• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.6
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• pp.60-65
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• 2004

Numerical simulations and experiments have been carried out to investigate the effect of fuel injection nozzles on the combustion and NOx formation processes in a medium-speed marine diesel engine. Spray visualization experiment was performed in the constant-volume high-pressure chamber to verify the numerical results on the spray characteristics such as spray angle and spray tip penetration. Time-resolved spray behaviors were captured by high-speed digital camera and analyzed to extract the information on the spray parameters. Spray and combustion phenomena were examined numerically using FIRE code. Wave breakup and Zeldovich models were adopted to describe the atomization characteristics and NOx formation processes. Numerical results were verified with experimental data such as cylinder pressure, heat release rate and NOx emission. Finally, the effects of fuel injection nozzles on the engine performance were investigated numerically to find the optimum nozzle parameters such as fuel injection angle, nozzle hole diameter and number of nozzle holes. From this study, the optimum fuel injection nozzle (nozzle hole diameter, 0.32 mm, number of nozzle holes, 8 and fuel injection angle, $148^{\circ}$) was selected to reduce both the fuel consumption and NOx emission. The reason for this selection could be explained from the highest fuel-air mixing in the early phase of injection due to the longest spray tip penetration and the highest heat release rate after $19^{\circ}$ ATDC due to the increased injection duration.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.120-120
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• 2016

Ti-6Al-4V alloy have been used for dental implant because of its excellent biocompatibility, corrosion resistance, and mechanical properties. However, the integration of such implant in bone was not in good condition to achieve improved osseointergraiton. For solving this problem, calcium phosphate (CaP) has been applied as coating materials on Ti alloy implants for hard tissue applications because its chemical similarity to the inorganic component of human bone, capability of conducting bone formation and strong affinity to the surrounding bone tissue. Various metallic elements, such as strontium (Sr), magnesium (Mg), zinc (Zn), sodium (Na), silicon (Si), silver (Ag), and yttrium (Y) are known to play an important role in the bone formation and also affect bone mineral characteristics, such as crystallinity, degradation behavior, and mechanical properties. Especially, Zn is essential for the growth of the human and Zn coating has a major impact on the improvement of corrosion resistance. Plasma electrolytic oxidation (PEO) is a promising technology to produce porous and firmly adherent inorganic Zn containing $TiO_2(Zn-TiO_2)$coatings on Ti surface, and the a mount of Zn introduced in to the coatings can be optimized by altering the electrolyte composition. In this study, corrosion behavior of Ti-6Al-4V alloy after plasma electrolytic oxidation in solutions containing Ca, P and Zn were studied by scanning electron microscopy (SEM), AC impedance, and potentiodynamic polarization test. A series of $Zn-TiO_2$ coatings are produced on Ti dental implant using PEO, with the substitution degree, respectively, at 0, 5, 10 and 20%. The potentiodynamic polarization and AC impedance tests for corrosion behaviors were carried out in 0.9% NaCl solution at similar body temperature using a potentiostat with a scan rate of 1.67mV/s and potential range from -1500mV to +2000mV. Also, AC impedance was performed at frequencies ranging from 10MHz to 100kHz for corrosion resistance.

• Journal of the Korean Ceramic Society
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• v.38 no.5
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• pp.405-411
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• 2001

Compacts of a mixture of fine $\alpha$-Si$_3$N$_4$powders, 6% $Y_2$O$_3$and 1% $Al_2$O$_3$were attrition milled time on phase and microstructural development in silicon nitride ceramics. The sintered surface and the interior showed different behaviors in phase and microstructral developments. Increased oxygen content with increased milling time of powder mixture leads to the formation of Si$_2$$N_2$O phase at temperatures as low as 155$0^{\circ}C$. Si$_2$$N_2$O is stable in the interior of the samples but unstable in the surface region of the specimen sintered at higher temperature. This results in a duplex structure where the interior consists of Si$_2$$N_2$O grains dispersed in $\beta$-Si$_3$N$_4$matrix and a surface which contains only $\beta$-Si$_3$N$_4$. The alpha to beta phase transformation and the microstructural development are shown to be influenced by the formation and decomposition of the Si$_2$$N_2$O.

