• Journal of Welding and Joining
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• v.17 no.5
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• pp.29-35
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• 1999

• Journal of Hydrogen and New Energy
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• v.22 no.5
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• pp.592-598
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• 2011

Electrode of solid oxide fuel cell must have sufficient porosity to allow gas transport to the interface with electrolyte effectively but high porosity has a negative impact on structural stability in electrode support. Thus, the upper limit of porosity is based on consideration of mechanical strength of electrode. In this study, the effect of microstructure of Ni-YSZ anode supported SOFC on the mechanical and electrical property was investigated. LSCF composite cathode and 8YSZ electrolyte were used. The porosity of the anode was modified by the amount of graphite powder and added graphite contents were 24, 18, 12 vol%, respectively. The higher the porosity, the better the electrical performance, $P_{max}$. While the flexural strength decreased with increasing the amount of graphite. But the rate of increase in electrical performance and the rate of decrease in mechanical strength were not directly proportional to amount of graphite. The optimum graphite content incorporating both electrical and mechanical performance was 18 vol%.

• Journal of Korea Foundry Society
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• v.24 no.3
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• pp.165-174
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• 2004

The pore formation characteristic of Mg alloy during Lost Foam Casting(LFC) was investigated with reduced pressure test and real casting, which was compared with the results of previous work for Al alloy. Cast Mg alloys in LFC had much lower porosities in comparison with those of Al alloys. Also, the proper pouring temperature gave the minimum porosity like Al alloy although it was higher than that of Al alloys due to the worse fluidity of Mg alloy. The pore formation mechanism of Mg alloy in LFC was similar to that of AI alloy but the critical temperature showing the different mechanism is higher than that of Al alloy as much as $30{\sim}50^{\circ}C$. The result that Mg alloy in LFC had the lower porosity comparing with Al alloy was due to the extra solubility of hydrogen gas although the solubility of Al alloy was easily exceeded by the external sources like pyrolyzed polystyrene products. The mold evacuation gave the lower porosity due to the removal of polystyrene pyrolysis products, and reduced shrinkage defects. Also, there was a proper evacuation pressure that gave a porosity of almost 0vol%. But much higher vacuum degree than this proper pressure caused the severe entrapment of polymer pyrolysis products that gave the large porosity.

• Transactions of Materials Processing
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• v.28 no.1
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• pp.21-26
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• 2019

Direct Laser Melting (DLM) of $Ti-xTiH_2$ (mixing ratio x = 2, 5, 10 wt.%) blended powder is characterized by producing porous titanium parts. When a high energy laser is irradiated on a $Ti-TiH_2$ blended powder, hydrogen gas ($H_2$) is produced by the accompanying decomposition of the $TiH_2$ powder, and acts as a pore-forming and activator. The hydrogen gas trapped in a rapidly solidified molten pool, which generates porosity in the deposited layer. In this study, the effects of a $TiH_2$ mixing ratio and the associated processing parameters on the development of a porous titanium were investigated. It was determined that as the content of $TiH_2$ increases, the resulting porosity density also increases, due to the increase of $H_2$ produced by $TiH_2$. Also, porosity increases as the scan speed increases. As fast solidified melting pools do not provide enough time for $H_2$ to escape, the faster the scan speed, the more the resulting $H_2$ is captured by the process. The results of this study show that the mixing ratio (x) and laser machining parameters can be adjusted to actively generate and control the porosity of the DLM parts.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.4
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• pp.1460-1465
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• 2012

The semi-automatic gas metal arc welding equipment was developed and the weldability of zinc coated steel pipes was evaluated in terms of strength, porosity and welding parameters including shielding gas composition. The good bead appearance and the reduction of porosity in the welds could be possibly obtained by adding $O_2$ to Ar. The strength and joint efficiency of welds made by the semi-automatic welding equipment was about 1.8 times higher compared with welds manually made. The integrity of welds was confirmed by the water pressure test as well, Finally, it is expected that the weld productivity will be enhanced even unskilled welders can produce quality welds by operating the semi-automatic welding equipment.

