• 연구논문집
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• s.31
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• pp.113-125
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• 2001

Silicon addition in titanium alloys generally results in solid solution hardening by silicon itself and precipitation hardening by titanium silicides. The morphology and distribution of the titanium silicides depend upon the alloy chemistry or the heat treatment condition, and play an important role in improving the mechanical properties of the alloys. In this study, the morphology and crystallographic characteristics of the titanium silicides in the Ti-Fe-Si alloy system were studied. Three types of silicides were found in the alloys; (1) interconnected chain-like silicides at grain boundary, (2) coarse silicides over im, (3) fine silicides smaller than 0.2m. Ti3Si was dominant in cast + HIP condition while Ti5Si3 was dominant in as-cast state. It is recognized that $Ti_5Si_3$$\rightarrow$$Ti_3Si$ transition occurred by the peritectoid reaction and it may be promoted by the pressure during HIP. However, in the case of the fine silicides, $Ti_3Si$ and $Ti_5Si_3$ were found simultaneously even after HIP. Such a fine silicide was found to have a crystallographic orientation relationship with matrix.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.119-119
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• 2010

We report strong exciton transition and exciton-phonon couplings in photoluminescence (PL) of ZnO thin films grown on MgO/sapphire (buffer/substrate) by plasma-assisted molecular beam epitaxy. The PL spectra at 10 K showed the intensity of the dominant emission, donor-bound exciton transition of front surface (top surface, the latter part in growth) is found to be about 100 times higher than that of back surface (in-depth bottom area, the initial part), while the room temperature PL spectra showed dominant contributions from the free exciton emissions and phonon-replicas of free excitons for front surface and back surface, respectively, It could be attributed to the strong contributions of exciton-phonon coupling. Time resolved PL spectra reveal that the life time of exciton recombination from the front surface are longer than those from back surface. This is most probably due to the fact that reduction of non-radiative recombination in the front surface. This investigation indicates that the existence of native defects or trap centers which can be reduced by the proper initial condition in growth and the exciton-phonon interaction couplings play an important role in optical properties and crystal quality of ZnO thin films.

• Journal of the Korean Society of Industry Convergence
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• v.24 no.3
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• pp.261-269
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• 2021

This study was evaluated the elastic wave properties according to tension of Incoloy 825 alloy with different solution treatment temperature and aging time. Solution treatment was carried out at 700, 800, 900, and 1000 ℃ for 1 hour, and aging was carried out at 700 ℃ for 1, 5, 10, and 30 hours. As the solution treatment temperature increased, the tensile strength decreased and the elongation increased. However, as the aging time increased, the tensile strength increased and the elongation decreased. The dominant frequency decreased as the solution treatment temperature increased, but increased as the aging time increased. The dominant frequency according to the solution treatment and aging time increased as the tensile strength increased, but increased despite the decrease in elongation.

• Corrosion Science and Technology
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• v.20 no.6
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• pp.325-334
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• 2021

In the open system (vessel and pipe), the maximum corrosion rate of carbon steel at ca. 80 ℃ was obtained due to the decrease of dissolved oxygen by increasing the solution temperature. Effect of temperature on the cavitation damage can be explained through several mechanisms. Moreover, when cavitation occurs on the surface of metal and alloys, whether cavitation is erosion or corrosion is still controversial. This work focused on the effect of solution temperature on the corrosion of carbon steel under cavitation in an open system, Tests were performed using an electrochemical cavitation corrosion tester in 3.5% NaCl solution and the effect of solution temperature of carbon steel was discussed. Cavitation corrosion rate can be increased by cavitation, but when the temperature increases, a dissolved oxygen content reduces at a very high speed and thus the maximum cavitation corrosion temperature changed from 80 ℃ to 45 ℃. Below the maximum cavitation temperature, the electrochemical effect was more dominant than the mechanical effect by increasing temperature, but over the maximum cavitation temperature, the mechanical effect was more dominant than the electrochemical effect by increasing temperature.

• Journal of the Korean Society of Visualization
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• v.20 no.3
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• pp.10-18
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• 2022

We present an experimental investigation on emulsions created during the impact process between a surfactant-laden droplet and an oil layer on water. By varying the surfactant concentration and the viscosity of oil layer, we created emulsions and visualized them using multi-dimensional high-speed imaging. Our analysis shows that the emulsions are more likely to be unstable and decay within a minute if the impacting droplet contains more surfactant. We also found that there are three mechanisms of generation of emulsions depending on the concentration of surfactant and the viscosity of oil layer; the jet pinch-off, cavity pinch-off, and tearing of oil layer. Jet and cavity pinch-off turned out to be dominant mechanisms for high oil viscosities, while tearing of oil layer is dominant for low oil viscosities. Our result is potentially useful in designing optimal dispersant properties for offshore oil contamination.

