• Nuclear Engineering and Technology
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• v.29 no.3
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• pp.260-268
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• 1997

The effects of three mechanisms, calcium depletion, sulphate and carbonate penetration, on the concrete degradation have been studied. The shrinking core model (SCM) and the HYDROGEOC. HEM (HGC) model have been applied to evaluate how fast the mechanisms proceed. The SCM is an analytical approximation model and the HGC is a numerical mass transport model coupled with chemical reaction. The SCM leads to more conservative results than the HGC, and turns out to be very useful in the viewpoint of simplicity and conservatism. During 300 years, calcium has been depleted within 10 cm from the concrete outer surface, and sulphate has penetrated less than 13.5 cm into the concrete. Carbonate has not penetrated own 7 cm into the concrete in contact with the bentonite, and, furthermore, its penetration into the concrete with the groundwater is negligible. Conclusively, the concrete is expected to maintain its integrity for at least 300 years that are regarded as institutional control period of intermediate and low-level radioactive waste repository.

• Bulletin of the Korean Chemical Society
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• v.33 no.6
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• pp.1945-1948
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• 2012

Rhodamine B (RhB) and rhodamine 6G (Rh6G) were employed as catalysts for the synthesis of cyclic carbonate from carbon dioxide and epoxide. It turned out that the catalytic activity of Rh6G was nearly 29 times higher than that of RhB at 1 atm pressure, $90^{\circ}C$. Furthermore, the catalytic efficiency of RhB and Rh6G was greatly enhanced with triethylamine as co-catalyst. Under the optimized conditions, the best isolated yield (93%) of cyclic carbonate was achieved without organic solvent and metal component.

• Journal of Pharmaceutical Investigation
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• v.20 no.2
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• pp.73-78
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• 1990

A sensitive fluorometric method using 9-fluorenylmethyl pentafluorophenyl carbonate (FMPC) as the fluorescent labeling agent was developed to determine D-penicillamine (D-PA). The fluorophore had excitation and emission wavelengths of 260 nm and 313 nm, respectively. After derivatization, the fluorescent product was separated, and quantified by spectrofluorometry. The derivative was highly fluorescent and stable. Optimum condition for the reaction was investigated. A linear response was obtained over the range of $4.0{\times}10^{-7}-5.0{\times}10{-6}\;M$ with the correlation coefficient of 0.999 (n=6). The procedure described was successfully applied to the determination of the dosage forms of capsule with the recovery of $98.62{\pm}0.57%$ (150 mg), $98.36{\pm}0.57%$, (250 mg).

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.2
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• pp.89-95
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• 2021

Research on the production of lithium hydroxide (LiOH) has been actively conducted in response to the increasing demand for high nickel-based positive electrode materials for lithium-ion batteries. Herein we studied the conversion of lithium oxide (Li2O) through thermal decomposition of lithium carbonate for the production of lithium hydroxide from lithium carbonate (Li2CO3). The reaction mechanism of lithium carbonate with alumina, quartz and graphite crucible during heat treatment was confirmed. When graphite crucible was used, complete lithium oxide powder was obtained. Based on the TG analysis results, reagent-grade lithium carbonate was heat-treated at 700℃, 900℃ and 1100℃ for various time and atmosphere conditions. XRD analysis showed the produced lithium oxide showed high crystallinity at 1100℃ for 1 hour in a nitrogen atmosphere. In addition, several reagent-grade lithium oxides were reacted at 100℃ to convert to lithium hydroxide. XRD analysis confirmed that lithium hydroxide (LiOH) and lithium hydroxide monohydrate (LiOH·H2O) were produced.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.18 no.1
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• pp.40-46
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• 2013