• Laser Solutions
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• v.7 no.2
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• pp.19-26
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• 2004

The effect of shield gas on the weldability, mechanical properties and formability of CO2 laser weld joint in 600MPa grade high strength steel was investigated. Bead on plate welds were made under various welding speed and shield gas. Tensile test was carried out under the load of perpendicular and parallel direction to the weld line, Formability of the joint was evaluated by Erichsen test. As the welding speed increases, the porosity fraction decreases. The porosity fraction in the joint used Ar-$50\%He$ mixed gas as a shield gas was lower than that of the joint used Ar gas. Hardness at the weld metal of full penetrated joint was nearly equal to that of water quenched raw metal. In a tensile test under a perpendicular load to the weld axis, strength and elongation of joint produced by optimum condition were nearly equal to those of base metal. However, the strength of joint in a tensile test under a parallel load to weld axis was higher than that of raw metal, but the elongation of joint was lower than that of raw metal. Elongation and formability were further increased by the method of using Ar+He mixed gas as a shield gas as compared with Ar gas. Formabilities of joints were recorded ranging from $58\%\;to\;70\%$ of that of base metal with different shield gases.

• Journal of Powder Materials
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• v.22 no.1
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• pp.32-38
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• 2015

The effect of heat treatment environment on the microstructure and properties of tantalum coating layer manufactured by kinetic spraying was examined. Heat treatments are conducted for one hour at $800^{\circ}C$, $900^{\circ}C$, and $1000^{\circ}C$ in two different environments of vacuum and Ar gas. Evaluation of microstructure and physical properties are conducted. High density ${\alpha}$-tantalum single phase coating layer with a porosity of 0.04% and hardness of 550 Hv can be obtained. As heat treatment temperature increases, porosity identically decreases regardless of heat treatment environment (vacuum and Ar gas). Hardness of heat treated coating layer especially in Ar gas environment deceases from 550 Hv to 490 Hv with increasing heat treatment temperature. That in vacuum environment deceases from 550 Hv to 530 Hv. The boundary between particles became vague as heat treatment temperature increases. Oxygen distribution of tantalum coating layer is minute after heat treatment in vacuum environment than Ar gas environment.

• Journal of the Korean Institute of Gas
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• v.18 no.3
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• pp.20-30
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• 2014

To develop a unconventional gas reservoir, an analysis of tight rock property are required. Especially, conventional measurements are difficult to be applied to unconventional resources such as tight gas reservoir because the permeability are extremely low compared to a conventional gas reservoir. In this study, an apparatus was developed for measuring low permeability and porosity based on a pressure pulse decay method under unsteady state conditions. The apparatus was applied for measuring the porosity and permeability of tight sand core samples from Gyeongsang basin in Korea. As a validation of the measurement, regression analysis was carried out using the dimensionless pseudo-pressure between the measured data and analytical solution. The results show the correlation coefficients above 0.96. Therefore, it is believed that the apparatus has a high accuracy.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.2
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• pp.207-217
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• 2016

Permeability can not be expressed as a function of porosity alone, it depends on the porosity, pore size and distribution, and tortuosity of pore channels in concrete. There has been considerable interest in the relationship between microstructure and transport in cementitious materials, however, it is very rare to deal with the theoretical study on gas permeability coefficient in connection with carbonation of concrete and the effect of volumetric fraction of cement paste or aggregate on the permeability coefficient. The majority of these researches have not dealt with this issue combined with carbonation of concrete, although carbonation can significantly impact on the permeability coefficient of concrete. In this study, fundamental approach to compute gas permeability of (non)carbonated concrete is suggested. For several compositions of cement pastes, the gas permeability coefficient was calculated with the analytical formulation, followed by a microstructure-based model. For carbonated concrete, reduced porosity was calculated and this was used for calculating the gas permeability coefficeint. As the result of calculation of gas permeability for carbonated concrete, carbonation leaded to the significant reduction of gas permeability coefficient and this was obvious for concrete with high w/c ratio. Meanwhile, the relationship between gas permeability and water permeability has a linear function for cement paste based on Klinkenberg effect, however, which is not effective for concrete. For the evidence of the modeling, YOON's test was accomplished and these results were compared to each other.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.4
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• pp.374-380
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• 2015

In this paper, a dynamic model describing the 2 phase effect on the gas diffusion layer depending on load change of a fuel cell stack was developed to examine the effects of liquid water in fuel cell cathode gas diffusion layer on the fuel cell performance. For the developed model, 2 phase effect on the performance of a fuel cell stack depending on the load changes, concentration distribution of water vapor and oxygen inside a gas diffusion layer, the effect of the thickness and porosity of the gas diffusion layer on the fuel cell stack voltage were examined. As a result, a fuel cell stack voltage for the 2 phase model within the scope of the research become lower than that for the 1 phase model regardless of the load. Although oxygen molar concentration for the gas diffusion layer adjacent to the catalyst layer was the lowest, water vapor concentration is the highest. In addition, as thickness and porosity of the gas diffusion layer increased and decreased, respectively, the fuel cell stack voltage decreased.