Preparation method of AlSiMg cast alloys with improved tensile strength properties and elongation

본 발명은 인장강도와 연신율이 향상된 AlSiMg 합금에 관한 것으로서, 보다 상세하게는 불순물로 Fe이 함유된 AlSiMg 합금에 있어서, 인장강도와 연신율을 향상시키기 위해 크롬 및 망간을 포함하는 AlSiMg 합금에 관한 것이다.본 발명은, 자동차 알루미늄 휠 합금으로 주로 사용되고 있는 AlSiMg 내에 혼입되어 합금의 인장성질을 저하시키는 불순물 Fe를 오히려 인장성질과 신율을 향상시키는 인자로 변화하도록 합금의 화학적 조성을 개량하여 인장강도와 연신율을 향상시킬 수 있는 알루미늄합금 제공을 목적으로 한다.본 발명은 불순물로 Fe이 함유된 AlSiMg 합금에 있어서, 인장강도와 연신율을 향상시키기 위해 크롬(Cr) 0.01∼0.20중량％ 및 망간(Mn) 0.02∼0.40중량％ 포함하는 AlSiMg 합금을 나타낸다. 본 발명에서 크롬, 망간 및 불순물인 Fe가 첨가되지 않은 AlSiMg 합금은 Al을 베이스로 하고, 6.5∼7.5중량％Si, 0.25∼0.45중량％Mg을 포함하는 AlSiMg 합금을 나타낸다

density functional theory and molecular dynamics studies

학위논문(박사) - 한국과학기술원 : 신소재공학과, 2009. 8., [ ix, 204 p. ]“Trial and Error” the traditional experimental synthesis and subsequent analysis of catalysts has been a widely applied strateagy in designing new heterogeneous catalysts. In this thesis, I use a computational approach, as a substitute of erroneous and time consuming experimental method, to study several interesting and most hot topics in the field of heterogeneous catalyst. Computational approach allows us to separately study a complex reaction pathway and to analyze the effect of a structure, composition, and a dimension of a catalyst. On account of such benefits of computational method, I set an object of this study to “Catalyst activation by designed reaction center.” In Chaper 1, the combined computational method of a molecular dynamics, the modified basin-hopping Monte Carlo simulation, and the Density Functional Theory is applied to study an Ag-Pd bimetallic nano cluster. The temperature dependent structural evolution, the surface catalytic reaction, and the structure dependent catalytic activity of nano clusters are discussed. I show that a small Ag-Pd bimetallic nano cluster can be a robust catalyst for CO oxidation. Solute element acted not only a reaction modifier but also a structural stabilizer. In Chapter 2 and 3, I expand the scope of the study to metal oxide catalysts. In Chapter 2, doped metal oxides are suggested as a new kind of oxidation catalyst. The modified catalytic activity of V, Cr, Mo, W, or Mn doped $TiO_2$ catalyst is tested via CO oxidation. I propose the vacancy formation energy as a reaction descriptor. In Chapter 3, the reaction mechanism of methanol dehydrogenation catalyzed by $TiO_2$ supported VOx, MoOx, and CrOx catalysts is analyzed. The location of the reactive surface oxygen species is studied by a state-of-art Density Functional Theory.한국과학기술원 : 신소재공학과

The effects of Mn and Cr on the microstructures and mechanical properties of A356 alloy

학위논문(석사) - 한국과학기술원 : 신소재공학과, 2005.2, [ iv, 88 p. ]A356 secondary합금의 기계적 성질을 향상시키는 것에 초점을 맞추어 Mn과 Cr을 첨가하면서 A356합금의 미세구조와 기계적 성질에 미치는 영향을 조사하였다. Mn과 Cr은 A356합금의 정출상과 석출상의 형성과 형상에 영향을 미쳤으며, A356 secondary합금에서 주로 나타나는 침상의 Fe관련 상의 생성을 방해하고, 새로운 석출상을 형성하였다. 이러한 Mn과 Cr의 영향은 합금의 미세조직을 개선하고 그 결과 기계적특성(인장특성)이 향상되는 결과로 나타났다. Mn과 Cr의 영향을 종합하여 secondary 합금의 기계적 성질을 개선할 수 있는 최적 조성을 설정하였으며, 이러한 합금조성을 활용할 경우 제품생산과정에서 상당한 생산원가 절감효과를 누릴수 있을 것으로 보인다.한국과학기술원 : 신소재공학과

Effects of substrate stiffness on shear stress induced motility of vascular endothelial cells

Vascular endothelial cell (VEC) forms a monolayer on the smooth muscle cell layer of blood vessel. Thus, substrate stiffness should be considered as one of the most important element in mimicking the physiological condition of VECs. In this research, the effect of substrate stiffness on shear stress induced cellular motility was investigated. VECs are seeded on polydimethylsiloxane (PDMS) substrate with controlled stiffness, ranging from 1.78 ㎫ to 48 ㎪. Shear stress system based on parallel plate flow chamber is utilized to apply laminar shear stress of 15 dyne/㎠. In order to explain the detailed mechanism of cellular migration, expression and distribution of cytoskeleton related pathway consisting RhoA, Rac1 and Cdc42 are examined. In addition, the regulation of syndecan-4 is observed as a mechanoreceptor. Results reveal that there is an optimal stiffness in maximizing the cell motility

Differential response of cancer cells to atmospheric plasma treatment in mammary gland epithelial cells

Atmospheric pressure plasma treatment has gained much attention in biomedical applications due to its selective activation of certain cell types. In this study, we compare cancer to normal cells of mammary gland (MDA-MB-231 vs. MCF-10A) to investigate the cellular responses to plasma in a cancer dependent manner. When treated with atmospheric pressure plasma at the input voltage of 1000 V for 2 minutes, MDA-MB-231 started to detach from the extracellular matrix while normal MCF-10A remained intact. Similarly to the plasma treated cases, high concentration of H₂O₂ provoked MDA-MB-231 cells to detach from the substrate in a few minutes while MCF10A cells were minimally perturbed. Moreover, immunostaining results from both plasma treated samples and H₂O₂ treated samples share a lot of features, confirming that the underlying mechanism behind plasma induced detachment is most likely due to reactive oxygen species in the plasma