The isotope ratios of $^{13}C/^{12}C$ and $^{18}O/^{16}O$ for a sample in a mass spectrometer are measured relative to those of a pure $CO_2$ reference gas (i.e., laboratory working standard). Thus, the calibration of a laboratory working standard gas to the international isotope scales (Pee Dee Belemnite (PDB) for ${\delta}^{13}C$ and Vienna Standard Mean Ocean Water (V-SMOW) for ${\delta}^{18}O$) is essential for comparisons between data sets obtained by other groups on other mass spectrometers. However, one often finds difficulties in getting well-calibrated standard gases, because of their production time and high price. Additional difficulty is that fractionation processes can occur inside the gas cylinder most likely due to pressure drop in long-term use. Therefore, studies on laboratory production of pure $CO_2$ isotope standard gas from stable solid calcium carbonate standard materials, have been performed. For this study, we propose a method to extract pure $CO_2$ gas without isotope fractionation from a solid calcium carbonate material. The method is similar to that suggested by Coplen et al., (1983), but is better optimized particularly to make a large amount of pure $CO_2$ gas from calcium carbonate material. The $CaCO_3$ releases $CO_2$ in reaction with 100% pure phosphoric acid at $25^{\circ}C$ in a custom designed, evacuated reaction vessel. Here we introduce optimal procedure, reaction conditions, and samples/reactants size for calcium carbonate-phosphoric acid reaction and also provide the details for extracting, purifying and collecting $CO_2$ gas out of the reaction vessel. The measurements for ${\delta}^{18}O$ and ${\delta}^{13}C$ of $CO_2$ were performed at Seoul National University using a stable isotope ratio mass spectrometer (VG Isotech, SIRA Series II) operated in dual-inlet mode. The entire analysis precisions for ${\delta}^{18}O$ and ${\delta}^{13}C$ were evaluated based on the standard deviations of multiple measurements on 15 separate samples of purified $CO_2$. The pure $CO_2$ samples were taken from 100-mg aliquots of a solid calcium carbonate (Solenhofen-ori $CaCO_3$) during 8-day experimental period. The multiple measurements yielded the $1{\sigma}$ precisions of ${\pm}0.01$‰ for ${\delta}^{13}C$ and ${\pm}0.05$‰ for ${\delta}^{18}O$, comparable to the internal instrumental precisions of SIRA. Therefore, we conclude the method proposed in this study can serve as a way to produce an accurate secondary and/or laboratory $CO_2$ standard gas. We hope this study helps resolve difficulties in placing a laboratory working standard onto the international isotope scales and does make accurate comparisons with other data sets from other groups.

• Korean Chemical Engineering Research
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• v.48 no.5
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• pp.621-626
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• 2010

In this study, imidazole-based ionic liquid on polystyrene was prepared and its catalytic performance in the cycloaddition of $CO_2$ with allyl glycidyl ether(AGE) to produce allyl glycidyl carbonate was investigated. The ionic liquid was generated on the polystyrene-based polymer through the immobilization of imidazole. The prepared catalyst was characterized using a number of instrumental analysis including EA, FT-IR, TGA and SEM. The immobilized ionic liquid showed very good catalytic activity for the cycloaddition of $CO_2$ with AGE, having 80% of AGE conversion with over 96% of the carbonate selectivity at $120^{\circ}C$ under 1.48 MPa $CO_2$ pressure. The immobilized ionic liquid can be used for the reaction up to four consecutive runs without significant loss of its catalytic activity.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.1332-1343
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• 2008

The purpose of this study was to investigate the feasibility of using sedimentation calcium carbonate production based on microorganism activities in the strength manifestation of various soil conditions including ground. For analysis and comparison of microbial cementation soil's strength, unconfined compression test was executed by each content of soil(S), water(W), microorganism(B), microorganism and deposit (BF), microorganism, admixture and deposit(BCF) at specimen. The result, the strength of SB(soil+microorganism) and SBF(soil+microorganism+deposit) increased about 8%, 15% than SW(soil+water). Also, initial strength increased. But the strength of SBC(soil+microorganism+admixture) and SBCF(soil+microorganism+deposit+admixture) increased about 71%, 115% than SW(soil+water). The results of the SEM analysis, leading to the formation of an adhesive substance layers at the surface and resulting in firm particle configuration. The XRD examination of the sediment resulting from the reaction between the microorganism and the deposit control agent confirmed the presence of a type of calcium carbonate ($CaCo_3$) vaterite, which affects soil strength formation, as well as sodium silicate, silicides and so forth. This indicates that microorganism plays an important role in the production of carbonate ($CaCo_3$), sodium silicate and silicides. It affects to revelation of ground strength.

