• Journal of Fashion Business
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• v.11 no.6
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• pp.52-61
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• 2007

To increase the ultraviolet radiation (UVR) protection of cotton fabric, ultraviolet protection (UVP) materials were treated onto cotton fabric using a new technique, UV-curing. A photocrosslinkablepolymer, poly(ethylene glycol) dimethacrylate was used as a UV-curable resin in the presence of a small amount of photoinitiator. Two kinds of UVP materials were used, UV-absorber, 2,2'-dihydroxy-4-methoxy benzophenone, and UV-scatterer, $TiO_2/ZnO$ Pad-dry-cure method in employing these materials onto cotton was also conducted to compare the effectiveness and the washfastness of UVP treatment between curing methods. UVP treated cotton fabric showed a moderate increase in UVP in case of 2,2'-dihydroxy-4-methoxy benzophenone treatment and a high increase in case of $TiO_2/ZnO$. UV-curing method increased the washfastness of UVP property of $TiO_2/ZnO$ treated cotton fabrics. However, in case of 2,2'-dihydroxy-4-methoxy benzophenone, similar wash fastnesses of UV-cured and pad-dry-cured cotton were observed. It can be presumed that 2,2'-dihydroxy-4-methoxy benzophenone was not significantly affected by water since its hydrophobicity. In short, UV-curing of UVP materials onto cotton was successfully done, and treated cotton fabrics showed the increased UVP properties and an increased washfastness in some extent.

• Korean Journal of Materials Research
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• v.16 no.1
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• pp.63-67
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• 2006

The characteristics of the wet-etching of ZnO thin films were investigated using hydrochloric and phosphoric acid solutions as etchants. The etch rate of ZnO films, using highly diluted hydrochloric acid solutions at a concentration of 0.25% in deionized water, was determined to be about 120 nm/min, and linearly increased with increasing the acid concentration, resulting in $1.17{\mu}m/min$ when a 2% HCl solution was used. The surface of ZnO etched by an HCl solution, observed by scanning electron microscopy, showed a rough morphology with a high density of hexagonal pyramids or cones with sidewall angles of about ${\sim}45^{\circ}C$. Moreover, the sidewall angles of the masked area were similar to those of the pyramids on the surface. In comparison, the surface of ZnO etched by a phosphoric acid had a smooth surface morphology. The origin of this difference is from the very initial stage of etching, indicating that the etch-mechanism is different for each solution. Furthermore, when $H_3PO_4$ was added to the HCl aqueous solution, the morphology of the etched surface was greatly enhanced and the sidewall angle was also increased to about $65^{\circ}C$.

• Korean Journal of Materials Research
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• v.25 no.4
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• pp.209-213
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• 2015

Synthesis of nano-silica using water glass in a Sol-Gel process is one of several methods to manufacture nano-silica. In nano-silica synthesized from water glass, there are various metal impurities. However, synthesis of nano-silica using water glass in a Sol-Gel process is an interesting method because it is relatively simple and cheap. In this study, nano-silica was synthesized from water glass; we investigated the effect of pH on the synthesis of nano-silica. The morphology of the nanosilica with pH 2 was flat, but the surface of the nano-silica with pH 10 had holes similar to small craters. As a result of ICP-OES analysis, the amount of Na in the nano-silica with pH 2 was found to be 170 mg/kg. On the other hand, the amount of Na in the nano-silica with pH 10 was found to be 56,930 mg/kg. After calcination, the crystal structure of the nano-silica with pH 2 was amorphous. The crystal structure of the nano-silica with pH 10 transformed from amorphous to tridymite. This is because elemental Na in the nano-silica had the effect of decreasing the phase transformation temperature.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.4
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• pp.364-369
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• 2005

An experimental study was conducted on the thermal conductivity of various grouting materials for geothermal heat exchanger which is used as a heat sink or source in the heat pump system. The grouting of the vertical heat exchanger is important for environmental and heat transfer reasons and is generally accomplished by the placement of a low permeability material into the annular space between the borehole wall and the pipes suspended in the borehole. In this study, a lab scale test apparatus was made and measured the thermal conductivity of four grouting materials. As a result, the temperature rising tendency was similar among them, but the increasing rate was different. Thus the thermal conductivity showed a maximum difference of $27\%$ among grouting materials.

• Corrosion Science and Technology
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• v.9 no.4
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• pp.164-170
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• 2010

Thermodynamic consideration was performed for Alloy 617 exposed to an impure helium ($H_2$ 20pa, $H_2O$ 0.5pa, $CH_4$ 2pa and CO 5pa) at $950^{\circ}C$. Oxidation power was decreased in the order Al > Ti > Si > Cr > Mn. Decarburization and carburization reactions were available leading to carbon activity decrease and increase, respectively, depending on carbon and Cr activities. The thermodynamic prediction was compared with the experimental results obtained in similar conditions (($H_2$ 20pa, $H_2O$ 0.05pa, $CH_4$ 5pa and CO 2pa) and $950^{\circ}C$) by others for Alloy 617. The driving force for oxidation of Al, Ti and Si is very large to be oxidized at a given impure helium and the environment is actually carburizing towards the structural alloy, which is consistent with this work.

