• Journal of Radiation Protection and Research
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• v.20 no.1
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• pp.1-7
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• 1995

Strontium selective chromatographic material $(Sr-Spec^{TM})$ was investigated for separation of radiostrontium from environmental soil and water sample. This chromatographic material has great capacity of binding of strontium ion in nitric acid media, and has selectivity to permit the separation of stontium from bulk amount of calcium. But the extraction of strontium was reduced by the other interfering ions such as K and Ba. So, in order to apply this material to the soil sample, prior removal treatment of K and Ba was needed. But the Sr-Spec material could provides simple and effective methods for the separation and removal of radiostrontium from liquid sample.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.6
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• pp.744-752
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• 2007

Recently a fuel oil of the diesel engine in the ship is being changed with low quality as the oil price is higher more and more. Therefore the wear and corrosion in all parts of the engine like cylinder liner ring groove of piston crown, spindle and seat ring of exhaust valve are increased with using of heavy oil of low quality In particular the degree of wear and corrosion in between valve spindle and seat ring are more serious compared to the other parts of the engine due to operating in severe environment such as the high temperature of exhaust gas and repeating impact. Thus the repair weld to the valve spindle and seat ring is a unique method to prolong the life of the exhaust valve in an economical point of view In this study. corrosion property of both weld metal zone and base metal was investigated with some electrochemical methods such as measurement of corrosion potential, cathodic and anodic polarization curves, cyclic voltammogram and polarization resistance etc. in 5% $H_2SO_4$ solution. in the case of being welded with some welding methods and welding materials to the exhaust valve specimen as the base metal. In all cases. the values of hardness of the weld metal zone were more high than that of the base metal. And their corrosion resistance were also superior to the base metal. The weld metal of A2F(AC SMAW: 2 pass welding with foreign electrode) showed a relatively good results to the corrosion resistance as well as the hardness compared to the ether welding methods and welding materials. Moreover it indicated that hardness of the weld metal by the domestic electrode was considerably high compared to that of the foreign electrode.

• Journal of the Korean Chemical Society
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• v.36 no.5
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• pp.621-626
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• 1992

The effects of $Ca^{2+}$ ion on the charge transfer(CT) interaction of $4-(C_9H_{19})C_6H_4O(CH_2CH_2O)_{40} [NP-(EO)_{40}]$ with iodine in aqueous solution were investigated by UV-visible spectrophotometer. Maximum absorption wavelengths to the CT interaction were in the vicinity of 390 nm, and by the addition of $Ca^{2+}$ ion shifted toward 370 nm. Above CMC, the intensity of the CT interaction by the addition of $Ca^{2+}$ ion were increased and then decreased. The increase in the intensity of CT band were attributed to the increase of the donor-acceptor overlap with iodine caused by the compactness of micelle in the presence of $Ca^{2+}$ ion. These phenomena suggest that the linear oxyethylene(EO) chains, relatively free to assume various configuration in aqueous solution, could form a pseudo-crown ether structures capable of forming complexes with $Ca^{2+}$ ion.

• Bulletin of the Korean Chemical Society
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• v.31 no.9
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• pp.2483-2487
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• 2010

Pseudo-first-order rate constants ($k_{obsd}$) were measured spectrophotometrically for nucleophilic substitution reactions of 4-nitrophenyl picolinate (6) with alkali metal ethoxides (EtOM, $M^+\;=\;K^+$, $Na^+$ and $Li^+$) in anhydrous ethanol at $25.0{\pm}0.1^{\circ}C$. The plot of $k_{obsd}$ vs. [EtOM] exhibits upward curvature regardless of the nature of $M^+$ ions. However, the plot for the reaction of 6 with EtOK is linear with significantly decreased $k_{obsd}$ values when 18-crown-6-ether (18C6, a complexing agent for $K^+$ ion) is added in the reaction medium. Dissection of $k_{obsd}$ into $k_{EtO^-}$ and $k_{EtOM}$ (i.e., the second-order rate constant for the reaction with dissociated $EtO^-$ and ion-paired EtOM, respectively) has revealed that ion-paired EtOM is 3~17 times more reactive than dissociated $EtO^-$. The reaction has been proposed to proceed through a 5-membered cyclic transition state, in which $M^+$ ion increases the electrophilicity of the reaction site. Interestingly, $Na^+$ ion exhibits the largest catalytic effect. The presence of a nitrogen atom in the pyridine moiety of 6 has been suggested to be responsible for the high $Na^+$ ion selectivity.