• Journal of the Korean Geotechnical Society
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• v.36 no.1
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• pp.17-28
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• 2020

This study presents the experimental results of ground improvement efficiency induced by enzyme-induced carbonate precipitation (EICP) in soils. First, the optimal mixture ratio of EICP solution was determined by comparing the amount of induced carbonate depending on the different ratio among urea, CaCl₂, and urease. Next, we evaluated the shear stiffness and strength of EICP-treated sandy soil by performing shear wave velocity measurement and triaxial shear test. Furthermore, induced carbonate in treated soil was visually investigated by X-ray CT and SEM analysis. The results showed that the maximum shear stiffness evolved 19~30 times after 6 hours of reaction time compared with non-treated sands. Also, the cohesion and the friction angle tended to increase and decrease, respectively, as the amount of induced carbonate increased.

• Bulletin of the Korean Chemical Society
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• v.34 no.4
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• pp.1115-1119
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• 2013

A kinetic study is reported for nucleophilic substitution reactions of benzyl 2-pyridyl thionocarbonate (5b) and t-butyl 2-pyridyl thionocarbonate (6b) with a series of alicyclic secondary amines in $H_2O$ at $25.0^{\circ}C$. General-base catalysis, which has often been reported to occur for aminolysis of esters possessing a C=S electrophilic center, is absent for the reactions of 5b and 6b. The Br${\o}$nsted-type plots for the reactions of 5b and 6b are linear with ${\beta}_{nuc}$ = 0.29 and 0.43, respectively, indicating that the reactions of 5b proceed through a stepwise mechanism with formation of a zwitterionic tetrahedral intermediate ($T^{\pm}$) being the rate-determining step while those of 6b proceed through a concerted mechanism. The reactivity of 5b and 6b is similar to that of their oxygen analogues (i.e., benzyl 2-pyridyl carbonate 5a and t-butyl 2-pyridyl carbonate 6a, respectively), indicating that the effect of modification of the electrophilic center from C=O to C=S (i.e., from 5a to 5b and from 6a to 6b) on reactivity is insignificant. In contrast, 6b is much less reactive than 5b, indicating that the replacement of the $PhCH_2$ in 5b by the t-Bu in 6b results in a significant decrease in reactivity as well as a change in the reaction mechanism (i.e., from a stepwise mechanism to a concerted pathway). It has been concluded that the contrasting reactivity and reaction mechanism for the reactions of 5b and 6b are not due to the electronic effects of $PhCH_2$ and t-Bu but are caused by the large steric hindrance exerted by the bulky t-Bu in 6b.

• Bulletin of the Korean Chemical Society
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• v.34 no.8
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• pp.2325-2329
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• 2013

Second-order rate constants $k_N$ have been measured for reactions of benzyl 2-pyridyl thionocarbonate (4b) and t-butyl 2-pyridyl thionocarbonate (5b) with a series of cyclic secondary amines in MeCN at $25.0{\pm}0.1^{\circ}C$. The $k_N$ values for the reactions of 4b and 5b have been compared with those reported previously for the corresponding reactions of benzyl 2-pyridyl carbonate (4a) and t-butyl 2-pyridyl carbonate (5a) to investigate the effect of changing the electrophilic center from C=O to C=S on reactivity and reaction mechanism. The thiono compound 4b is more reactive than its oxygen analogue 4a. The Br${\o}$nsted-type plots for the reactions of 4a and 4b are linear with ${\beta}_{nuc}=0.57$ and 0.37, respectively. The reactions of 4a were previously reported to proceed through a concerted mechanism, while those of 4b in this study have been concluded to proceed through a stepwise mechanism with formation of an intermediate being the rate-determining step on the basis of the ${\beta}_{nuc}$ value of 0.37. Enhanced polarizability upon changing the C=O in 4a by C=S has been suggested to be responsible for the reactivity order and the contrasting reaction mechanisms. In contrast, the reactivity of 5a and 5b is similar, but they are much less reactive than 4a and 4b. Furthermore, the reactions of 5a and 5b have been concluded to proceed through the same mechanism (i.e., a concerted mechanism) on the basis of linear Bronsted-type plots with ${\beta}_{nuc}=0.45$ or 0.47. It has been concluded that the strong steric hindrance exerted by the t-Bu in 5a and 5b causes a decrease in their reactivity and forces the reactions to proceed through a concerted mechanism.