• Journal of the Korean Society for Heat Treatment
• /
• v.14 no.4
• /
• pp.235-239
• /
• 2001

급속 표면가열과 기존의 전기로 열처리에서 얻어지는 경화의 가장 중요한 차이점은 전자가 불균질한 오스테나이트를 생성할 수도 있다는 것이다. 즉, 오스테나이트에 미용해 탄화물이 존재할 수도 있고 탄소와 합금원소의 농도 구배가 존재할 수도 있다. 합금강에서, 이러한 탄화물은 합금성분이 비교적 높기 때문에 철 탄화물에 비해서는 좀 더 천천히 기지에 용해된다. 또한 망간, 크롬, 니켈 및 몰리브덴과 같은 치환형 합금원소는 천천히 확산한다. 따라서, 균일한 오스테나이트를 생성하기 위해서는 더 많은 시간과 더 높은 온도가 요구된다. 그러나 표면 구역의 낮은 경화능에도 불구하고 냉각속도가 마르텐사이트의 체적분율이 큰 미세조직을 확보할 만큼 충분히 크기 때문에 경도는 높게 된다.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2012.05a
• /
• pp.326-326
• /
• 2012

현재 자동차 강판 시장은 이산화탄소 저감과 승객의 안전확보를 위하여 고장력강을 요구하고 있는 추세이며, 강도와 성형성을 동시에 확보하기 위하여 DP, TRIP강과 같은 변태강화형 강판을 선호한다. 그러나 강판의 상분율을 제어하기 위해서는 Si, Mn등과 같은 합금원소를 필요로 하게 되며 강판의 생산공정 중 이들 합금원소는 강판의 표면에 산화물로 농화되어 아연도금 특성을 크게 저하시키는 결과를 초래한다. 따라서 본 연구에서는 냉연 아연도금강판의 생산 공정을 모사하고 이들의 산화물 구조를 분석하여 도금특성에 어떠한 영향을 미치는지 고찰하고 Ni-precoating 공정을 이용하여 강판의 도금성 개선의 가능성을 제시하였다.

• Analytical Science and Technology
• /
• v.13 no.3
• /
• pp.269-276
• /
• 2000

Chromatographic retention mechanism of seven benzoic acids in RPLC were investigated. Inorganic salt is pertinent for the measurement of dead time in benzoic acid. Logarthims of capacity factor (log k') and Hildebrand solubility parameter (${\delta}$) showed proportional relationship which imply the hydrophobic effect of the retention mechanism in RPLC. Enthalpies of solute transfer showed inverse proportion to temperature and organic modifier ratio of the mobile phase. It was found that the S value showed positive slope in plot of log k' vs. volume fraction of water in mobile phase. Free energy change increases with increasing organic volume fraction. The hydrophobicity index, ${\varphi}_0$(organic volume fraction) is inversely proportional to column temperature.

• Journal of Energy Engineering
• /
• v.5 no.1
• /
• pp.80-86
• /
• 1996

Naphthalene hydrogenation reaction was performed as a model reaction for coal liquefaction. Product distributions of tetralin and decalin are sensitive to reaction temperature and hydrogen pressure. At 380$^{\circ}C$, hydrogenation reaction using sulfided pellet catalysts gives poor reproducibility and several experimental methods are tried to examine its cause. It was inferred that H$_2$S had, most possibly, a great effect on this phenomena and the effect of H$_2$S was systematically investigated at 250$^{\circ}C$. It is possible that the intermediate hydroaromatic compound (tetralin) is maximized by changing the partial pressure of H$_2$S. It was identified that the partial pressure of H$_2$S could be another important factor in addition to the reaction time and temperature in coal liquefaction using sulfided catalysts.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.37 no.11
• /
• pp.977-984
• /
• 2013

A hygroscopic rotor comprises many microchannels with high adsorption characteristics. In this study, the iterative adsorption/desorption processes that were affected by the humid air flow in a channel were numerically simulated. In consideration of the accuracy and computational costs, in the desiccant layer, only surface diffusion was considered in this simulation. The results were compared with the previous numerical results and found to show good agreement. By conjugating the heat and mass transfer between the desiccant and the flow layers, temporal and spatial changes in the vapor mass fraction, adsorbed liquid water mass fraction, and temperature in the channel were presented.