• Bulletin of the Korean Chemical Society
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• v.35 no.8
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• pp.2438-2442
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• 2014

A kinetic study is reported for $S_NAr$ reaction of 1-fluoro-2,4-dinitrobenzene (5a) and 1-chloro-2,4-dinitrobenzene (5b) with alkali-metal ethoxides (EtOM, M = Li, Na, K and 18-crown-6-ether complexed K) in anhydrous ethanol. The second-order rate constant increases in the order $k_{EtOLi}$ < $k_{EtO^-}$ < $k_{EtONa}$ < $k_{EtOK}$ < $k_{EtOK/18C6}$ for the reaction of 5a and $k_{EtOLi}$ < $k_{EtONa}$ < $k_{EtO^-$ < $k_{EtOK}$ < $k_{EtOK/18C6}$ for that of 5b. This indicates that $M^+$ ion behaves as a catalyst or an inhibitor depending on the size of $M^+$ ion and the nature of the leaving group ($F^-$ vs. $Cl^-$). Substrate 5a is more reactive than 5b, although the $F^-$ in 5a is ca. $10pK_a$ units more basic than the $Cl^-$ in 5b, indicating that the reaction proceeds through a Meisenheimer complex in which expulsion of the leaving group occurs after the rate-determining step (RDS). $M^+$ ion would catalyze the reaction by increasing either the nucleofugality of the leaving group through a four-membered cyclic transition state or the electrophilicity of the reaction center through a ${\pi}$-complex. However, the enhanced nucleofugality would be ineffective for the current reaction, since expulsion of the leaving group occurs after the RDS. Thus, it has been concluded that $M^+$ ion catalyzes the reaction by increasing the electrophilicity of the reaction center through a ${\pi}$-complex between $M^+$ ion and the ${\pi}$-electrons in the benzene ring.

• Journal of Radiation Protection and Research
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• v.24 no.1
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• pp.9-15
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• 1999

In order to separate $Sr^{2+}$ selectively from environmental sample solutions containing $Ca^{2+}$, supported liquid membranes(SLM) were prepared and their characteristics of separation were investigated. The contents of carriers, DC18C6 and DNNS, in SLM affected the permeabilities of metal ions and selectivities of $Sr^{2+}$. The selectivity of $Sr^{2+}$ reached to 93.3% in a SLM with 0.1 M DC18C6 and 25 mM DNNS. When the ratio of $Sr^{2+}$ to $Ca^{2+}$ concentration in the feed solution was in the range of 1/25 to 1/50, the selectivity of $Sr^{2+}$ was greater than 90 %. Therefore, it is considered that the SLM prepared in this study is capable of treating environmental sea-water samples for strontium measurement.

• Journal of the Korean Chemical Society
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• v.37 no.1
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• pp.36-42
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• 1993

In the presence of $Ca^{2+}$ ion, the charge transfer (CT) interaction of nonionic surfactants, $nonylphenol-(ethylene oxide)_n\;[NP-(EO)_n; n = 11, 40, 100]$ with iodine in aqueous solution were investigated by UV-visible spectrophotometer. The characteristics of spectra depended on the concentration of $Ca^{2+}$ ion and the number of EO unit. Above CMC, the intensity of the CT band by the addition of $Ca^{2+}$ ion for the $NP-(EO)_{11}$ and $NP-(EO)_{40}$ increased and then decreased, while for the $NP-(EO)_{100}$ continuously increased. The increase in the intensity of CT band were attributed to the compactness of micelle in the presence of $Ca^{2+}$ ion. These phenomena may be explained by the fact that the linear ethylene oxide (EO) chain, to be free configuration in aqueous solution, could form a pseudo-crown ether structures capable of forming complexes with $Ca^{2+}$ ion.

