• Journal of the Korean Chemical Society
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• v.25 no.6
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• pp.361-366
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• 1981

For the urethane formation reaction of isocyanate with alcohol, orientation of approach of alcohol toward isocyanate was investigated theoretically by means of MO method. As a result of EHT and CNDO/2 calculations, it was found that the reaction proceeding via 4-centered mechanism, in which ROH is coplanar with isocyanate plane was energetically favored. It was also shown that the oxygen of ROH attacks the isocyanate carbon prior to the formation of 4-center complex. The reaction was found to be a charge controlled one.

• Preventive Nutrition and Food Science
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• v.13 no.2
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• pp.134-137
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• 2008

This study was conducted to investigate the effect of pH on the formation of acrylamide and acrylate from glucose and fructose reacting with amino acid enantiomers by the Maillard reaction. The acrylamide content was increased with increasing pH, except for Fru/D-Asn system. Both acrylamide and acrylate contents were higher in the glucose-based system compared to the fructose-based system at pH 10.0. However, according to amino acid enantiomers, only the acrylamide content showed a difference in the fructose-based system. In addition, the acrylate content was increased with increasing pH except in the Glc/L-Asn system. Acrylate formation was observed specifically at pH 4.0 for both the Glc/D-Asn and Fru/D-Asn systems.

• Journal of the Korean Ceramic Society
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• v.37 no.4
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• pp.332-337
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• 2000

Forming mechanism of fibrous TiC during self-propagating high temperature synthetic reaction was analyzed and suggested. It was revealed that critical temperature for the stable fiber formation was not the melting point of TiC, but the eutectic reaction temperature of TiC and C. Minimum amount of TiC diluent addition required to form fibers was calculated to be 25.6%, which was consistent with the experimental result. Synthesized fibers were found hollow tube-like. The morphology was explained by the diffusion rates of C and Ti in TiC, and by the molar volume chnage of C during the reaction. Expanding shell model was suggested for the hollow fiber formation mechanism.

• Progress in Superconductivity and Cryogenics
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• v.24 no.4
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• pp.25-28
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• 2022

We investigated the formation of superconducting intergrowth phases through the interface reaction both between TlSr₂Cu₁O₅ (Tl-121) and (CrO₄)Sr₂CuO₂, and between Tl -121 and ((CO₃)_0.5(CrO₄)_0.5 Sr₂CuO₂ phases. We found oxychromate intergrowth phases can be formed through the interface reactions and a new superconducting oxychromate compound TlSr₄Cu₂O_z(CO₃)_0.5(CrO₄)_0.5 with T_c above 73 K was discovered based on the results of the interface reactions.

• Journal of Korea Foundry Society
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• v.17 no.4
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• pp.371-378
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• 1997

The study for direct synthesis of TaC carbide which was a reaction product of tantalum and carbon in the cast iron was performed. Cast iron which has hypo-eutectic composition was cast bonded in the metal mold with tantalum thin sheet of thickness of $100{\mu}m$. The contents of carbon and silicon of cast iron matrix was controlled to have constant carbon equivalent of 3.6. The chracteristics of microstructure and the formation mechanism of TaC carbide in the interfacial reaction layer in the cast iron/tantalum thin sheet heat treated isothermally at $950^{\circ}C$ for various time were examined. TaC carbide reaction layer was grown to the dendritic morphology in the cast iron/tantalum thin sheet interface by the isothermal heat treatment. The composition of TaC carbide was 48.5 at.% $Ti{\sim}48.6$ at.% C-2.8 at.% Fe. The hardness of reaction layer was MHV $1100{\sim}1200$. The thickness of reaction layer linearly increased with increasing the total content of carbon in the cast iron matrix and isothermal heat treating time. The growth constant for TaC reaction layer was proportional to the log[C] of the matrix. The formation mechanism of TaC reaction layer at the interface of cast iron/tantalum thin sheet was proved to be the interfacial reaction.

• Bulletin of the Korean Chemical Society
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• v.21 no.1
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• pp.101-104
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• 2000

Li-graphite intercalation compounds (GICs), synthesized at elevated temperature and pressure, were allowed to decompose spontaneously in the atmosphere. The decomposition processes were analyzed by of X-ray diffraction, DSC analysis, FT-IR measurements, UV/VIS spectrophotometry. The deintercalation reaction of the Li-GICs ceased after 6 weeks and only the residual compounds could be observed. A strong exothermic reaction was observed at 300 $^{\circ}C$ in thermal decomposition, and relatively stable decomposition curves were formed. A few endothermic curves have been observed at 1000 $^{\circ}C.$ After 6 weeks deintercalation reaction time of GICs, many exothermic and endothermic reactions were accompanied at the same time. In addition the reactions of the functional groups such as aromatic rings, nitrogen, $-CH_3$, $-CH_2$ etc. of GDIC obtained by the above reaction were confirmed by FT-IR spectrum. UV/VIS spectrophotometric measurement clearly shows the formation of a minimum energy value ($R_{min}$) for the compounds between Li-GICs as a starting material and Li-GDICs obtained until after 3 weeks of the deintercalation reaction, while they were no clear energy curves from 4 weeks of reaction time, because of the formation of the graphite structure, of high stages and of the Li compounds surrounding the graphite in the deintercalation reaction.

