• Korean Chemical Engineering Research
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• v.62 no.1
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• pp.1-6
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• 2024

As the demand for hydrogen electric vehicles for commercial vehicles increases, the durability of PEMFCs must increase more than five times that of passenger cars, so research and development to improve durability is urgent. When the PEMFC membrane electrode assembly (MEA) undergoes chemical degradation, the MEA thickness decreases and pinholes occur. In this study, changes in the performance and durability of the MEA were measured while increasing the clamping pressure of the unit cell after open circuit voltage (OCV) holding, an accelerated chemical degradation experiment. As the clamping pressure increased, the resistance of the polymer membrane and the membrane/electrode contact resistance decreased, improving the I-V performance and reducing the hydrogen permeability. As the hydrogen permeability decreased, the OCV increased. When the pinhole area was removed and the MEA clamping pressure was increased, the hydrogen permeability decreased sharply, confirming that the local degradation has a large effect on the performance and durability of the entire cell. When the pinhole was removed and re-clamping and OCV holding was evaluated, it was confirmed that the durability improved according to the decrease in membrane resistance and hydrogen permeability.

• Journal of Adhesion and Interface
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• v.9 no.1
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• pp.3-8
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• 2008

Self-sensing was evaluated for carbon nanofiber (CNF)/epoxy composites with two different aspect ratios via electro-micromechanical technique and wettability test. Volumetric electrical resistance was measured to evaluate the comparative dispersion degree indirectly and it decreased due to the increase of electric contacts with increasing CNF concentration. The dispersion degree was evaluated indirectly by calculating coefficient of variation (COV) of volumetric electrical resistance. The CNF type A with a high aspect ratio showed better self-sensing than the case of CNF type B with a short aspect ratio. The CNF type B/epoxy composite showed little self-sensing at a concentration higher than 2 vol% probably due to poor dispersion. The apparent modulus of CNF type B was higher than that of CNF type A due to the orientation effect and the high surface area. The thermodynamic work of adhesion was consistent with the result of apparent modulus.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.7
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• pp.4665-4674
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• 2014

The aim of this study was to confirm the feasibility of the electro-coagulation process as a pre-treatment for the membrane separation of anaerobic digestion effluents to minimize membrane fouling. The reduction of membrane fouling was evaluated according to the number of electrodes (immersed surface area of electrodes), current density and contact time. In the case of the small surface area of electrodes, the increased electric field strength resulted in a soluble COD increase due to the destruction of the microbial flocs and/or cells, whereas large changes in the soluble COD were not observed in the case of the high surface area of electrodes. On the other hand, the T-P concentration decreased as a result of the precipitation of aluminum ions and phosphates. The membrane permeation flux increased and the fouling resistance (Rc+Rf) decreased with increasing electric current density. Although the particle size of the anaerobic digestion effluent increased slightly, it was not related directly to the reduced fouling phenomena. The main mechanism for the enhanced flux was attributed to the inorganic particulate produced during electrocoagulation, such as $AlPO_4$, which acted as a dynamic membrane deposited on the membrane surface.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.5
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• pp.475-479
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• 2012

We present a novel polymer fabrication process involving direct UV patterning of a hyperbranched polymer, AEO3000. Compared to PDMS, which is the most widely used polymer in bioMEMS devices, the present polymer has advantages with regard to electrode integration and fast fabrication. We designed a four-chip microelectrofluidic bench having three electrical pads and two fluidic I/O ports. We integrated a microfluidic mixer and a cell separator on the bench to characterize the interconnection performance and sample manipulation. Electrical and fluidic characterization of the microfluidic bench was performed. The measured electrical contact resistance was $0.75{\pm}0.44{\Omega}$, which is small enough for electrical applications, and the pressure drop was 8.3 kPa, which was 39.3% of the value in the tubing method. By performing yeast mixing and a separation test in the integrated module on the bench, we successfully showed that the interconnected chips could be used for bio-sample manipulation.

• Polymer(Korea)
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• v.36 no.2
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• pp.155-162
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• 2012

Sulfonated poly(ether ether ketone) (SPEEK) nanofibers were prepared by electrospinning. The nanofibrous membrane for polymer electrolyte membrane fuel cell (PEMFC) was fabricated by compression molding. The maximum degree of sulfonation was 95% and the initial thermal degradation temperature was $280^{\circ}C$ and it's value was lower than that of PEEK. The contact angle of SPEEK increased with decreasing the degree of sulfonation. The optimum voltage, flow rate, tip to collector distance (TCD) and concentration of electrospinning conditions were 22 kV, 0.3 mL/hr, 15 cm, and 23 wt%, respectively. The average nanofibrous diameter was 47.6 nm. The water uptake and ion exchange capacity of SPEEK nanofibrous membrane increased with increasing the sulfonation time and the amount of sulfonating agent. The electrical resistance and proton ionic conductivity of SPEEK membrane increased with decreasing and increasing the sulfonation time, respectively. Their values were 0.58~0.06 ${\Omega}{\cdot}cm^2$and 0.099 S/cm.

