• Applied Chemistry for Engineering
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• v.32 no.4
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• pp.442-448
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• 2021

Flow field is an important parameter for polymer electrolyte membrane fuel cell (PEMFC) performance to have an effect on the reactant supply, heat and water diffusion, and contact resistance. In this study, PEMFC performance was investigated using Cu foam flow field at the cathode of 25 cm² unit cell. Polarization curve and electrochemical impedance spectroscopy were performed at different pressure and relative humidity conditions. The Cu foam showed lower cell performance than that of serpentine type due to its high ohmic resistance, but lower activation and concentration loss due to the even reactant distribution of porous structure. Cu foam has the advantage of effective water transport because of its hydrophobicity. However, it showed low membrane hydration at low humidity condition. The metal foam flow field could improve fuel cell performance with a uniform pressure distribution and effective water management, so future research on the properties of metal foam should be conducted to reduce electrical resistance of bipolar plate.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.377-381
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• 2004

Electrical conductivity of Al-Si-Cu-Mg alloy foams of various density produced in powder metallurgical method has been measured using two probe electrical conductivity measurement method. Compressive mechanical properties such as elastic modulus and plastic plateau stress of foams were evaluated from electrical conductivity using power law relation and scaling laws of foam properties. Uni-axial compression test was also performed. Experimentally measured elastic modulus and plastic plateau stress were compared with the values evaluated from electrical conductivity. The computed values were in good agreement with the experimental result.

• Journal of Mechanical Science and Technology
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• v.20 no.6
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• pp.819-827
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• 2006

The stress-strain relation of aluminum (Al) alloy foam cell wall was evaluated by the instrumented sharp indentation method. The indentation in a few micron ranges was performed on the cell wall of Al-alloy foam having a composition or Al-3wt.%Si-2wt.%Cu-2wt.%Mg as well as its precursor (material prior to foaming). To extract the stress-stram relation in terms of yield stress ${\sigma}_y$, strain hardening exponent n and elastic modulus E, the closed-form dimensionless relationships between load-indentation depth curve and elasto-plastic property were used. The tensile properties of precursor material of Al-alloy foam were also measured independently by uni-axial tensile test. In order to verify the validity of the extracted stress-strain relation, it was compared with the results of tensile test and finite element (FE) analysis. A modified cubic-spherical lattice model was proposed to analyze the compressive behavior of the Al-alloy foam. The material parameters extracted by the instrumented nanoindentation method allowed the model to predict the compressive behavior of the Al-alloy foam accurately.

• Korean Journal of Materials Research
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• v.23 no.7
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• pp.366-372
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• 2013

Flexible polyurethane/clay porous nanocomposite foams were synthesized using natural and organically modified montmorillonite clays such as bentonite, closite 10A and closite 30B. The content of nanoclays was varied from 1 to 5 wt% of polyol. Dispersion of clay in Polyurethane(PU) matrix was investigated by X-ray diffraction(Cu-$K{\alpha}$ rays of wavelength $1.54{\AA}$) using an X-ray diffractometer. Also, we determined that the thermal resistance of PU foam increased with added clay, compared to that of pure PU foam. The cell size and the fraction of open cells of the precursor foam were controlled by the addition of clay to the polyurethane foam. Modified clays were found to be more efficient cell openers than the unmodified clay. In addition, the tensile strength and elongation of the polyurethane/clay porous nanocomposites were examined. Increasing clay content increased the mechanical properties of the composites, such as tensile strength, and elongation at break. However, increasing the content over 5 wt% deteriorated the properties of the composites. We found that the nanofillers(bentonite, closite 10A and closite 30B) improved the thermal stability of the nanocomposite foam. The nanocomposite foam containing 3 wt% of closite 30B exhibited the best tensile strength and thermal stability.

• Transactions of Materials Processing
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• v.12 no.6
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• pp.588-596
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• 2003

The relationships between evolution of microstructure and mechanical properties of porous Al-3Si-2Mg-2Cu alloy after the foaming and various heat treating were investigated. The foamed alloy having various densities were manufactured by powder compact foaming and heat treated. Then compression test was performed with deformation rate of 0.5/s. The ultimate compression strength was not changed after solution heat treatment but the flow curve after ultimate strength showed very smooth and uniform plateau region. This change of flow curve means that the deformation mechanism is altered from brittle fracture to ductile deformation and the energy absorption property of Al foam is dramatically improved. The improvement of energy absorption without any detriment of mechanical properties is due to that the very brittle precipitation like Al-Cu and Al-Mg was uniformly dissolved in Al matrix after solution heat treatment. And various mechanical properties of Al alloy porous material were improved by 40% with aging of $200^{\circ}C$ and 50min. These improvements are ascribe to the various fine precipitates like $\Omega$ and $\theta$'.

