• Journal of the Korean Society for Precision Engineering
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• v.23 no.3 s.180
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• pp.47-55
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• 2006

Laser welding of dissimilar metals has been widely used to improve a wear resistance and a corrosion resistance of the industrial parts. The objective of this research is to investigate the influence of the process parameters, such as the welding for SM45C and STS304 with CW Nd:YAG lasers. The bead-on-plate welding tests are carried out for several combinations of the experimental conditions. In order to quantitatively examine the characteristics of the dissimilar welding, the welding quality of the cut section, stress-strain behavior and the hardness of the welded metal are investigated. From the results of the investigation, it has been shown that the optimal voiding condition without defects in the vicinity of the welded area and with a good welding quality is 1600W of the laser power, 0.85m/min of welding speed and $4{\ell}/min$ of pressure for shielding gas.

• Journal of Korean Society of Water and Wastewater
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• v.28 no.4
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• pp.441-451
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• 2014

The flushing is important to maintain good water quality in water main. It is a technique of using water velocity to remove sediments in water distribution system. The variety of water quality problems can occur in a distribution system, so too can a variety of benefits be gained by system flushing. In order to effectively perform the flushing, the contaminants to be removed to set up and it can be solved, it is necessary to ensure the proper flow rate. In this study, the removal of contaminants present in the inner water pipe attached loose deposits such as fine particles of granular activated carbon, sand and iron corrosion product sought to derive flow rates. Thus, the constant observation of using pilot plant scale water distribution plant for the movement of floating characteristics of particles were assessed.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.11.2-11.2
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• 2011

A key technological issue related to the implementation of dye-sensitized solar cells (DSSCs) is the replacement of Pt at the counter electrodes with an inexpensive and electro-chemically stable alternative. Carbon based nanomaterials could be promising candidates, but in practice they exhibit inadequate device performance. Here, we report very thin graphene oxide (GO)/metal hybrid films as transparent counter electrodes for high-efficiency DSSCs. Transparent GO/Pt and GO/Au hybrid films showed cell efficiencies of 9.2 and 9.0%, respectively (improvements of 9.5 and 7.1% over conventional Pt counter electrodes). More interestingly, highly stable DSSCs with GO hybrid films from relatively inexpensive metals such as Cu and Ni have been demonstrated with efficiency values comparable to Pt counter electrodes. The results reported in this study should enable low-cost fabrication of DSSCs because it allows the use of relatively inexpensive metals such as Au, Cu, Ni, and Ag that could not be previously employed in DSSCs with iodide/tri-iodide electrolyte due to corrosion.

• Korean Journal of Materials Research
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• v.16 no.3
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• pp.193-197
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• 2006

The sodium/sulfur(Na/S) battery has many advantages such as high theoretical specific energy(760Wh/kg), and low material cost based on the abundance of electrode material in the earth. It has been reported that the electrochemical properties of sodium/sulfur cell above $300^{\circ}C$, utilized a solid ceramic electrolyte and liquid sodium and sulfur electrodes. A lot of researches have been performed in this field. Recently, Na/S battery system was applied for electricity storage system for load-leveling. One of severe problems of sodium/sulfur battery was high operating temperature above $300^{\circ}C$, which could induce the explosion and corrosion by molten sodium, sulfur and polysulfides. In order to develop sodium battery operated at low temperature, sodium ion battery has been studied using carbon anode, and sodium oxides cathodes. However, the energy densities of the sodium ion batteries were much lower than high temperature sodium/sulfur cell. In this study, the sodium/sulfur battery with 1M $NaCF_3SO_3$ is tested at room temperature. The charge-discharge mechanism was discussed based on XRD, DSC, SEM and EDS results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.1
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• pp.8-17
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• 2003

Fracture behaviors of pipes with local wall thinning are very important for the integrity of nuclear Power Plant. In Pipes of energy Plants, sometimes, the local wall thinning may result from severe erosion-corrosion (E/C) damage. However, the effects of local wall thinning on strength and fracture behaviors of piping system were not well studied. In this paper, the monotonic bending tests were performed of full-scale carbon steel pipes with local wall thinning. A monotonic bending load was applied to straight pipe specimens by four-point loading at ambient temperature without internal pressure. From the tests, fracture behaviors and fracture strength of locally thinned pipe were manifested systematically. The observed failure modes were divided into four types; ovalization. crack initiation/growth after ovalization, local buckling and crack initiation/growth after local buckling. Also, the strength and the allowable limit of piping system with local wall thinning were evaluated.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.25 no.1
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• pp.68-74
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• 2016

