
For the first time, we report the fabrication of one-dimensional (1D) nanostructures of Zn2Ti3O8. We heated the TeO2/TiO2 core-shell nanowires in a Zn-containing environment. The variation in heating temperature drastically changed the morphology and structure of the composite nanowires, obtaining the 1D nanostructures of Zn2Ti3O8 at 700 ℃. A photoluminescence (PL) study indicated that annealing at 700 ℃ generated a PL band at 2.5 eV in the green region, originating from the Zn2Ti3O8 structure. These findings may pave the way to fabrication and applications of novel composite nanostructures.
나한길,곽동섭,권용중,Fan Xia,박원일,김현우 한양대학교 세라믹연구소 2012 Journal of Ceramic Processing Research Vol.13 No.2
We have investigated the effects of the oxygen gas flow ratio in a synthesis process, ultimately producing thin (~40 nm in diameter) SnO2 nanowires. Scanning electron microscopy revealed that the oxygen partial pressure affected the diameter as well as the length of the nanowires. An X-ray diffraction investigation suggested that the grain size of the SnO2 phase was slightly increased with a decrease in the oxygen partial pressure. Lattice-resolved transmission electron microscopy (TEM)images, selected area electron diffraction, and micro-Raman spectroscopy coincidentally showed that the as-synthesized nanowires comprised a tetragonal SnO2 phase. Based on the analysis by fabricating field effect transistors, we found that the transport properties of SnO2 nanowires exhibited an n-type semiconductor characteristic.
TiO2/SiOx Core-Shell Nanowires Generated by Heating the Multilayered Substrates
나한길,곽동섭,권용중,조홍연,이종무,김현우 대한금속·재료학회 2013 METALS AND MATERIALS International Vol.19 No.4
By heating Au/TiN/Si substrates, we fabricated TiO2/SiOx core-shell nanowires. By changing the thickness of predeposited Au layers, we demonstrated that the thickness of the Au layer needs to be optimized to obtain nanowires. High-resolution transmission electron microscopy image, X-ray diffraction spectrum,and selected area electron diffraction pattern coincidentally revealed that the resultant core nanowires had a tetragonal rutile structure of TiO2, and the shell was comprised of amorphous SiOx. The dominant growth mechanism was a base-growth mode, in which Au played a catalytic role, resulting in morphological changes with variation of the Au layer thickness. The TiO2/SiOx core-shell nanowires exhibited a broad photoluminescence emission band, which comprised four peaks centered at 1.54, 2.34, 2.67, and 2.99 eV,respectively. We expected that the 1.54 eV- and 2.34 eV-centered peaks arised from the TiO2 core, whereas the 2.67 eV- and 2.34 eV-peaks were ascribed to both the TiO2 core and the SiOx shell.