• Corrosion Science and Technology
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• v.5 no.2
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• pp.52-61
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• 2006

Recently, much of the current development in surface modification engineering are focused on multilayered coatings. Multilayered coatings have the potential to improve the tribological properties. Four different multilayered coatings were deposited on AISI D2 steel. The prepared samples are designed as $WC-Ti_{0.6}Al_{0.4}N$, $WC-Ti_{0.53}Al_{0.47}N$, $WC-Ti_{0.5}Al_{0.5}N$ and $WC-Ti_{0.43}Al_{0.57}N$. The multilayered coatings were investigated with respect to coating surface and cross-sectional morphology, roughness, adhesion, hardness, porosity and tribological behavior. Especially, wear tests of four multilayered coatings were performed by using a ball-on-disc configuration with a linear sliding speed of 0.017 m/sec, 5.38 N load. The tests were carried out at room temperature in air by employing AISI 52100 steel ball ($H_R=66$) having a diameter of 10 mm. The surface morphology, and topography of the wear scars of samples and balls have been determined by using scanning electron spectroscopy (SEM). Results have showed an improved wear resistance of the $WC-Ti_{1-x}Al_xN$ coatings with increasing of Al concentration. $WC-Ti_{0.43}Al_{0.57}N$ coating with the lower surface roughness and porosity with good adhesion enhanced wear resistance.

• Journal of the Korean Ceramic Society
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• v.50 no.5
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• pp.341-347
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• 2013

Kaolin-based membranes with a pore size of 0.30-0.40 ${\mu}m$ were successfully prepared by a simple pressing route using low-cost starting materials, kaolin and sodium borate. The prepared green bodies were sintered at different temperatures ranging between 900 and $1200^{\circ}C$. The sintered membranes were characterized by X-ray diffraction, mercury porosimetry, scanning electron microscopy, and capillary flowmetry. It was observed that the porosity decreased with an increase in both the sintering temperature and the sodium borate content, whereas the flexural strength increased with an increase in both the sintering temperature and the sodium borate content. The air flow rate decreased with an increase in the sodium borate content. The typical porosity, flexural strength, and specific flow rate of the kaolin-based membrane sintered with 5 wt% sodium borate at $1100^{\circ}C$ were 37%, 19 MPa, and $1{\times}10^{-3}L/min/cm^2$, respectively, at a p of 30 psi.

• Journal of the Korean Ceramic Society
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• v.52 no.3
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• pp.180-185
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• 2015

Low-cost ceramic membrane supports with pore sizes in the range of $0.52-0.62{\mu}m$ were successfully prepared by uniaxial dry compaction method using inexpensive raw materials including kaolin, bentonite, talc, sodium borate, and alkaline-earth oxides in carbonate forms (e.g., $MgCO_3$, $CaCO_3$, and $SrCO_3$). The prepared green supports were sintered at $1000^{\circ}C$ for 8 hr in air. The effect of alkaline-earth oxide additives on the flexural strength of clay-based membrane supports was investigated. The porosity of the clay-based membrane supports was found to be in the range of 33-34%. The flexural strength of the clay-based membrane supports with 1% alkaline-earth carbonates was found to be in the range of 42.8-52.7 MPa. The addition of alkaline-earth carbonates to clay-based membrane supports resulted in large increases (47-80%) in the flexural strength of the membrane supports, compared to that of membrane supports without alkaline-earth carbonates. The typical flexural strength of the clay-based membrane support with 1% $SrCO_3$ was 52.7 MPa at 33.8% porosity.

• Geomechanics and Engineering
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• v.11 no.6
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• pp.771-785
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• 2016

The thermal conductivity of soils is an important property in energy-related geotechnical structures, such as underground heat pumps and underground electric power cable tunnels. This study explores the effects of geotechnical engineering properties on the thermal conductivity of soils. The thermal conductivities of quartz sands and Korean weathered silty sands were documented via a series of laboratory experiments, and its variations with effective stress, porosity, and water saturation were examined. While thermal conductivity was found to increase with an increase in the effective stress and water saturation and with a decrease in porosity, replacing air by water in pores the most predominantly enhanced the thermal conductivity by almost one order of magnitude. In addition, we have suggested an improved model for thermal conductivity prediction, based on water saturation, dry thermal conductivity, saturated thermal conductivity, and a fitting parameter that represents the curvature of the thermal conductivity-water saturation relation.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.700-703
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• 2000

With respect to durability, the impotance of carbonation lies in the fact that it reduces the pH on the pore water in hardened concrete. However, the carbonation velocity is effected by the water/cement ratio, materials, unit cement weight, porosity, kinds of finishing materials, accuracy of constructing, environmental factors and so on. And the air permeability is closely related to the carbonation velocity because it represents the properties of concrete. This paper presents an experimental investigation on the carbonation effected by air permeability n mortar and concrete. As a result, it was found that the carbonation velocity of concrete is faster than that of mortar and it is possible to predict the carbonation velocity using air permeability.