• Elastomers and Composites
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• v.39 no.2
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• pp.142-152
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• 2004

Tensile tests of two types of injection-molded polystyrene(PS) samples have been carried out over a wide range of temperature and strain rates in order to characterize their crazing behaviors. Mechanical properties were affected by the formation of crazes as well as test variables. Below the brittle-ductile transition temperature, the tensile stress and the ultimate elongation increased with the molecular weight, strain rate, and with decreasing temperature while the number and average length of crazes also increase. The crazing stress increased with molecular weight, strain rate, and with decreasing temperature. However, the dependence was small compared to the tensile stress. The gap between crazing stress and tensile stress which represents time fur craze formation and growth increased with molecular weight, strain rate, and with decreasing temperature. Crazing was activated near the ${\beta}$-relaxation temperature; crazing stress abruptly decreased at this temperature. During the tensile test, the craze density changed exponentially with the applied stress. At the initial stage, crazes formed slowly. Once a certain number of craze formed, however, the craze density increased rapidly. Craze nucleation and growth occur simultaneously.

• Journal of the Korean Chemical Society
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• v.37 no.4
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• pp.390-395
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• 1993

The x values and electrical conductivities of the nonstoichiometric compounds$ CeO_{2-x} have been measured in a temperature range from 600 to 1200$^{\circ}C$ under oxygen partial pressure of $2{\times}10^{-1}{\sim}1{\times}10^{-4}$ atm. The enthalpy of the defect formation shows an endothermic process with the oxygen partial pressure dependence (1/n value) of -1/3.18 ∼ -1/3.69. The activation energy and 1/n value for the electrical conductivity are estimated as 1.75 eV and -1/4, respectively. According to the x values, the $\sigma$ values, and the thermodynamic data, the defect structure of the ceria seems to be the formation of singly charged negative oxygen vacancies. The n-type semiconducting behaviors could be explained by the presence of excess metals in the lattice as the conduction electron donor.

• Journal of the Mineralogical Society of Korea
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• v.6 no.1
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• pp.38-47
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• 1993

Clinoptilolite and mordenite are important constituents of the Nuldaeri Trachytic Tuff and Guryongpo Dacitic Tuff of the Tertiary Janggi Group which were deposited in a lacustrine environment. The diagenetic cystallization sequences of zeolites in different tuffaceous sediments and their chemical behaviors have been studied to know the process of their formation. The paragenetic sequence established from textural observations and chemical data : Ca-smectite ${\leftrightarrow}$(Ca, K)-clinoptilolite${\leftrightarrow}$(K, Na)-mordenite, indicates that the chemical activities of alkalic ions and Si/Al activity ratio in pore fluids changed systematically with diagenetic alteration. The chemical trend of zeolite formation is characterized by decreasing Ca and Mg, non-variable Na and increasing K in the Nuldaeri Trachytic Tuff and by decreasing Ca and Mg, non-variable Na and increasing-decreasing K in the Guryongpo Dacitic Tuff. The paragenesis from glass via smectite to alkali zeolites indicates a sequence of incongruent dissolution reactions and subsequent crystallization. Inhomogeneity in chemical composition of each zeolite may be attributed to such processes.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.05a
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• pp.167-168
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• 2012

Films of CrN, $Cr_{40}Zr_9N$, and $Cr_{31}Zr_{16}N$ were deposited on a steel substrate by closed field unbalanced magnetron sputtering, and their oxidation behaviors at $700^{\circ}C$ and $800^{\circ}C$ for up to 60h in air were investigated. All the deposited films were composed of the CrN phase. Zirconium atoms in $Cr_{40}Zr_9N$ and $Cr_{31}Zr_{16}N$ films partially dissolved in the CrN phase. They advantageously refined the columnar structure, reduced the surface roughness, and increased the microhardness. The CrN film displayed relatively good oxidation resistance, owing to the formation of the highly protective $Cr_2O_3$ on its surface. The $Cr_{40}Zr_9N$ and $Cr_{31}Zr_{16}N$ films oxidized to $Cr_2O_3$ as the major phase and ${\alpha}-ZrO_2$ as the minor one. They oxidized primarily by the inward transport of oxygen. The addition of Zr could not increase the oxidation resistance of the CrN film, because the formed $ZrO_2$ that was intermixed in the $Cr_2O_3$-rich oxide layer was oxygen permeable, and developed the compressive stress in the oxide scale owing to the volume expansion during its formation.