• Journal of Nutrition and Health
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• v.36 no.9
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• pp.908-917
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• 2003

It has been proposed that oxidative modification of LDL (oxLDL) plays a significant role in the pathogenicity of atherogenesis. We tested the hypothesis that chitin and chitosan may function as antioxidants with respect to 0.1 mg cholesterol/ml LDL incubated with 5 $\mu$ M Cu$^2$$^{+}$alone or in the P338Dl mouse macrophage system using L-ascorbic acid as a standard classical antioxidant. The degree of oxLDL formation was ascertained by the relative electrophoretic mobility (rEM) in the combination of thiobarbituric acid reactive substances (TBARS) levels, and the cytotoxicity of oxLDL was detected by macrophage viability. The oxLDL uptake and foam cell formation of macrophages were measured by Oil Red O staining. Incubation with Cu$^2$$^{+}$and macrophages increased rEM of LDL and stimulated TBARS formation. Culture of macrophages with LDL in the presence 5 $\mu$ M Cu$^2$$^{+}$induced macrophage death. In cell-free system 200 $\mu$g/ml water-soluble chitosan and chitosan-oligosaccharide blocked oxLDL formation. Water-soluble chitosan and chitosan-oligosaccharide blocked oxLDL formation near-completely relative to L-ascorbic acid, whereas water-soluble chitin and chitin-oligosaccharide had no measurable antioxidant effect. In macrophage system water-soluble chitosan and chitosan-oligosaccharide blocked oxidation of LDL with a significant increase in cell viability, and decreased TBARS in medium. As for the inhibitory effect on macrophage foam cell formation, chitosan and its oligosaccharide, but not watersoluble chitin, revealed the effectiveness. The endothelial expression of lectin-like oxLDL receptor-1 (LOX-1) was tested by Western blot analysis, and chitosan, chitosan-oligosaccharide and chitin-oligosaccharide blocked LOX-1 expression. These results indicate that water-soluble chitosan and its oligosaccharide showed the inhibitory effect on Cu$^2$$^{+}$-induced LDL oxidation of macrophages, and chitosan, chitosan-oligosaccharide and chitin-oligosaccharide had blocking effect on oxLDL receptor expression in the human umbilical vein endothelial system. Thus, water-soluble chitosan and its oligosaccharides possess anti-atherogenic potentials possibly through the inhibition of macrophage LDL oxidation or endothelial oxLDL receptor expression depending on chemical types.l types.

• 한국태양에너지학회:학술대회논문집
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• 2012.03a
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• pp.260-266
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• 2012

Syngas and hydrogen from the $CeO_2/ZrO_2$ coated foam devices were investigated under simulated solar radiation. The $CeO_2/ZrO_2$ coated SiC, Ni and Cu foam device were prepared using drop-coating method. Syngas production step was performed at $900^{\circ}C$, and hydrogen production process was performed for ten repeated cycles to compare the CeO2 conversion in syngas production step, $H_2$ yield in hydrogen production step and cycle reproducibility. The produced syngas had the $H_2$/CO ratio of 2, which was suitable for methanol synthesis or Fischer-Tropsch synthesis process. In addition, syngas and hydrogen production process is one of the promising chemical pathway for storage and transportation of solar heat by converting solar energy to chemical energy. After ten cycles of redox reaction, the $CeO_2/ZrO_2$ was analyzed using XRD pattern and SEM image in order to characterize the physical and chemical change of metal oxide at the high temperature.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.434-437
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• 2005

Chemical Mechanical Polishing (CMP) has become an essential step in the overall semiconductor wafer fabrication technology. In general, CMP is a surface planarization method in which a silicon wafer is rotated against a polishing pad in the presence of slurry under pressure. The polishing pad, generally a polyurethane-based material, consists of polymeric foam cell walls, which aid in removal of the reaction products at the wafer interface. It has been found that the material removal rate of any polishing pad decreases due to the so-called 'pad glazing' after several wafer lots have been processed. Therefore, the pad restoration and conditioning has become essential in CMP processes to keep the urethane polishing pad at the proper friction coefficient and to allow effective slurry transport to the wafer surface. Diamond pad conditioner employs a single layer of brazed bonded diamond crystals. Due to the corrosive nature of the polishing slurry required in low pH metal CMP such as copper, it is essential to minimize the possibility of chemical interaction between very low pH slurry (pH <2) and the bond alloy. In this paper, we report an exceptional protective coated conditioner for in-situ pad conditioning in low pH Cu CMP process. The protective Cr-coated conditioner has been tested in slurry with pH levels as low as 1.5 without bond degradation.

• Journal of Industrial and Engineering Chemistry
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• v.68
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• pp.161-167
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• 2018

In this study, transition metal coated carbon nanofibers (CNFs) were synthesized and applied as anode materials of Li secondary batteries. CNFs/Ni foam was immersed into 0.01 M transition metal solutions after growing CNFs on Ni foam via chemical vapor deposition (CVD) method. Transition metal coated CNFs/Ni foam was dried in an oven at $80^{\circ}C$. Morphologies, compositions, and crystal quality of CNFs-transition metal composites were characterized by scanning electron microscopy (SEM), Raman spectroscopy (Raman), and X-ray photoelectron spectroscopy (XPS), respectively. Electrochemical characteristics of CNFs-transition metal composites as anodes of Li secondary batteries were investigated using a three-electrode cell. Transition metal/CNFs/Ni foam was directly employed as a working electrode without any binder. Lithium foil was used as both counter and reference electrodes while 1 M $LiClO_4$ was employed as the electrolyte after it was dissolved in a mixture of propylene carbonate:ethylene carbonate (PC:EC) at 1:1 volume ratio. Galvanostatic charge/discharge cycling and cyclic voltammetry measurements were taken at room temperature using a battery tester. In particular, the capacity of the synthesized CNFs-Fe was improved compared to that of CNFs. After 30 cycles, the capacity of CNFs-Fe was increased by 78%. Among four transition metals of Fe, Cu, Co and Ni coated on carbon nanofibers, the retention rate of CNFs-Fe was the highest at 41%. The initial capacity of CNFs-Fe with 670 mAh/g was reduced to 275 mAh/g after 30 cycles.

• Carbon letters
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• v.17 no.1
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• pp.65-69
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• 2016