• 한국세라믹학회지
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• 제43권7호
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• pp.389-392
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• 2006

Electric field-induced phase transition from the tetragonal to rhombohedral phase was investigated for the <111> direction in tetragonal PZN-PT single crystals, which have spontaneous polarization along the <001> direction. From the strain and dielectric data, it was confirmed that the samples followed a tetragonal-orthorhombic-rhombohedral phase transition sequence with application of an electric field. This transition is different from the rhombohedral-tetragonal phase transition of <001> rhombohedral composition single crystals, in which a phase transition occurred without showing the intermediate orthorhombic phase.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 추계학술대회논문집
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• pp.269-273
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• 2003

There is a growing interest to replace the commercial steels with non-heat treated steels, which does not involve the spheroidization and quenching-tempering treatment. However, Non-heat treated steels should satisfy high strength and good formability without performing heat treatment. Therefore, it is important to investigate optimum materials showing a good combination of strength and formability after the drawing process. In this study, Dual-Phase Steels were studied as candidate materials for non-heat treated steels, which have different martensite morphologies and volume fractions obtained through heat-treatment of intercritical quenching (IcQ), intermediate quenching (ImQ) and step quenching (SQ). The mechanical properties of DP steels were measured by tension and compression tests. Also, the cold formability of three DP steels which have similar tensile strength value was investigated by estimating the deformation resistance and the forming limit. The deformation resistance which is important factor in determining die life was estimated by calculating the deformation energy. And the forming limit was estimated by measuring the critical strain revealing crack initiation at the notch tip of the specimens.

• 소성∙가공
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• 제13권1호
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• pp.84-89
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• 2004

There is a growing interest to replace the commercial steels with non-heat treated steels, which does not involve the spheroidization and quenching-tempering treatment. However, Non-heat treated steels should satisfy high strength and good formability without performing heat treatment. Therefore, it is important to investigate optimum materials showing a good combination of strength and formability after the drawing process. In this study, Dual-Phase Steels were studied as candidate materials for non-heat treated steels, which have different martensite morphologies and volume fractions obtained through heat-treatment of intercritical quenching (IcQ), intermediate quenching (ImQ) and step quenching (SQ). The mechanical properties of DP steels were measured by tension and compression tests. Also, the cold formability of three DP steels which have similar tensile strength value was investigated by estimating the deformation resistance and the forming limit. The deformation resistance which is important factor in determining die life was estimated by calculating the deformation energy. And the forming limit was estimated by measuring the critical strain revealing crack initiation at the notch tip of the specimens.

• 한국재료학회지
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• 제24권4호
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• pp.201-206
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• 2014

TiC-21 mol% Mo solid solution (${\delta}$-phase) and TiC-99 mol% Mo solid solution (${\beta}$-phase), and TiC-(80~90) mol% Mo hypo-eutectic composite were deformed by compression in a temperature range from room to 2300 K and in a strain rate range from $4.9{\times}10^{-5}$ to $6.9{\times}10^{-3}/s$. The deformation behaviors of the composites were analyzed from the strengths of the ${\delta}$- and ${\beta}$-phases. It was found that the high strength of the eutectic composite is due primarily to solution hardening of TiC by Mo, and that the ${\delta}$-phase undergoes an appreciable plastic deformation at and above 1420 K even at 0.2% plastic strain of the composite. The yield strength of the three kinds of phase up to 1420 K is quantitatively explained by the rule of mixture, where internal stresses introduced by plastic deformation are taken into account. Above 1420 K, however, the calculated yield strength was considerably larger than the measured strength. The yield stress of ${\beta}$-phase was much larger than that of pure TiC. A good linear relationship was held between the yield stress and the plastic strain rate in a double-logarithmic plot. The deformation behavior in ${\delta}$-phase was different among the three temperature ranges tested, i.e., low, intermediate and high. At an intermediate temperature, no yield drop occurred, and from the beginning the work hardening level was high. At the tested temperature, a good linear relationship was held in the double logarithmic plot of the yield stress against the plastic strain rate. The strain rate dependence of the yield stress was very weak up to 1273 K in the hypo-eutectic composite, but it became stronger as the temperature rose.

• 한국세라믹학회지
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• 제25권4호
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• pp.408-414
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• 1988

This thesis is 2nd thesis from "Mechanism of Intercalation Compounds in Graphite with Hydrogen sulfate(J. Korea Cer. Soc. Vol. 22. No.6, 1985). We have oxidized natural Graphite flakes(0.1~0.2mm., Kropfm hl passau in Deutchland. S40) with a solution of CrO3 in H2SO4. Whilst persulfate ions were intercalated, too, below 7$^{\circ}C$, no evidence for intercalation of a peroxo compound was found at 22$^{\circ}C$. The reaction was interrupted after various times by filtering and washing with concentrated H2SO4. X-ray diffraction showed that the 2nd stage compound had already been formed after 2 minutes. We could only follow further oxidation to the blue stage compound which was completed after 35 minutes. We have found six distinct intermediate stage between 2nd stage and 1 stage. Experiments are described on the formation of intermediate stage color and X-ray diffraction analysis.ysis.

