• Journal of the Korea Concrete Institute
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• v.22 no.2
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• pp.179-186
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• 2010

The bond between steel and concrete in reinforced concrete members is essential to resist external load, but the bond mechanism in reinforced concrete beams deteriorated by steel corrosion has not been clearly known yet. Most existing researches have dealt with the bond behavior of corroded steel under monotonic loading, but scarce are researches dealing with bond behavior of corroded steel under repeated loading. This study includes the experimental investigation on the bond behavior with respect to the various degrees of steel corrosion under repeated loading. According to the test results, the bond strength of corroded steel under monotonic loading increases as the rate of steel corrosion increases unless the splitting crack occurs. The slip versus number of load cycles relation was found to be approximately linear in double logarithmic scale, not only in specimens without steel corrosion but also in specimens with steel corrosion. The test results also show that the steel corrosion does not negatively affect the bond strength of corroded steel after repeated loading unless the splitting crack occurs. But the fatigue life decreases sharply after splitting crack occurs. This research will be helpful for the realistic durability design and condition assessment of reinforced concrete structures.

• Journal of Welding and Joining
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• v.11 no.4
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• pp.91-102
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• 1993

The plasma sprayed $Cr_3C_2$-NiCr coatings are widely used as wear-resistant and corrosion-resistant materials. The mechanical and wear properties of the plasma sprayed $Cr_3C_2$-NiCr coating on steel plate were examined in this study. The pore in the coatings could be classified into two types, the one is the intrinsic pore originated from the spraying powder, the other is the extrinsic pore formed during spraying. During the tensile adhesion test, the fracture occured at the interface of top coating and bond coating. It is though that the compressive residual stress increases with the increase of the top coating thickness. From the wear test, it was found that the wear rate increased with the increase of the sliding velocity regardless of the temperature. It is thought that the fracture toughness reduces with the increase of the sliding velocity at $30^{\circ}C$ and that the adhesion amount increases with the increase of the sliding velocity at $400^{\circ}C$ It is concluded that the wear mechanism at $30^{\circ}C$ is the fracture and pull-out of the carbide particles due to the fatigue on sliding surface, while the wear mechanism at $400^{\circ}C$ is the adhesion of the smeared layer formed during wear process.

• Bulletin of the Korean Chemical Society
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• v.32 no.4
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• pp.1138-1142
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• 2011

Kinetic studies for the reactions of Y-aryl phenyl chlorothiophosphates with X-pyridines have been carried out in acetonitrile at $35.0^{\circ}C$. The Hammett and Bronsted plots for substituent X variations in the nucleophiles are biphasic concave upwards with a break point at X = 3-Ph, while the Hammett plots for substituent Y variations in the substrates are biphasic concave downwards (and partially upwards) with a break point at Y = H. The signs and magnitudes of the cross-interaction constant (${\rho}_{XY}$) are strongly dependent upon the nature of substituents, X and Y. The proposed mechanism is a stepwise process with a rate-limiting step change from bond breaking with the weaker electrophiles to bond formation with the stronger eletrophiles. The nonlinear free energy correlations of biphasic concave upward plots for substituent X variations in the nucleophiles are rationalized by a change in the attacking direction of the nucleophile from a backside with less basic pyridines to a frontside attack with more basic pyridines.

• Journal of the Korean Applied Science and Technology
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• v.7 no.2
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• pp.33-40
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• 1990

The Kinetics of the addition of benzalacetophenone derivatives was investigated by ultraviolet spectrophotometery in 5% dioxane $H_2O$ at $50^{\circ}C$. A rate equation was obtained in wide range of pH. The substituent effects on benzalacetophenone derivatives were studied, and addition were facilitated by electron attracting groups. The final product was benzalacetophenone-${\beta}$-thioglycolic acid synthesized by the addition of thioglycolic acid to benzalacetophenone. On the base of the rate equation, substituent effect, general base effect and final product, the plausible addition mechanism was proposed: Below pH 9.0, only neutral thioglycolic acid molecule was added to the carbon-carbon double bond, and in the range of pH $9.0{\sim}11.0$, neutral thioglycolic acid molecule and thioglycolic acid anion competitively attacted the double bond. By contrast, above pH 11.0, the reaction was dependent upon only the addition of thioglycolic acid anion.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.1240-1249
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• 2008

Jacket anchor was developed to increase the pullout resistance of general ground anchor in soft ground, and the mechanism of pullout resistance of jacket anchor was analyzed. Also, the ultimate bond stress of jacket anchor was estimated by ultimate resistance which is determined by field tests. Grout milk was injected into the jacket to make grout bulb of jacket anchor. The formation of grout bulb of jacket anchor increases the diameter of grout bulb, ground strength and confining pressure between anchor grout and soil. From the twelve field test results, it was observed that the pullout resistance of jacket anchor is 15.38~295.02%(average 83.53%) greater than that of general ground anchor, and plastic deformation of jacket anchor is 20.78~1,496.45%(average 288.78%) smaller than that of general ground anchor at the same load cycle. Especially, it was investigated that the increase of ultimate resistance over 200% and the reduction of plastic deformation over 600% was obtained in gravel layer. It means that the jacket anchor is superior to the general ground anchor in gravel layer. Finally, the ultimate bond stress was proposed to design jacket anchor.

