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Preparation of Bimodal Porous Carbon Supported PtRu Catalysts for Fuel Cells
Hwang, S.,Park, G.-G.,Yim, S.-D.,Park, S.-H.,Yang, T.-H.,Kim, H.,Kim, C.-S. WILEY-VCH Verlag 2010 FUEL CELLS -WEINHEIM- Vol.10 No.2
<P>In this work, we synthesised the bimodal porous carbon supported electro-catalyst as a novel catalyst for fuel cells. For this purpose, the bimodal porous carbons with different pore sizes were prepared by imprinting method. Three kinds of bimodal porous carbons were fabricated by using the silica spheres with diameters of ca. 50, 100 and 300 nm and SBA-15 particle having 200–250 nm diameter and 700–900 nm length as templates. The BET surface areas of the bimoal porous carbons were determined to be 235–294 m<SUP>2</SUP> g<SUP>–1</SUP>, which are similar to that of Vulcan XC72. To evaluate the electro-catalytic activity, the PtRu nanoparticles of ca. 1.9–2.6 nm were loaded on the bimodal porous carbon supports. The PtRu/C100, synthesised by using SBA-15 and 100 nm silica sphere, had the higher electrochemical surface area (ECSA) and the lower on-set potential and showed comparable performance with the commercial catalyst.</P>
DED 공정을 이용한 적층 경로 및 재료에 따른 잔류응력 특성 분석
임성훈(S. H. Yim),이광규(K. K. Lee),안동규(D.-G. Ahn) Korean Society for Precision Engineering 2021 한국정밀공학회 학술발표대회 논문집 Vol.2021 No.11월
DED 공정에서의 잔류응력은 국부적이고, 급격한 열이력에 의해 발생한다. 잔류응력 저감 방법에 대한 연구가 진행되고 있지만 적층 경로와 적층 재료 와의 관계에 대한 연구는 부족하다. 이 연구에서는 DED 공정을 이용한 실험 및 3 차원 열-기계 연계 유한요소 해석을 통해 적층 경로 및 적층 재료에 따라 나타나는 잔류응력 특성을 분석하고자 한다. 적층 실험은 단일, 다열 및 다층 순으로 진행되었으며, SCM 440 위 G6 및 SUS316L 위 SUS316L 적층 시편을 제작하였다. 유한요소 해석 모델은 실험 결과 도출된 적층부 특성데이터를 이용하여 생성하였으며, 해석은 상용 소프트웨어인 SYSWELD V15.5 를 이용하였다. 해석에 적용된 물성데이터는 JmatPro V12.0 를 통해 도출된 온도 의존 열 물성을 적용하였다. 실험 조건을 기반으로 자연대류, 등가 열 손실 계수 도출 및 고정 경계조건을 해석모델에 적용하였다. 단일 비드 및 다열 비드 해석을 통해 도출된 열원 효율을 기반으로 적층 경로에 따라 10 × 10 mm 4 층 열-기계 해석을 진행하였다. 응력 분포, 최대 응력 발생 위치, 응력 변화 및 열 이력을 도출 하였으며, 적층 경로 및 적층 재료에 따라 적층부 및 적층부 주변에 발생하는 잔류응력 특성을 비교분석을 통해 적층 재료 별 잔류응력이 최소화 되는 적층 경로를 선정 하였다. 또한, 적층 재료에 따라 적정 적층 경로가 상이하다는 것을 알 수 있었다.
열처리에 따른 함인 구상흑연주철의 Steadite 분포와 내마멸특성 변화
김동규,나형용,서상철,임창희 대한금속재료학회(대한금속학회) 1991 대한금속·재료학회지 Vol.29 No.5
The steadite enveloping heat treatement and wear test were carried out in order to investigate the distribution of steadite and wear characteristics of phosphorus contained ductile cast iron. The steadite existed among eutectic cell boundaries was moved to the graphite and appeared to envelop graphite at the optimum steadite enveloping heat treatment condition of 1050℃ for 30 min. In the case of specimens not treated with steadite enveloping heat treatment, the maximum point of wear loss was moved to high velocity side with increasing phosphorus content, while the maximum point of wear loss did not appear clearly for the steadite enveloping heat treated specimens. The steadite enveloping heat treated specimen showed superior wear characteristics than the specimen not treated, due to the rein- forcement of hard steadite exists around soft graphite.