• 한국항행학회논문지
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• 제3권2호
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• pp.120-131
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• 1999

마그네트론을 이용하여 송신 펄스를 발생하는 레이다에서 위상을 측정하기 위해서는 송신주파수의 변화에 대해서도 안정된 중간주파수를 발생할 수 있도록 STALO(Stable Local Oscillator)의 주파수를 조정하여야 한다. 레이다 수신기의 AFC(Automatic Frequency control) 회로는 마그네트론에서 발생하는 송신주파수와 STALO의 국부발진주파수를 비교하여 일정한 중간주파수가 발생하도록 STALO 주파수를 제어한다. 본 논문에서는 안정된 중간주파수를 발생하기 위한 AFC 회로를 설계, 제작하였으며, 주파수 변화를 검출하여 비교하는 아날로그 부분과 STALO에 주파수 제어신호를 공급하는 디지털 부분을 개발하였다.

• 상하수도학회지
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• 제26권3호
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• pp.453-461
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• 2012

The degradation characteristics of TCE by Ferrate(VI) oxidation have been studied. Ferrate(VI) were prepared by electrochemical method. The degradation efficiency of TCE in aqueous solution was investigated at various pH values, Ferrate(VI) doses and aqueous solution temperature values. GC-ECD was used to analyze TCE. TCE was degraded rapidly by ferrate(VI) in aqueous solution, Also, the experimental results showed that TCE removal efficiency increased with the increase of Ferrate(VI) doses. The effect of pH was investigated and the maximum degradation efficiency was obtained at pH 7. And intermediate products were identified by GC-MS techniques. Ethyl Chloride, Dichloroethylene, Chloroform, 1,1-dichloropropene, Trichloroacetic acid and Trichloroethane were identified as a reaction intermediate, and $Cl^-$ was identified as an end product.

• JSTS:Journal of Semiconductor Technology and Science
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• 제13권6호
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• pp.539-545
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• 2013

In this paper, a behavioral current-voltage model with intermediate states is proposed for analog applications of unipolar resistive memories, where intermediate resistance values between SET and RESET state are used to store analog data. In this model, SET and RESET behaviors are unified into one equation by the blending function and the percentage volume fraction of each region is modeled by the Johnson-Mehl-Avrami (JMA) equation that can describe the time-dependent phase transformation of unipolar memory. The proposed model is verified by the measured results of $TiO_2$ unipolar memory and tested by the SPECTRE circuit simulation with CMOS read and write circuits for unipolar resistive memories. With the proposed model, we also show that the behavioral model that combines the blending equation and JMA kinetics can universally describe not only unipolar memories but also bipolar ones. This universal behavioral model can be useful in practical applications, where various kinds of both unipolar and bipolar memories are being intensively studied, regardless of polarity of resistive memories.

• Bulletin of the Korean Chemical Society
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• 제16권3호
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• pp.252-256
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• 1995

Semiempirical MO calculations using the PM3 method are performed on the reactions of acetate esters with substituted phenolate anions. The mechanistic change from rate-limiting formation to breakdown of the anionic intermediate is shown to occur in the gas-phase, especially for meta-nitrophenyl acetate. However the mechanistic change-over takes place at a lower basicity ($pK_0$) of the anion nucleophile than found for the corresponding formate. This lowering of $pK_0$ has been ascribed to the electron donating effect of the methyl group in the acetate. For the reactions involving rate-limiting breakdown of the intermediate, the large Bronsted coefficients, ${\beta}_X({\beta}_{nuc})$, are expected in general, but the magnitude increases to a larger value and the pK0 is lowered accordingly, when an electron-donating nonleaving group, like $CH_3$, is present. This type of nonleaving group effect provides a necessary condition for the carbonyl addition-elimination mechanism with rate-limiting breakdown of the intermediate.

• 한국주조공학회지
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• 제26권1호
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• pp.27-33
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• 2006

Phase evolutions involving nucleation stages together with diffusional growth have been examined in order to provide a guideline for determining rate limiting stages during phase evolutions. In multiphase materials systems in coatings, composites or multilayered structures, diffusion treatments often result in the development of metastable/intermediate phases at the reaction interfaces. The development of metastable phases during solid state interdiffusion demonstrates that the nucleation reaction can be one controlling factor. Also, the concentration gradient and the relative magnitudes of the component diffusivities provide a basis for a phase selection and the application of a kinetic bias strategy in the phase selection. For multicomponent alloy systems, the identification of the operative diffusion pathway is central to control phase formation. Experimental access to the nucleation and growth stage is discussed in thin film multi layers and bulk samples.