• Journal of Environmental Science International
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• v.5 no.5
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• pp.579-583
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• 1996

This study is involved to develop new catalysts to decompose plastics, detergents and surfactants containing synthetic peptide bonds. As the first year research, the catalytic-hydrolysis of amide bond in copper complex was accomplished. The hydrolysis reaction in aqueous solution was monitored by UV/VIS spectroscopy. As the pH of the solution Is increased and the temperature is raised, the reaction rate increases. The reaction rate is observed as the first order kinetic behavior for the copper complex. The metal catalyzed hydrolysis mechanism is proposed cia metal-hydroxide in the pH region of 5.5 to 6.3. The results of characterization of the catalytic reaction mechanism can be applied to develop new catalysts for peptide bond degradation in further research.

• Journal of Microbiology and Biotechnology
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• v.23 no.12
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• pp.1699-1707
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• 2013

During the fermentative production of 1,3-propanediol under high substrate concentrations, accumulation of intracellular 3-hydroxypropionaldehyde will cause premature cessation of cell growth and glycerol consumption. Discovery of oxidoreductases that can convert 3-hydroxypropionaldehyde to 1,3-propanediol using NADPH as cofactor could serve as a solution to this problem. In this paper, the yqhD gene from Klebsiella pneumoniae DSM2026, which was found encoding an aldehyde reductase (KpAR), was cloned and characterized. KpAR showed broad substrate specificity under physiological direction, whereas no catalytic activity was detected in the oxidation direction, and both NADPH and NADH can be utilized as cofactors. The cofactor binding mechanism was then investigated employing homology modeling and molecular dynamics simulations. Hydrogen-bond analysis showed that the hydrogen-bond interactions between KpAR and NADPH are much stronger than that for NADH. Free-energy decomposition dedicated that residues Gly37 to Val41 contribute most to the cofactor preference through polar interactions. In conclusion, this work provides a novel aldehyde reductase that has potential applications in the development of novel genetically engineered strains in the 1,3-propanediol industry, and gives a better understanding of the mechanisms involved in cofactor binding.

• Journal of the Korean Chemical Society
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• v.23 no.6
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• pp.368-373
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• 1979

Kinetic studies have been carried out on solvolyses and halide exchanges $(Cl^-,\;Br^-,\;I^-)$ of N,N-dimethyl-, N,N-diethylcarbamoyl chlorides, and solvolyses of N,N-diphenylcarbamoyl chloride. Kinetic results together with simple MO analysis indicated that: (a) N,N-dialkylcarbamoyl chlorides reacted via the $S_N2$ mechanism, while N,N-diphenylcarbamoylchloride reacted via the $S_N1$ mechanism; (b) in chloride exchanges, the bond-breaking appeared to be important, whereas in bromide and iodide exchanges, the bond-formation was shown to be important.

• Bulletin of the Korean Chemical Society
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• v.32 no.10
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• pp.3743-3747
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• 2011

Kinetic studies on the reactions of Y-S-aryl phenyl phosphonochloridothioates with X-pyridines have been carried out in MeCN at $55.0^{\circ}C$. The Hammett and Bronsted plots for substituent X variations in the nucleophiles are biphasic concave upwards with a break point at X = H. The Hammett plots for substituent Y variations in the substrates are biphasic concave upwards with a break point at Y = H, and the sign of ${\rho}_Y$ is changed from unusual negative (${\rho}_Y$ < 0) with the weaker electrophiles to positive (${\rho}_Y$ > 0) with the stronger electrophiles. The stepwise mechanism is proposed on the basis of the ${\rho}_X$, ${\beta}_X$, and ${\rho}_{XY}$ values as follows: a ratelimiting leaving group departure from the intermediate involving a frontside attack and product-like TS for the stronger nucleophiles and weaker electrophiles; a rate-limiting leaving group departure from the intermediate involving a backside attack and product-like TS for the weaker nucleophiles and electrophiles; a rate-limiting bond formation involving a frontside attack for the stronger nucleophiles and electrophiles; a rate-limiting bond formation involving a backside attack for the weaker nucleophiles and stronger electrophiles. The substituent effects of X and Y on the pyridinolysis mechanisms of $R_1R_2P$(=S)Cl-type substrates are discussed.

• Journal of the Korean Chemical Society
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• v.34 no.1
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• pp.10-18
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• 1990

Solvolyses of p-substituted benzyl bromides have been studied in dimethylsulfoxide-water and N,N-dimethylformamide-water mixtures by kinetic method. To determine the ionizing power, Y and the nucleophilicity, $N_{BS}$, the solvolyses of 1-adamantyl halides, t-butyl halides, and methyl tosylate in the same solvent mixtures have been investigated. The solvatochromic parameters for each dimethylsulfoxide-water mixtures have been determined by substituting into the Taft's linear solvatochromic energy relationships with measured $ν_{max}$. The solvolyses of p-substituted benzyl bromides have been found to proceed by borderline mechanism in which bond formation is more advanced than bond cleavage in the transition state based on the m, l values and ${\beta},{\rho}_s$, values.