• Journal of the Korean Chemical Society
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• v.37 no.10
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• pp.855-860
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• 1993

In the presence of SDS(sodium dodecyl sulfate), effect of $Ca^{2+}$on the interaction of NP-40EO[nonylphenol-(ethylene oxide)40] with iodine in aqueous solution were investigated by UV-visible spectrophotometer. In the presence of SDS, the intensity of interaction peaks were decreased and markedly increased by the addition of $Ca^{2+}$. Decrease of interaction peaks is caused by decrease of EO number to be interact with iodine per unit surface area of mixed micelle to the insertion of SDS and increase is attributed to the compactness of micelle in the presence of $Ca^{2+}$. These phenomena may be explained by the fact that the linear EO (ethylene oxide) chains, to be free in aqueous solution, could form a pseudo-crown ether structures of forming with $Ca^{2+}$ion.

• Bulletin of the Korean Chemical Society
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• v.31 no.12
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• pp.3543-3548
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• 2010

A kinetic study on nucleophilic displacement reactions of 2-pyridyl X-substituted benzoates 1a-e with potassium ethoxide (EtOK) in anhydrous ethanol is reported. Plots of pseudo-first-order rate constants ($k_{obsd}$) vs. $[EtOK]_o$ exhibit upward curvature. The $k_{obsd}$ value at a fixed $[EtOK]_o$ decreases steeply upon addition of 18-crown-6-ether (18C6) to the reaction mixture up to [18C6]/$[EtOK]_o$ = 1 and then remains nearly constant thereafter. In contrast, $k_{obsd}$ increases sharply upon addition of LiSCN or KSCN. Dissection of $k_{obsd}$ into $k_{EtO^-}$ and $k_{EtOM}$ has revealed that ion-paired EtOK is more reactive than dissociated $EtO^-$, indicating that $K^+$ ion acts as a Lewis acid catalyst. Hammett plots for the reactions of 1a-e with dissociated $EtO^-$ and ion-paired EtOK result in excellent linear correlation with $\rho$ values of 3.01 and 2.67, respectively. The $k_{EtOK}/k_{EtO^-}$ ratio increases as the substituent X in the benzoyl moiety becomes a stronger electron-donating group. $K^+$ ion has been concluded to catalyze the current reaction by stabilizing the transition state through formation of a 6-membered cyclic complex.

• Bulletin of the Korean Chemical Society
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• v.34 no.5
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• pp.1525-1529
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• 2013

Pseudo-first-order rate constants ($k_{obsd}$) have been measured spectrophotometrically for the nucleophilic substitution reactions of 2-pyridyl thionobenzoate (5b) with alkali-metal ethoxides (EtOM, $M^+=Li^+$, $Na^+$, $K^+$, and 18-crown-6-ether complexed $K^+$) in anhydrous ethanol at $25.0{\pm}0.1^{\circ}C$. The plots of $k_{obsd}$ vs. $[EtOM]_o$ curve upward regardless of the nature of the $M^+$ ions, while those of $k_{obsd}/[EtO^-]_{eq}$ vs. $[EtO^-]_{eq}$ are linear with a positive intercept. Dissection of $k_{obsd}$ into $k_{EtO^-}$ and $k_{EtOM}$ (i.e., the second-order rate constants for the reactions with the dissociated $EtO^-$ and ion-paired EtOM, respectively) has revealed that the ion-paired EtOM is more reactive than the dissociated $EtO^-$, and $M^+$ ions catalyze the reactions in the order $K^+$ < $Na^+$ < $Li^+$ < 18C6-complexed $K^+$. The plot of log $k_{EtOM}$ vs. $1/r_{Stokes}$ results in an excellent linear correlation, indicating that the reactions are catalyzed by the solvated $M^+$ ions but not by the bare $M^+$ ions. The reactions of 5b with EtOM have been concluded to proceed through a six-membered cyclic TS, in which the solvated $M^+$ ions increase the electrophilicity of the reaction center and the nucleofugality of the leaving group.