• The Transactions of the Korean Institute of Power Electronics
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• v.10 no.3
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• pp.296-301
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• 2005

This paper proposing the use of the Instantaneous reactive power method as a harmonic detection method for a single phase active filter system. This method is to detect harmonic components through d-q frame approach. The conventional use of d-q frame approach for a 3-phase system Is extended to the single phase system. The proposed system uses a multi-level inverter for harmonic compensation and the inverter is connected to the input side without using transformers. The proposed algorithm is verified by simulation and experiment.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.3
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• pp.171-177
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• 2005

Phase-shifting method using Fourier transform (PSM/FT) has been applied to measurement of in-plane displacement of a specimen. Thirty-two interference fringe patterns each of which has different phase of ${\pi}/16$ radian have been gathered from a specimen with in-plane displacement. Low-pass filtering by 2-D Fourier transform is used to suppress spatial noise of the fringe patterns. ${\alpha}-directional$ Fourier transform for PSM/FT is performed by use of the low-pass filtered 32 fringe patterns. Two kinds of specimens are used for experiment. One is a rectangular steel plate and the other one is a rectangular steel plate containing a circular hole at the center. In-plane displacement of each specimen is measured by PSM/FT, and calculated by finite element method (ANSYS) for comparison. The results are quite comparable, so that PSM/FT can be applied to measurement of in-plane displacement.

• Journal of Korea Foundry Society
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• v.36 no.4
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• pp.117-125
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• 2016

The effects of the Zn content on the microstructure and corrosion behavior in 1M NaCl solution were investigated in Mg-(0~6)%Zn casting alloys. The MgZn phase was scarcely observed in the Mg-1%Zn alloy, while the Mg-(2~6)%Zn alloy consisted of ${\alpha}$-(Mg) and MgZn phases. With an increase in the Zn content, the amount of the MgZn phase was gradually increased. Immersion and electrochemical corrosion tests indicated that the Mg-1%Zn alloy had the lowest corrosion rate among the alloys, and a further increase in the Zn content resulted in the deterioration of the corrosion resistance. Microstructural examinations of the corroded surfaces and EIS analyses of surface corrosion films revealed that the best corrosion resistance at 1%Zn was associated with the absence of MgZn phase particles in the microstructure and the contribution of Zn element to the formation of a protective film on the surface. A micro-galvanic effect by the MgZn particles led to the increased rate of corrosion at a higher Zn content.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.354-357
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• 2005

When Ti-6Al-4V is used in long steam turbine blades, the main issues are how to improve the fatigue strength as a problem of internal quality and how to forge the thinnest possible blades as problem of dimensional precision. To assure an excellent fatigue strength, it is important to make the two phase fine and equiaxial structure by providing enough plastic deformation in the two phase$(\alpha\;phase/\beta\;phase)$ temperature region. Accordingly, it needs to predict that forging temperature, preform design and forging velocity in forging process. To achieve this end, the two steps forging process was suggested to forge the thin and twisted blades with a precision hammer considering die forces and metal flow. Two steps forging process consists of the flattening forging process and finishing forging process. Process in forging of a 1016mm long steam turbine blade is designed by the finite element method. This study attempts to derive systematic design procedures for process design in the forging. Forging parameters was analyzed in two-dimensional plane-strain simulation and two steps forging process carried out in three-dimensional simulation. Consequently, optimal forging process parameters of long steam turbine blades in Ti-6Al-4V with a high dimensional precision are selected in the hammer die forging.

• Journal of the Korean Society for Heat Treatment
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• v.24 no.5
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• pp.262-270
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• 2011

Carbide precipitation and dissolution behavior at various temperatures during heat treatment has been studied in STD11 cold working die steel through confocal scanning laser microscopy; dilatometry; and X-ray diffraction analysis. The equilibrium phase diagram and phase fractions with temperature were calculated using a FactSage program. Confocal laser microscopic observation revealed that ${\alpha}$ to ${\gamma}$ transformation temperature is near $800^{\circ}C$; M7C3 carbides melt at $1245^{\circ}C$; and the melting temperature of STD11 is near $1370^{\circ}C$. XRD results indicated that the M23C6 carbides dissolve in the matrix if austenitized at over $1030^{\circ}C$; while the M7C3 carbides remain up to $1200^{\circ}C$ although their amount decreases. The calculated equilibrium phase diagram showed good agreement with experimental results on carbide dissolution and phase transformation temperatures.

