• Polymer(Korea)
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• v.27 no.1
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• pp.46-51
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• 2003

In this work, the electrode far fuel cell was fabricated by mixing carbon blacks with activated carbon fibers (ACFs) in order to form the proper three phase distribution, and then the change of electrode in three phase distribution was investigated. Pt loading yield with ACF content and Pt particle size were determined by AAS and XRD measurements, respectively. And the pore structures, including specific surface area ($S_{BET}$), microporosity, and pore size distribution (PSD) for each electrode were systematically investigated by BET volumetric measurement. The morphology of electrode in three phase distribution was determined by SEM. As an experimental result, it was observed that Pt loading yield was not influenced on the content of ACF. While, the electrode in three phase distribution was largely improved in the case of 30% ACF addition on carbon blacks. These results were probably explained by the increase of the portion of micropores, resulting in increasing the active sites of catalyst.

• Journal of the Korean Institute of Gas
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• v.19 no.5
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• pp.41-46
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• 2015

It is known that in aluminum 6061-T6, which is composed of $Mg_2Si$ and ${\beta}-Al_5FeSi$, void nucleation grows around ${\beta}-Al_5FeSi$ of Al606-T6. In this work, growth of voids was checked by scanning a 6061-T6 specimen with SEM observation. The effects of dislocation damping, coherency strain and voids on ultrasonic attenuation and nonlinearity parameters were experimentally measured. It was observed that a nonlinearity parameter increases until 75 percent of fatigue life and decreases after that. From the results, the authors inferred that dislocation damping and coherency damping increase nonlinearity parameters and void nucleation decreases them as ultrasonic scattering increases with void. The application of nonlinearity parameters in estimating degradation of materials with complex microstructures through fatigue process, therefore, should be carefully considered.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.2
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• pp.77-81
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• 2019

Recently, as the problem of environmental pollution emerges, various methods of eco-friendly water treatment method are being developed. Polymer membranes, which are currently leading the market, are inexpensive, but have many problems in terms of chemical resistance and durability. Thus, ceramic membrane has been attracted great attention as high-efficiency water treatment due to excellent durability and chemical resistant. In this study, ceramic membranes were developed via pore structure, size control, and surface treatment. The pore size of the membrane was controlled through the formation of $ZrO_2$ and $TiO_2$ coating films. Tape casting and sol-gel process were used to form a ceramic coating film with nanopores on the surface of the membrane. Microstructure analysis of ceramic membrane and pore size analysis of the coating film were conducted and the change of water treatment characteristics was observed.

• Composites Research
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• v.34 no.1
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• pp.16-22
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• 2021

Polyurethane foam (PUF) can be manufactured in soft, semi-rigid, and hard forms, so it is used in various fields industrially. Among them, rigid PUF has excellent mechanical properties and low thermal conductivity, and is used as a thermal insulation material for buildings and as a cold insulation material in the natural gas transportation field. In this field, there is a steady demand on higher mechanical strength and lower thermal conductivity. In this study, a rigid PUF was manufactured, and the microstructure and physical properties were studied according to the impeller type (propeller, dispersed turbine) of the agitator. Through FE-SEM and Micro-CT analysis, it was confirmed that the average pore size of the foam manufactured with the dispersed turbine was 21.5% smaller than that of the pore made by the propeller. The compressive strength was improved by 15.4%, and the thermal conductivity decreased by 3.1% in the foam with small pores. This result can be utilized for fabricating PUF composites.

• Composites Research
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• v.20 no.4
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• pp.9-17
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• 2007

Powder metallurgy has been employed for the development of SiC particle reinforced aluminum metal matrix composites by means of hot isotropic pressing and vacuum hot pressing. A material model based on micro-mechanical approach then has been presented for the processes. Densification occurs by the inelastic flow of matrix materials during the consolidation, and consequently it depends on many process conditions such as applied pressure, temperature and volume fraction of reinforcement. The model is implemented into finite element software so that the process simulation can be performed enabling the predicted relative density to be compared with experimental data. In order to determine the performance of finished products, further tensile test has been conducted using the developed specimens. The effect of internal void of the materials on mechanical properties therefore can be investigated.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.18 no.6
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• pp.258-263
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• 2008

