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논문 : 제조공정 ; SCM 440 빌렛트의 수평 연속주조시 표면품질에 미치는 인발 사이클과 주조속도의 영향
이병화 ( B. H. Lee ),유병돈 ( B. D. You ),김목순 ( M. S. Kim ),정일권 ( I. K. Jung ),윤황로 ( H. R. Yoon ) 대한금속재료학회 ( 구 대한금속학회 ) 1998 대한금속·재료학회지 Vol.36 No.7
Trial tests were made to examine the effects of casting pattern on the surface quality of SCM 440 billets in horizontal continuous casting. The withdrawal cycle and the casting speed were varied 40~80 cycle/min and 0.7~1.0 m/min respectively. The main results obtained could be summarized as follows: When the withdrawal cycle is low, the withdrawal mark is irregular and the surface of billet is rough due to the formation of the lapped skin. The increase of withdrawal cycle results in the uniform withdrawal mark and the fine surface of cast products. The very low or the very high withdrawal cycle is essential for the prevention of transverse cracks on surface and corner cracks of the billet. For the case of the withdrawal cycle of 50 cycle/min, the effects of casting speed on the formation of transverse cracks and on the surface roughness could not be justified accurately due to the formation of lapped skin. The casting speed does not affect, however, the formation of the corner crack.
민경원,김현종,한명근,류태우,김목순,주영환,Min, Kyoung-Won,Kim, Hyun-Jong,Han, M.K.,U, Yu-Tae,Kim, Mok-Soon,Chu, Young-Hwan 한국전기화학회 2008 한국전기화학회지 Vol.11 No.4
본 연구에서는 백금의 입자크기가 내구성과 활성에 미치는 영향을 고찰하였다. 상용 Pt/C의 열처리를 통해 백금 입자 크기를 $3.5{\sim}9\;nm$로 조절하였고, XRD와 TEM을 통해 이를 확인하였다. 촉매의 내구성 분석을 위해 가속 실험을 실시하였고, 촉매 활성 측정을 위해 산소환원반응 실험을 하였다. 백금의 입자크기를 증가시킬수록 내구성은 향상되었으나 촉매의 활성이 저하되었다. 즉 촉매의 내구성과 활성은 반비례관계가 성립된다는 것을 확인하였다. 그리고 저하된 촉매 활성과 내구성을 향상시키기 위해, 합금 촉매를 사용하였다.상용 Pt/C의 최대 전력 밀도는 약 $507.6\;mV/cm^2$ 이고, PtCo/C 합금촉매는 $585.8\;mV/cm^2$이었다. 전기화학적 표면적은 상용 Pt/C는 약 60%정도 감소하였고, PtCo/C 합금촉매는 약 24%정도의 감소율을 나타냈다. 따라서 백금의 입자 크기 조절과 합금화를 통해 백금의 내구성과 활성을 동시에 높일 수 있었다. The influence of the particle size of platinum(Pt) on the stability and activity was studied. The particle size of platinum was controlled in the range of $3.5{\sim}9\;nm$ by heat treatment of commercial Pt/C and confirmed by XRD and TEM. An accelerated degradation test was performed to evaluate the stability of platinum catalysts. Oxygen reduction reaction was monitored for the measurement of activity. As increasing the Pt particle size, the stability of Pt/C electrode was enhanced and the activity was reduced. It was confirmed that the stability of Pt/C electrode was in inverse proportion to the activity. PtCo/C alloy catalyst was used to improve the activity and stability of large-sized platinum particle. The maximum power density of commercial Pt/C was $507.6\;mV/cm^2$ and PtCo/C alloy catalyst was $585.8\;mV/cm^2$. The decrement of electrochemical surface area showed Pt/C(60%) and PtCo/C alloy catalyst(24%). It was possible to enhance both of stability and activity of catalyst by the combination of particle size control and alloying.