• Journal of the Korean Chemical Society
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• v.52 no.3
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• pp.303-314
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• 2008

The purpose of this study was to understand the experiment for measuring chemical reaction rate by precipitate formation and to develop experiments applying small-scale chemistry. For this study, the experimental method for measuring the effect of concentration and temperature on chemical reaction rates presented in the 10 high school science textbooks were classified by their experimental methods of confirming production. Subsequently, problems observed in carrying out the experiments for measuring chemical reaction rates by precipitate formation frequently presented in the 10 high school science textbooks were analyzed. Experiments applying small-scale chemistry were developed measuring chemical reaction rate by precipitate formation. According to the result of this study, there were some problems in the experimental method of precipitate formation for measuring chemical reaction rates presented in the high school science textbooks. Those problems in the science textbook experiments were insufficient specification of mixing methods of reaction solutions, obscurity of knowing when the character letter X disappeared, time delay in collecting the experimental data, formation of hazardous sulfur dioxide, uneasiness of fixing water bath container, controlling the reaction temperature, and low reproducibility. Those problems were solved by developing experiments applying smallscale chemistry. Presenting the procedure of mixing reaction solutions on the A4 reaction paper sheet made the experimental procedure clearly, using well plates and stem pipette shortened the reaction time and made it possible to continuously collect the experimental data. Furthermore, the quantity of hazardous sulfur dioxide was reduced 1/7 times and the time when the character letter X disappeared could be observed clearly. Since experiments for measuring the effect of concentration and temperature on chemical reaction rates could be performed in 30 minutes, the developing experiments applying SSC would help students understand the scientific concepts on the effect of concentration and temperature on chemical reaction rates with enough time for experimental data analysis and discussion.

• Korean Chemical Engineering Research
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• v.43 no.1
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• pp.125-128
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• 2005

Oil formation rate, composition of crude oil and formation of side products such as ${\alpha}-methyl$ styrene, ethyl benzene, benzene, toluene, dimer and trimer on thermal degradation of polystyrene were affected by various factors. Especially, formation of organic residue formed during reaction gave an important influence on formation of oil and composition of crude oil. Also, composition of formed crude oil showed a significant difference on reaction time. These results were caused by organic residue and carbonized solid formed during continuous reaction. Increase of residue and carbonized solid gave a decrease of yield of styrene and an increase of formation of ${\alpha}-methyl$ styrene, ethyl benzene, benzene, toluene. New reaction system was proposed for continuous operation at the thermal degradation of polystyrene.

• Journal of the Korean Society of Food Science and Nutrition
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• v.23 no.1
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• pp.137-142
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• 1994

The present paper was carried out to investigate the inhibition of carcinogenic N-nitrosodimethylamine(NDMA) formation by Maillard reactiion products and nondialyzable melanoidins, obtiane dfrom the glucoseamino acids(Lys, Gly, Arg, His) model systems under different pH conditions(pH 1.2, 4.2 and 6.0). Maillard raction products and nondialyzable melanoidins, produced from the 4 model systems, had a inhibitory action of N-nitrosodimethylamine formation. The inhibitiondegree by the nondialyzable mealanoidins. at pH 1.2 was similar to that at pH 4.2 and that by ascorbic acid at pH 1.2 . Inhibitory action of N-nitrosodimehylamine formation by the reduced Maillard reaction products and nondialyzable melanoidins were lower than that of original samples. Accordingly, it is assumed that the inhibition of N-nitrosodimehtylamine formation of Maillard reaction products is due to their reducing powers.

• Bulletin of the Korean Chemical Society
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• v.28 no.4
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• pp.529-532
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• 2007

Combined temperature programmed reaction (TPR) and infrared (IR) spectroscopic studies for Fischer- Tropsch reaction have been performed over Ru/SiO2 and Ru-Ag/SiO2 supported catalysts. Reaction of linearly absorbed CO with hydrogen starts at 375 K over Ru/SiO2 catalyst and reaches maximum at 420 K accompanied with an intensity decrease of linear CO absorption. The reaction with bridged absorbed CO peaks around 510-535 K. Addition of Ag yields mixed Ru-Ag bimetallic sites while it suppresses the formation of bridged bonded CO. Formation of methane on this modified surface occurs at 390 K and reaches maximum at 444 K. Suppression of hydrogen on the Ag-doped surface also occurs resulting in the formation of unsaturated hydrocarbons and of CHx intermediates not observed with Ru/SiO2 catalyst. Such intermediates are believed to be the building blocks of higher hydrocarbons during the Fischer-Tropsch synthesis. Linearly absorbed CO is found to be more reactive as compared to bridged CO. The Ag-modified surface also produces CO2 and carbon. On this surface, hydrogenation of CO begins at 390 K and reaches maximum at 494 K. The high temperature for hydrogenation of absorbed CO and C over Ru-Ag/SiO2 catalyst as compared to Ru/SiO2 catalyst is due to the formation of Ru-Ag bimetallic surfaces impeding hydrogen adsorption.