• Journal of the Korean Ceramic Society
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• v.39 no.12
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• pp.1119-1123
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• 2002

Nanostructured spinel NiZn ferrites were prepared by the sol-gel method from metal nitrate raw materials. Analyses by X-ray diffraction and scanning electron microscopy showed the average particle size of NiZn ferrite was under 50 nm. The single phase of NiZn ferrites was obtained by firing at 250${\circ}C$, resulting in nanoparticles exhibiting normal ferrimagnetic behavior. The nanostructured $Ni_{1-X}Zn_XFe_2O_4$ (x=0.0∼1.0) were found to have the cubic spinel structure of which the lattice constants ${\alpha}_2$ increases linearly from 8.339 to 8.427 ${\AA}$ with increasing Zn content x, following Vegard's law, approximately. The saturation magnetization $M_s$ was 48 emu/g for x=0.4 and decreased to 8.0 emu/g for higher Zn contents suggesting the typical ferrimagnetism in mixed spinel ferrites. Pure NiZn ferrite phase substituted by Cu was observed before using the additive but hematite phase was partially appeared at $Ni_{0.2}Zn_{0.2}Cu_{0.6}Fe_2O_4$. On the other hand, the hematite phase in this NiZn Cu ferrite was disappeared after using the additive of acethyl aceton with small amount. The saturation magnetization Ms of $Ni_{0.2}Zn_{0.8-y}Cu_yFe_2O_4$(y=0.2∼0.6) as measured was about 51 emu/g at 77K and 19 emu/g at room temperature, respectively.

• Journal of Surface Science and Engineering
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• v.36 no.2
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• pp.200-205
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• 2003

Thermoelectric p-type $Fe_{0.98}$ $Mn_{ 0.02}$$Si_2$ bulk specimens have been produced by mechanical alloying and consolidation by vacuum hot pressing. The subsequent isothermal annealing was not able to fully transform the mestastable as -milled powders into the $\beta$ $-FeSi_2$ phase, so that the obtained matrix consisted of not only thermoelectric semiconducting $\beta$-FeSi$_2$ but also some residual, untransformed metallic $\alpha$ $- Fe_2$$Si_{ 5}$ and $\varepsilon$-FeSi mixtures. Interestingly, $\beta$ - $FeSi_2$ was more easily obtained in the low density specimen when compared to the high density specimen. The oxidation at 700 and $800^{\circ}C$ in air led to the phase transformation of the above described iron - silicides and the formation of a thin silica surface layer.

• Journal of the Korean Ceramic Society
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• v.37 no.3
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• pp.247-255
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• 2000

Silicon carbide with sialon was prepared by hot pressing and transient liquid-phase sintering, and the effects of sintering atmosphere and starting phases on their microstructural characteristics were investigated. The sintered SiC with Sialon composition(Y2O3, AlN, Si3N4) in argon atmosphere had high sintered density and large aspect ratio. But sintered specimens in nitrogen atmosphere showed low aspect ratio and small grian size, becuase of the retardation of phase transformation and grain growth. Addition of Y-Sialon powder to SiC also retarded the phase transformation to ${\alpha}$-SiC from ${\beta}$-SiC and densification. The SiC specimen prepared from the starting ${\beta}$-SiC powder with Sialon composition(Y2O3, AlN, Si3N4) showed the highest fracture toughness about 6.0 MPa$.$m1/2.

• Bulletin of the Korean Chemical Society
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• v.27 no.11
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• pp.1775-1779
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• 2006

A liquid chromatographic chiral stationary phase (CSP) based on (+)-(18-crown-6)-2,3,11,12-tetracarboxilic acid without extra free aminopropyl groups on silica surface has been demonstrated to be quite effective for the resolution of various $\beta$-amino acids. The retention factors ($k_1$) for the resolution of $\beta$-amino acids on the CSP were quite large and the large retention factors might be quite attractive along with the reasonable separation factors ($\alpha$) for preparative scale enantioselective chromatography. The large retention factors on the CSP were found to be reduced effectively by adding ammonium ion to mobile phase without sacrificing the chiral recognition efficiency of the CSP. Consequently, the CSP is also quite applicable for use in analytical enantioselective chromatography.

• Journal of Hydrogen and New Energy
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• v.14 no.2
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• pp.97-104
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• 2003

The structural transitions of the matrix and the second phases of $Ti_{1.0}Mn_{0.9}V_{1.1}$ and $Ti_{1.0}Cr_{1.5}V_{1.7}$ alloys upon hydrogenation have been investigated at 293K. The effect of hydrogen isotope on their crystal structures has been also discussed. The crystal structures, Phase abundance and lattice parameters of the hydrides were determined by the Rietveld method using X-ray diffraction data. At the experimental temperature, the $Ti_{1.0}Mn_{0.9}V_{1.1}$ alloy and $Ti_{1.0}Cr_{1.5}V_{1.7}$ alloy revealed different structural transition processes upon hydrogenation although the crystal structures of these two alloys are both BCC at room temperature. The second phases such as Ti-rich phase with $NiTi_2$ structure and $\alpha$-Ti with HCP structure absorbed hydrogen at relatively low hydrogen pressures and the phase abundance remained almost constant. This means that it is desirable to decrease the amount of the second phases as far as possible in order to increase the effective hydrogen storage capacities of the alloys. The crystal structures of corresponding isotope hydrides, the phase abundance and the lattice parameters did not depend on the kind of hydrogen isotope, but only on the hydrogen content.