• Journal of Powder Materials
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• v.25 no.5
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• pp.402-407
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• 2018

Molybdenum silicide has gained interest for high temperature structural applications. However, poor fracture toughness at room temperatures and low creep resistance at elevated temperatures have hindered its practical applications. This study uses a novel powder metallurgical approach applied to uniformly mixed molybdenum silicide-based composites with silicon carbide. The degree of powder mixing with different ball milling time is also demonstrated by Voronoi diagrams. Core-shell composite powder with Mo nanoparticles as the shell and ${\beta}-SiC$ as the core is prepared via chemical vapor transport. Using this prepared core-shell composite powder, the molybdenum silicide-based composites with uniformly dispersed ${\beta}-SiC$ are fabricated using pressureless sintering. The relative density of the specimens sintered at $1500^{\circ}C$ for 10 h is 97.1%, which is similar to pressure sintering owing to improved sinterability using Mo nanoparticles.

• Journal of Korea Foundry Society
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• v.32 no.6
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• pp.269-275
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• 2012

Al-Mg-Si/Al hybrid alloy was prepared by Duo-casting and the mechanical behavior was evaluated based on their microstructure and mechanical properties. The hybrid aluminum alloy included the Al-Mg-Si alloy with fine eutectic structure, pure Al with the columnar and equiaxed crystals, and the macro-interface existing between Al-Mg-Si alloy and pure Al. The growth of columnar grains in pure Al occurred from the macro-interface. The tensile strength, 0.2% proof stress and bending strength of the hybrid aluminum alloy were almost similar to those of pure Al, and the elongation was much higher than the Al-Mg-Si alloy. The fracture of the hybrid alloy took place in pure Al side, indicating that the macro-interface was well bonded and the mechanical behavior strongly depends on the limited deformation in pure Al side.

• Composites Research
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• v.14 no.6
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• pp.1-8
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• 2001

In this paper, the sandwich panel composites consisting of core material and face sheet were studied to evaluate the mechanical properties, noise level and fire resistance including flammability, smoke, and toxicity. Four types of sandwich panel were prepared using various kinds of panel and honeycomb materials. It was observed that Al honeycomb/Al skin composite materials had the excellent flatwise tensile strength and edgewise compressive strength compared with other types of composites. The flatwise compressive strength and flexural strength of Nomex honeycomb/Al skin composite were higher than those of other composites. PMI form/Al skin composite showed the higher core shear strength and facing bending strength. From the experimental results of flame resistance tests, it can be said that the phenol based skin composite has the excellent flame retardation properties, which are similar to those of the commercial skin composites.

• Journal of the Korea Concrete Institute
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• v.17 no.6 s.90
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• pp.1053-1064
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• 2005

The mechanical damage of concrete is normally attributed to the formation of microcracks and their propagation and coalescence into macroscopic cracks. This physical degradation is caused from progressive and hierarchical damage of the microstructure due to debonding and slip along bimaterial interfaces at the mesoscale. Their growth and coalescence leads to initiation of hairline discrete cracks at the mesoscale. Eventually, single or multiple major discrete cracks develop at the macroscale. In this paper, from this conceptual model of mechanical damage in concrete, the computational efforts were made in order to characterize physical cracks and how to quantify the damage of concrete materials within the laws of thermodynamics with the aid of interface element in traditional finite element methodology. One dimensional effective traction/jump constitutive interface law is introduced in order to accommodate the normal opening and tangential slips on the interfaces between different materials(adhesion) or similar materials(cohesion) in two and three dimensional problems. Mode I failure and mixed mode failure of various geometries and boundary conditions are discussed in the sense of crack propagation and their spent of fracture energy under monotonic displacement control.

• Journal of the Korean Ceramic Society
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• v.46 no.5
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• pp.452-455
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• 2009

A cost-effective route to synthesize $\beta$-SiAlONs from Si mixtures by reaction bonding followed by post-sintering was investigated. Three different z values, 0.45, 0.92 and 1.87, in $Si_{6-z}Al_zO_zN_{8-z}$ without excess liquid phase were selected to elucidate the mechanism of SiAlON formation and densification. For RBSN (reaction-bonded silicon nitride) specimens prior to post-sintering, nitridation rates of more than 90% were achieved by multistep heating to $1400^{\circ}C$ in flowing 5%$H_2$/95%$N_2$; residual Si was not detected by XRD analysis. An increase in density was acquired with increasing z values in post-sintered specimens, and this tendency was explained by the presence of higher amounts of transient liquid phase at larger z values. Measured z values from the synthesized $\beta$-SiAlONs were similar to the values calculated for the starting compositions. Slight deviations in z values between measurements and calculations were rationalized by a reasonable application of the characteristics of the nitriding and post-sintering processes.