The Nd:YAG laser welding process is one of the most advanced manufacturing technologies owing to its high speed and penetration, and has increased the automation and flexibility of an entire industry. Laser welding of dissimilar metals has been widely used to improve the wear resistance and corrosion resistance of industrial parts. The objective of this research is to investigate the influence of process parameters on the welding of SM45C and STS304 with CW Nd:YAG lasers. Bead-on-plate welding tests were carried out for several combinations of the experimental conditions. In order to quantitatively examine the characteristics of the dissimilar welding, the welding quality of the cut section, strain-stress behavior, and hardness of the welded part were investigated.

• 한국신재생에너지학회:학술대회논문집
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• 2007.06a
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• pp.335-338
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• 2007

Cost effectiveness is an important parameter for producing DSSCs as compared to the widely used conventional silicon based solar cells. A fluorine-doped tin oxide (FTO) substrate coated with a catalytic amount of platinum is used as counter electrode in dye-sensitized solar cell. Carbonaceous materials are quite attractive to replace platinum due to their high electronic conductivity, corrosion resistance towards $I_{2}$, good catalytic effect and low cost. In this paper, the unit DSSCs with Pt and CNT as a counter electrode were connected in series-parallel externally, then the current-voltage curves were investigated to find out the connection characteristics of the DSSC with CNT counter electrode. The connection characteristics of the DSSC with CNT counter electrode is superior to that of the DSSC with Pt counter electrode. And a parallel connection of the DSSC with CNT counter electrode has higher efficiency than a series connection of that.

• Journal of the Korean Society of Industry Convergence
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• v.10 no.4
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• pp.201-206
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• 2007

Most of the fatigue fractures of various machine structures start at discontinuities or small defects. In this study property of crack growth of titanium alloy was also analyzed to investigate the difference compared with the carbon steel. Titanium alloy has very high specific strength, and the material is widely utilized in advanced engineering fields such as aerospace, atomic energy and ocean development because of its excellence in corrosion and heat resistance. Generally the machine structures experience irregular loadings rather than periodic forces. The prediction of the fatigue life therefore has been analyzed to provide fundamentals of the design and estimation of the machine structures under irregular loading conditions.

• Journal of Welding and Joining
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• v.27 no.2
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• pp.27-31
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• 2009

Ferritic stainless steels have a good heat resistance and economic advantage. They are used for applications such as automotive exhaust systems where resistance to general corrosion is superior to carbon steels. However, there are not enough research for ferritic stainless steels on weldability mainly used as automotive exhaust manifolds. In this study, mechanical and microstructure properties of as-welded STS 429L and STS 444 ferrite stainless steels were confirmed by tensile, bending, hardness test, optical microscopy and scanning electron microscopy. Tensile strength of the STS 444 is higher than the STS 429L when it is a raw material. In contrast to this fact, STS 429L indicated higher tensile strength after butt welded. In addition, the hardness have a increasing tendency as getting down on the bead.

• Transactions of the Korean hydrogen and new energy society
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• v.24 no.4
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• pp.311-319
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• 2013

A clear understanding on cell voltage-reversal behavior due to local hydrogen starvation in a stack is of paramount importance to operate the fuel cell vehicle (FCV) stably since it affects significantly the cell performance and durability. In the present study, a novel experimental method to simulate the local cell voltage-reversal behavior caused by local hydrogen starvation, which typically occurs only one or several cells out of several hundred cells in a stack of FCV, has been proposed. Contrary to the conventional method of overall fuel starvation, the present method of local hydrogen starvation caused the local cell voltage-reversal behavior in a stack very well. Degradation of both membrane electrode assembly (i.e., pin-hole formation) and gas diffusion layer due to an excessive exothermic heat under voltage-reversal condition was also observed clearly.