Fingerprint and weathering characteristics of stranded oils after the Hebei Spirit oil spill
Yim, U.H.,Ha, S.Y.,An, J.G.,Won, J.H.,Han, G.M.,Hong, S.H.,Kim, M.,Jung, J.H.,Shim, W.J. Elsevier Scientific Pub. Co 2011 Journal of hazardous materials Vol.197 No.-
After the Hebei Spirit oil spill in December 2007, mixtures of three types of Middle East crude oil were stranded along 375km of coastline in Western Korea. Stranded oils were monitored for their identity and weathering status in 19 stations in three provinces. The results obtained using a weathering model indicated that evaporation would be a dominant weathering process immediately after the spill and the sequential changes of chemical composition in the field verified this prediction positively. In the early stages of weathering, the half-life of spilled oil was calculated to be 2.6 months. Tiered fingerprinting approaches identified background contamination and confirmed the identity of the stranded oils with the spill source. Double ratios using alkylated phenanthrenes and dibenzothiophenes in samples after the spill clearly reveal the impact of weathering on oil. However, to derive defensible fingerprinting for source identification and allocation, recalcitrant biomarkers are extremely useful. Weathering status of the stranded oils was evaluated using composition profiles of saturated hydrocarbons, polycyclic aromatic hydrocarbons and various weathering indices. Most samples collected 8 months after the spill were categorized in either the advanced or extreme weathering states. Gradual increase in toxic components in the residual oil through weathering emphasizes the need for adaptive ecotoxicological approaches.
Forced Vibration Analysis of an IPM Motor for Electrical Vehicles due to Magnetic Force
Yim, K. H.,Jang, J. W.,Jang, G. H.,Kim, M. G.,Kim, K. N. IEEE 2012 IEEE transactions on magnetics Vol.48 No.11
<P>This paper discusses a method to analyze the forced vibration of an interior permanent magnet (IPM) motor due to magnetic force. A structural finite element (FE) model of the IPM motor that includes stiffness of ball bearings and laminated effect of core is developed and verified by comparing the simulated natural frequencies and mode shapes with experimental data. A magnetic FE model is also developed and both the radial and tangential magnetic forces are calculated in the air-gap. These forces are subsequently transformed into equivalent nodal forces and applied to the structural FE model to investigate the forced vibration characteristics of the IPM motor. It was found that the magnetically induced vibration of a stator mainly results from the contribution of the dominant harmonics of the magnetic force and structural resonance. In addition, the magnetically induced vibration of the rotor mainly appeared as rigid body modes due to the flexibility of ball bearings.</P>
The influence of stack clamping pressure on the performance of PEM fuel cell stack
Yim, S.D.,Kim, B.J.,Sohn, Y.J.,Yoon, Y.G.,Park, G.G.,Lee, W.Y.,Kim, C.S.,Kim, Y.C. Elsevier 2010 Current Applied Physics Vol.10 No.2
The effect of gas diffusion layer (GDL) compression on fuel cell performance was experimentally studied in a 5-cell proton exchange membrane fuel cell (PEMFC) stack. Two stacks with different GDL compression, 15% and 30%, were prepared using SGL 10BC carbon-fiber felt GDL and Gore 57 series MEA. The PEMFC stack with high GDL compression (30%) showed better performance than low GDL compression (15%) at all current ranges. This implies that the decrease of contact resistance by high GDL compression affects more dominantly on the stack performance than the increase of mass transport resistance in the present stack configurations. The degree of GDL compression also affected the stack stability, particularly, under the reformed gas conditions as anode fuel. The stack with low GDL compression could not be operated at low reformed gas flow rates showing sudden decrease of stack voltage. Hence, in case of reformed gas condition, GDL compression should be higher than the case of pure hydrogen for the stable stack operation and to enhance the gas utilization at anode.