• Journal of the Korean Ceramic Society
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• v.28 no.11
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• pp.917-925
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• 1991

For the present experiment five Portland cement mortars are in order: mortars with two different water/ cement ratios (W/C=0.45 and 0.50, each having no chemical additive), and those with an additive such as superplasticizer, air-entraining agent or water-repelling agent. We fix the W/C ratio of mortars having additive so that their pastes can yield the same workability as that of the cement mortar of W/C=0.50 with no additive. It is shown that the freeze-thaw resistivity depends heavily on the characteristic of wide pores. Despite a good deal of wide pores, the air-entrained specimen shows a good freeze-thaw resistivity due to appropriate air-pores. And also the specimen with water-repelling agent, which proves to cause the microstructure to become hydrophobic, make good resistance to freeze-thaw cycles in spite of its high wide-porosity. Our suggestion is that the freeze-thaw durability of Portland cement mortar/concrete can be more effectively enhanced by using air-entraining agent or water-repelling agent, and simutaneously by taking proper measures against foaming and/or the increased tendency of wide-pore building due to additive.

• Proceedings of the KIEE Conference
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• 2005.07b
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• pp.1717-1718
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• 2005

Zn/Air 전지는 방전하는 동안에 최종 방전 cut-off 전압에 이르기까지 평탄한 voltage profile의 전기화학적 특성을 보여준다. Air cathode 전극의 경우, 전극의 porosity에 따라 특성변화에 큰 영향을 가지는 것으로 보이며 이의 비교연구를 위해 사용되어지는 활성탄의 종류를 달리함으로써 이러한 인자의 영향을 이해하고자 하였다. 이러한 인자연구는 discharge voltage, specific capacity, 및 energy 등의 연구결과를 바탕으로 고찰되어졌으며 결과적으로 공기 유로를 통한 산소의 원활한 공급 여부가 주요 원인인 것으로 여겨진다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.114-117
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• 2006

The air filter in engine intake system has a function of filtrating the dirt in the scavenging air as well as attenuating the noise. The noise attenuation within the air cleaner filter, however, has been regarded as negligible by the field engineers. In this paper, for the analysis of the acoustical performance of air filter, an acoustical model was suggested and the characteristics of air filter system were investigated. Fibrous structure of the filter element was modeled as a micro-perforated panel using the flow resistivity and porosity. The pleated geometry of the filter element was modeled as two coupled ducts that have permeable walls, in which each duct area was assumed being constant. Using such simplified geometry, a mathematical model was developed for the sound propagation within a narrow duct system. Visco-thermal effect was considered in modeling the sound propagation through such tubes; the filter box was modeled as a rigid rectangular box. By combining two models, a four-pole transfer matrix was derived. For the validation purpose, transmission loss was measured for a plastic rectangular box containing an air filter. A noticeable effect of the air filter element was observed by including the filter into the box. Comparing the predicted and measured data, we found that the predicted TL agrees well with experimental results, in particular, in magnitude and frequency at TL troughs.

• Journal of the korean Society of Automotive Engineers
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• v.4 no.3
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• pp.40-47
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• 1982

Heat transfer on packed bed is considered to be important for the effective designs of chemical reaction equipment, air conditioning system, and storage type heat exchanger, etc. Currently studies are being carried out quite actively in this field in order to increase the heat transfer efficiency. The effect of heat transfer is closely relater to materials, shapes, porosities and packing states of packed bed as well as mutual dimensional relations between particles and the container. Investigation shows that heat transfer results appear to be influenced by such parameters as fluid velocity through packed bed, mass flow, and thermal properties. It is noted that viscosity is also considered to be an important factor in this problem. In this study, effective thermal conductivities on packed bed, effects of thermal conductivity (Ke) and friction factor (Fk) according to change of porosity(.epsilon.) and Reynolds number(Reh(, and pressure loss of the fluid, are experimentally investigated. Results show that the effective thermal conductivity increases and the friction factor decreased, as against the increase of Reynolds number. But as the increase of porosity increase them both.

• The Korean Journal of Ceramics
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• v.1 no.3
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• pp.147-151
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• 1995

Porous composite of $Al_2O_3$ and AIN based mullite and SiC can be prepared by alumium reaction synthesis and atmosphere controllied sintering in order to improve the durability of a gas filter body. The porous $Al_2O_3$-AIN-mullite, which has a strength of 168 kg/$\textrm{cm}^2$ and porosity of 51.59%, could be obtained by stmospheric firing at $1600^{\circ}C$ and the porous $Al_2O_3$-AIN-SiC with a porosity of 33% and strength of 977 kg/$\textrm{cm}^2$, could also be prepared. The average pore size has been changed from 0.2$\mu\textrm{m}$ in a reduction atmosphere and to 2$\mu\textrm{m}$ in an air atmosphere, respectively.