• Journal of Environmental Science International
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• v.32 no.5
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• pp.329-341
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• 2023

We surveyed the vegetation of an ecological landscape preservation area (legally protected conservation areas or national parks) and the surrounding areas of Mt. Cheonggye, Republic of Korea, to explore the conservation implications for preservation areas and surrounding transition areas. We calculated diversity indices to identify the properties of the preservation and surrounding areas that are relevant to conservation efforts. We then compared the plant community composition between the areas using field and quadrat surveys in the preservation and surrounding areas. The cover of the dominant species in all tree and herb layers was markedly higher in the preservation area than in the peripheral zones. The species richness indices were significantly higher in the preservation area than in the peripheral zones. Ordination using detrended canonical correspondence analyses showed that the cover of the dominant tree species and rocks could explain the distribution of plant species in the Cartesian space of the ordination. Our results demonstrate that physiognomically designated protected areas match well with ecological data based on diversity indices and ordination analyses and that disturbances in the areas surrounding the ecological landscape of preservation areas can have considerable impacts on plant diversity indices. Hence, the preservation and management of surrounding areas are essential conservation elements for protecting the entire ecological landscape of preservation areas.

• Korean Journal of Soil Science and Fertilizer
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• v.46 no.4
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• pp.281-287
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• 2013

Due to its high salt content and poor physical properties in reclaimed tidal lands, it is important to ameliorate soil physical properties to improve the efficiency of desalination. The objective of this study was to evaluate the changes of soil properties at Saemangeum reclaimed tidal saline soil with various soil amendments. Field experiment was conducted at Saemangeum reclaimed tidal land in Korea and the dominant soil series was Munpo series (coarse loamy, mixed, nonacid, Mesic, Typic, Fluvaquents). Woodchips, crushed-stone, oyster shell, coal bottom ash, and rice hull were added as soil amendments and mixed into surface soil to improve soil physical properties. There was large variability in soil hardness, but oyster shell treatment was significantly lower soil hardness at surface layer. Soil hardness was not significantly different below 15 cm depth. Infiltration rate was also significantly greater at oyster shell treatment. This may be due to the leaching of Ca ions from oyster shell and improved soil properties. However, there was no statistical significant difference of the soil bulk density, moisture content, and porosity. Improved physical properties increased desalinization rate in soil and retarded the resalinization rate when evapotranspiration rate was high. Although soil salinity was significantly decreased with oyster shell amendment, soil pH was increased that should be made up as a soil amendment. Our results indicated that oyster shell application increased infiltration rate and improved soil hardness, and thus oyster shell could be used to improve soil salinity level at Saemangeum reclaimed tidal saline soil.

• Journal of the Korean Society of Food Science and Nutrition
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• v.36 no.12
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• pp.1617-1621
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• 2007

The 21 Kimchi samples collected by a contest for the best Kimchi homemaker in Jeonju were analysed to find major microbial composition and the correlation between sensory scores and the microbial properties, which include total microbial numbers, dominant strain number, subdominant strain number, yeast strain numbers, and floral diversity. The most common microbial composition of the Kimchi samples was Leuconostoc mesenteroides as dominant strain, and Lactobacillus sakei as subdominant strain, the pattern of which was also observed in all three Kimchi samples with the highest sensory scores, but not in all three Kimchi samples with the lowest sensory scores. However none of the other examined properties showed any significant correlation to sensory scores. This result means that the taste of fermented Kimchi depends mainly on the composition of bacterial species and that of Leuconostoc mesenteroides as dominant strain and Lactobacillus sakei as subdominant strain is the best for good taste. Yeast strains were found in the range of $3.8{\sim}4.6log\;CFU/g$ from 8 Kimchi samples and all the strains were identified to be Saccharomyces servazzii. However, fungi were not detected from any of the Kimchi. samples.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.8
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• pp.666-670
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• 2007

Aluminuim doped zinc oxide(ZnO:AL)Films have been prepared on Polyimide(PI) and Coming 7059 glass substrates by r.f. magnetron sputtering method. The structural of the ZnO:Al films were studied in accordance with various deposition R.F power and working pressure by XRD, SEM. And The electrical and optical properties of ZnO:Al films were characterized by Hall effect and UN visible spectrophotometer measurements, ZnO:Al films had were hexagonal wurtzite structure and dominant c-axis orientation. The R.f power and working pressure for optimum condition to fabricate the transparent conductive films using a PI substrate were 2 mTorr and 100W, respectively. The resistivity of the ZnO:Al films prepared under this condition were $9.6{\times}10^{-4}{\Omega}cm$. The optical transmittance of 400nm thick films at 550nm is ${\sim}85 %$.

• Korean Journal of Materials Research
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• v.26 no.10
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• pp.542-548
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• 2016

The influence of NiCrAlY bond coating on the adhesion properties of an Fe thermal coating sprayed on an Al substrate was investigated. By applying a bond coat, an adhesion strength of 21MPa was obtained, which was higher than the 15.5MPa strength of the coating without the bond coat. Formation of cracks at the interface of the bond coat and the Al substrate was suppressed by applying the bond coat. Microstructural analysis of the coating interface using EBSD and TEM indicated that the dominant bonding mechanism was mechanical interlocking. Mechanical interlocking without crack defects in the coating interface may improve the adhesion strength of the coating. In conclusion, the use of an NiCrAlY bond coat is an effective method of improving the adhesion properties of thermal sprayed Fe coatings on Al substrates.