• Journal of Aerospace System Engineering
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• v.12 no.3
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• pp.64-69
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• 2018

The high-velocity electromagnetic forming (EMF) process is based on the Lorentz force and the energy of the magnetic field. The advantages of EMF include improved formability, wrinkle reduction, and non-contact forming. In this study, the electromagnetic-structural interlocking analysis was performed in order to analyze the moldability of aluminum pipe using electromagnetic molding. The magnetic flux density was decreased due to increasing electrical resistance as the temperature increased, and the stress-strain curve decreased. The higher the temperature, the lower the flow stress, increasing deformation.

• The Journal of Information Technology
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• v.7 no.2
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• pp.69-76
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• 2004

This paper presents the results of spectral analysis about waveforms and leakage current waveforms on contaminated silicon insulators under various environment conditions.(salt fog, clean fog, rain). The larger the leakage current during 200ms, the higher the power spectrum at 60Hz. If contaminated insulators suffers from high salt density fog, the leakage current occurs with high crest value intermittently, results in the low spectrum. Analysis of leakage current data showed that this electrical activity was characterized by transient arcing behavior contaminants are deposited on the insulator surface during salt fog tests. This provides a path for the leakage current to flow along the surface of the insulator. It is important to have an indication of the pollution accumulation in order to evaluate the test performance of a particular insulator. If the drop in surface resistivity is severe enough, then the leakage current may escalate into service interrupting flashover that degrade power quality.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.377-382
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• 2001

Mechanical behavior and electrical resistance change of CPDP (carbon particle dispersed plastic) composite consisting of epoxy resin and conductive carbon particle were investigated under monotonic loading and repeated loading-unloading. The electrical resistance almost linearly increased with increasing strain during loading and the residual electrical resistance was observed even after removing load. The value of the residual electrical resistance was dependent on the maximum strain under the applied stress. This result suggests that the estimation of maximum strain (i.e., damage) is possible by the measuring electrical resistance of composite. The behavior of electrical resistance change during and after loading was discussed on the basis of the results of microscopic deformation and fracture observation. Moreover, the relationship between the volume fraction of carbon particle and the electrical resistivity of CPDP was investigated in relation to the percolation theory. Simulation model of percolation structure was established by Monte Carlo method and the simulation result was compared to the experimental results. The electrical resistance change under applied loading was analyzed quantitatively using the percolation equation and a simple model for the critical volume fraction of carbon particle as a function of the mechanical stress. It was revealed that the prediction was in good agreement with the experimental result except in the region near the failure of material.

• Journal of the Korean Society for Railway
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• v.18 no.5
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• pp.410-418
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• 2015

A slider of the pantograph undergoes uneven and abnormal wear due to sliding contact with the catenary. In the case of rain, the loss of lubricant increases the frictional resistance for the reciprocating motion between the catenary and the slider, accelerating local wear. The slider in the winter should have good wear resistance, which can be achieved through alloy design. Uneven and abnormal wear were not observed in the results of a driving test using a wear resistant slider. It was found that the increased density of the slider enhanced the corrosive effects of Fe-Ti, preventing the occurrence of abnormal wear by maintaining the wear and arc resistance in the rainy season. Also, mechanical and electrical wear did not affect the composition of the slider, and this improved the wear resistance. Inaddition, the slider was applied to an entire train and was tested during driving; ananalysis of the correlation of the catenary was performed, including during the rainy season and the winter season.

• Journal of the Microelectronics and Packaging Society
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• v.17 no.1
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• pp.19-24
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• 2010

The effects of $O_2$ plasma pretreatment on the properties of Ga-doped ZnO films on PET substrate were studied. GZO films were fabricated by RF magnetron sputtering process. To improve surface energy and adhesion between the PET substrate and the GZO film, $O_2$ plasma pretreatment process was used prior to GZO sputtering. As the RF power and the treatment time increased, the crystallinity increased and the contact angle decreased significantly. When the RF power was 100 W and the treatment time was 600 sec in $O_2$ plasma pretreatment process, the resistivity of GZO films on the PET substrate was $1.90{\times}10^{-3}{\Omega}-cm$.