• Journal of Navigation and Port Research
• /
• v.39 no.4
• /
• pp.345-351
• /
• 2015

This study investigated the optimum depth for the application of bioremediation in contaminated coastal sediment using a lab scale column experiment. The biostimulants were placed in the top surface of the sediment facing seawater, 3cm, 6cm and 10cm of the depth from the surface, respectibely. During the experiment, the changes of organic pollutants and heavy metal fractions in the sediment were monitored in 1 month and 3month time intervals. The organic pollutants found during various analysis such as chemical oxygen demand, total solids and volatile solids, significantly reduced when the depth of the biostimulant was 3cm or less. In contrast, at a depth of over 6cm, the reduction of organic pollutants decreased, and the results were similar to the control. Heavy metals fractions in the sediment also changed with the depth of the biostimulants. The exchangeable fraction of the metals was quite reduced at the sediment surface in the column, but the organic bound and residual fractions considerably increased at a depth of 3cm. Based on this study, the optimum biostimulants depth for in-situ bioremediation of contaminant coastal sediment is 3cm from the sediment surface.

• Journal of the Korean Chemical Society
• /
• v.30 no.3
• /
• pp.301-306
• /
• 1986

The rate constants for the solvolysis reactions of p-methoxybenzylchloride in ethanol-water mixtures were determined at 2$^{\circ}$ and 10$^{\circ}C$ up to 1600bar. Rates of reaction were increased with increasing temperature and pressure, and decreased with increasing solvent composition of ethanol mole fraction. From the rate constants, the values of the activation parameters (${{\Delta}V_o}^{\neq},\;{\Delta}{\beta}^{\neq},\;{\Delta}H^{\neq},\;and\;{\Delta}S^{\neq}$) were evaluated. The values of ${{\Delta}V_o}^{\neq}$ and ${\Delta}{\beta}^{\neq}$ exhibit the extremum behavior at about 0.30 mole fraction of ethanol. This behavior is discussed in terms of solvent structure variation. From these results, it could be postulated that the reaction proceeds through $S_N1$ mechanism.

• Journal of the Korean Chemical Society
• /
• v.30 no.2
• /
• pp.188-194
• /
• 1986

The rate constants for the solvolysis reactions of p-chlorobenzyl chloride in ethanol-water mixtures were determinded at 30${\circ}\;and\;40{\circ}$C up to 1,600bar. Rates of reaction were increased with increasing temperature and pressure, and decreased with increasing solvent composition of ethanol mole fraction. The plots of ln k against pressure are fitted to a second-order function in P, and values of ${\Delta}V^{\neq}\;and\;${\Delta}{\beta}^{\neq}$ are obtained. The values of ${\Delta}V^{\neq}\;and\;${\Delta}{\beta}^{\neq}$ extremum behavior at about 0.20 mole fraction of ethanol. This behavior is discussed in terms of solvent structure variation. From the relation between the plots of ln k versus the solvent parameter, q ≡ (D-1)/(2D+1), or the logarithmic molar water concentration, In $C_w$, it could be estimated that the reaction proceeds through $S_N1(2)$ mechanism.

• Journal of the Korean Chemical Society
• /
• v.25 no.3
• /
• pp.152-159
• /
• 1981

The rates of solvolysis for p-nitrobenzyl chloride have been measured by the electric conductivity method in aqueous ethanol from 0.0 to 0. 5 mole fraction of ethanol under various pressures up to 1200bar at 50 and $60{\circ}C$. The activation parameters, ${\Delta}V_\0^{\neq},\ {\Delta}H^{\neq}$ and ${\Delta}S^{\neq}$ are evaluated from the rate constants. The results indicated that ${\Delta}V_\0^{\neq}$ exhibits an extremum behaviors near 0.3 mole fraction of ethanol and ${\Delta}H^{\neq}$ and ${\Delta}S^{\neq}$ near 0.1 mole fraction of ethanol. This behaviors are discussed in terms of solvent structure variation and the pressure dependences of ${\Delta}H^{\neq},\ {\Delta}H^{\neq}$ and ${\Delta}S^{\neq}$ are also discussed individually. The signs of the pressure dependence of ${\Delta}H^{\neq}$${\Delta}S^{\neq}$ are shown to be consistent with those required by the Maxwell relationships for classical thermodynamic systems.

• Nuclear Engineering and Technology
• /
• v.21 no.1
• /
• pp.12-17
• /
• 1989

The correction factor of neutron fraction absorbed by $^{55}$ Mn in the MnSO$_4$ bath was determined for the absolute measurement of neutron emission rate by using the solution circulation-type manganese sulfate bath system. For the determination of this correction factor, I/f, the atomic number desnsity and the effective neutron capture cross section data of Mn, S and impurity elements in the MnSO$_4$ solution were determined. For the atomic number density determination, the MnSO$_4$ solution concentration was determined by using the volumetric EDTA titration and gravimetric method. The impurity contents were analyzed by using the ICP method. For the calculation of effective neutron capture cross sections, a FORTRAN computer program EASCAL was developed in this study. in which Westcott's parameters and Axton's empirical relations are used.