• Bulletin of the Korean Chemical Society
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• v.11 no.6
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• pp.521-527
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• 1990

The binding characteristics and analytical applications of anilinium ion complexes with 18-crown-6 were studied by polarography and NMR. First, the electrochemical reduction of the 10 species of mono and dimethylsubstituted anilinium ion complexes with 18-crown-6 as host in methanol are examined. The addition of 18-crown-6 to anilinium guest solution the polarographic waves remain well defined but shifted toward more negative potentials, indicating the complex formation. The values of formation constants, log Κ for 10 species of methylsubstituted anilinium ion complexes with 18-crown-6 varies from 2.7 to 4.8 in methanol at $25^{\circ}C$. The stability order of complexes for 18-crown-6 is anilinilum > 4-methyl > 3,4-dimethyl > 3-methyl > 3,5-dimethyl > 2,4-dimethyl > 2,5-dimethyl > 2,3-dimethyl > 2-methyl > 2,6-dimethylanilinium ion. The steric hindrance shows significant effect. Second, Proton NMR was used to elucidate their interaction characteristics. From the results of so called NMR titration techniques, the behaviors of binding sites on complexation, and the stoichiometry and stability order of complex were obtained. And the later results show the satisfactory agreement with the quantitative values obtained by polarography. Finally, the individual determinations of anilinium ion mixtures were also accomplished by addition of 18-crown-6. In some mixtures of methyl or dimethylanilinium ions the reduction peaks of differential pulse method appeared into one unresolved wave attributed to the small difference of half-wave potential, ${\Delta}E_{1/2}$. In the presence of 18-crown-6, the polarographic waves were resolved into individual maxima because of the shift toward more negative direction by the difference of selectivity of anilinium ions with 18-crown-6. It may be concluded that quantitative analysis of methylanilinium ion mixture make possible because the half-wave potential shift by the selectivity difference due to the steric hindrance between methyl group and 18-crown-6 on complexation.

• Corrosion Science and Technology
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• v.20 no.6
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• pp.373-383
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• 2021

The effect of Cr addition to high Mn steel on flow-accelerated corrosion (FAC) behavior in a neutral aqueous environment was evaluated. For comparison, two types of conventional ferritic steels (API X70 steel and 9% Ni steel) were used. A range of experiments (electrochemical polarization and impedance tests, weight loss measurement, and metallographic observation of corrosion scale) were conducted. This study showed that high Mn steel with 3% Cr exhibited the highest resistance to FAC presumably due to the formation of a bi-layer scale structure composed of an inner Cr enriched Fe oxide and an outer Mn substituted partially with Fe oxide on the surface. Although the high Mn steels had the lowest corrosion resistance at the initial corrosion stage due to rapid dissolution kinetics of Mn elements on their surface, the kinetics of inner scale (i.e. Cr enriched Fe oxide) formation on Cr-bearing high Mn steel was faster in dynamic flowing condition compared to stagnant condition. On the other hand, the corrosion scales formed on API X70 and 9% Ni steels did not provide sufficient anti-corrosion function during the prolonged exposure to dynamic flowing conditions.

• Journal of The Korean Association of Information Education
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• v.19 no.3
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• pp.299-310
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• 2015

This study was conducted with the goal to identify the degree to which elementary school students' knowledge about personal information protection practices impacted their actual behavior with regard to privacy protection. To fulfill this goal, knowledge about personal information protection was set as (1) knowledge about concepts of personal information, (2) knowledge of the rights of information holders, (3) knowledge about the code of conduct for information protection, and (4) awareness of the value of personal information. As for students' behaviors to ensure their personal information protection those were set as their habits to comply with the personal in-formation protection code of conduct and their efforts to respond and recover from any personal information violation. This study was conducted targeting 510 elementary students. The degree of the students' knowledge and their behaviors was measured by first distributing a self-report survey to the students and then analyzing their responses. The results of the analysis revealed the following: First, it was found that there are no differences among the four factors of knowledge and behavior according to the status of their education. Second, the two factors that primarily affected their personal information protection behavior were found to be their awareness of the information protection code of conduct and awareness of the value of personal information. This study holds significance in that it makes suggestions as to how personal protection practices should be taught to public school students.