The fine aggregates of below 2 mm size was fabricated using by the vertical furnace in which the aggregates could be sintered at floating state and its physical properties were analyzed. The liquid formed at the surface of specimens sintered at $1200{\sim}l300^{\circ}C$ induced a gas in core to expand so the denser shell and porous core could be produced. The C series specimen fabricated by crushing an extruded body had an irregular shape and sharp edges but those became spheroidized by bloating due to gas expansion inside. The fine aggregates fabricated in this study was as light as floating in the water and had an apparent density of $0.68{\sim}1.08$. The absorption rate was proportioned to a porosity showing that the pores in core was not closed completely. The properties of fine aggregates fabricated in vertical furnace were similar with those of in an electric muffle furnace but the sticking-together phenomenon by surface fusion was not occurred in the vertical furnace. The aggregates fabricated in this study had a little lower impact resistance than that of natural aggregate but satisfied the unit volume weight standard specified in KS.

• Journal of the Korean Ceramic Society
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• v.39 no.10
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• pp.948-954
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• 2002

Porous reaction bonded SiC with high fracture strength was developed using Si melt infiltration method for use of the support layer in high temperature gas filter that is essential to develop the next generation power system such as integrated gasification combined cycle system. The porosity and pore size of porous RBSC developed in this study were in the range of 32∼36% and 37∼90 ${\mu}m$ respectively and the maximum fracture strength of porous RBSC fabricated was 120 MPa. The fracture strength and thermal shock resistance of porous RBSC fabricated by Si melt infiltration were much improved compared to those of commercially available porous clay bonded SiC due to the formation of the strong SiC/Si interface between SiC particles. The characteristics of pore structure of porous RBSC was varied depending on the amounts of residual Si as Well as the size of SiC particle used in green body.

• Applied Chemistry for Engineering
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• v.29 no.3
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• pp.318-324
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• 2018

In this study, PAN (polyacrylonitrile) based activated carbon fibers were prepared by water vapor activation method which is a physical activation method. Activation was performed with temperature and time as parameters. When the activation temperature reached 700, 750 and $800^{\circ}C$, the activation was carried out under the condition of a water vapor flow rate of 200 ml/min. In order to analyze the pore structure of activated carbon fibers, the specific surface area ($S_{BET}$) was measured by the adsorption/desorption isotherm of nitrogen gas and AFM analysis was performed for the surface analysis. Tensile tests were also conducted to investigate the effect of the pore structure on mechanical properties of fibers. As a result, the $S_{BET}$ of fibers after the activation showed a value of $448{\sim}902m^2/g$, the tensile strength decreased 58.16~84.92% and the tensile modulus decreased to 69.81~83.89%.

• Journal of the Korean Society for Nondestructive Testing
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• v.19 no.5
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• pp.333-339
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• 1999

It is well recognized that ultrasonic technique is one of the most common and reliable nondestructive evaluation techniques for quantitative estimation of defects in structures. For the quantitative and accurate estimation of internal defects. the characteristics of scattered ultrasonic wavefields must be understood. In this study. the scattered near-field and far-field due to a circular cavity embedded in infinite media subjected to incident SH-waves were calculated by the boundary element method. The frequency response of the scattered ultrasonic far-field was transformed into the time-domain signal by obtaining its inverse Fourier transform. It was found that the amplitude of time-domain signal decreases and its time delay increases as the distance between the detecting point of ultrasonic scattered field and the center of internal cavity increases.

• Korean Chemical Engineering Research
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• v.46 no.6
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• pp.1142-1147
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• 2008

Nano-structured porous carbon fiber(PCF) for the catalyst supports of the direct methanol fuel cell (DMFC) were prepared from the mesophase pitch by using the nano-MgO powders. Specific surface area of the PCFs was $8{\sim}58m^2/g$ and surface pore structures had almost meso pore diameter of 10~20 nm which were depending on the amount of MgO spheres. Aqueous reduction method was used to load 60 wt% PtRu on the prepared PCF supports. The electro-oxidation activity and single cell performance of the 60 wt% Pt-Ru catalysts were measured by cyclic voltammetry and unit cell test. The performances of these catalysts increased by 5~10% compared with one of commercial catalyst.