• 대한화학회지
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• 제29권5호
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• pp.478-481
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• 1985

염화 알칸술포닐과 파라 치환된 아닐린간의 친핵성 치환반응을 메탄올-아세토니트릴 혼합용매하에서 연구하였다. 기질의 반응성, 친핵체의 치환기효과 및 용매효과로 부터 반응 메카니즘이 $S_N2$임을 알았다. i-PSC의 경우 메탄올 조성이 커짐에 따라 전이상태가 더 loose해 짐을 알았다.

• Bulletin of the Korean Chemical Society
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• 제32권9호
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• pp.3267-3273
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• 2011

Ag(I) carboxylate gelators with mixed-ligands were systemically investigated to understand the mechanism of the organic gel formation. The gelators constructed 3-D networks of nanometer-sized thin fibers which facilitated gel formation in various aromatic organic solvents, even at very low concentrations. The loss of reflection peaks in the X-ray diffraction data indicated the reduction of strong interactions between the long alkyl chains as the Ag(I) carboxylates formed gels by maximizing their interactions with the organic solvents. The gelation temperature ($T_{gel}$) was measured to explore the interaction between the gelator molecules and solvents depending on their composition and concentration. Based on the gelation phenomena, a dissociation/re-association mechanism was proposed.

• 한국세라믹학회지
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• 제37권1호
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• pp.33-43
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• 2000

Up-conversion of rare-earth element added glass is promising area for short wavelength laser source by utilizing high power semiconductor infra-red laser if the efficiency can be increased by proper method. In this study, relatively low phonon energy fluoride glasses were prepared by co-doping rare-earth elements to realize the high efficiency up-convertor. The physical, chemical, andoptical properties of co-doped fluoride glasses were measured. 10 combinations of 5 different rare-earth fluoride elements doped samples were prepared and their transition temperatures, chemical durability, density, hardness, refractive index, absorption, fluorescence, and fluorescence lifetime were measured. 480nm wavelengths blue up-conversion was found in the Yb3+/Tm3+ co-doped glass sample with 800nm laser source and the optimum composition for the most efficient blue up-conversion was found from the glass sample with 0.3 mol% TmF3 and 1 mol% YbF3.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 추계학술대회 논문집 학회본부
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• pp.475-479
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• 1996

At present studies, we are going to suggest the new type of Perovskite derived catalysts which modify the defects of transition metals impregnated. Perovskite type catalyst is a typical mixed metal oxides, and there are "defect"s (from like that oxygen, cation, crystallic structure) were made by difference from composition, preparing method and so forth. And because this, its electro-magnetic character could be much changed. By using this phenomena, it could utilize the modification of adsorption/desorption characters as well as the catalytic activities in NOx reduction. Because perovskite type catalyst can exchange the metal of the each lattice site freely and it is possible to represent the peculiar.

• Bulletin of the Korean Chemical Society
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• 제20권5호
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• pp.517-524
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• 1999

By heating the magnesiumsilicate (Mg2SiO4:forsterite) xerogel in carbon dioxide, carbonaceous component was intentionally introduced into the amorphous solid precursor. Carbon was introduced homogeneously as unidentate carbonate. Upon being heated at 800 。C in carbon dioxide, the xerogel which had homogeneously distributed carbonaceous component in it crystallized into a single phase product of a new crystalline material, which had approximate composition of Mg8Si4Ol8C. The powder X-ray diffraction pattern of the new crystalline material did not match with any known crystalline compound registered in the powder diffraction file. Crystallization from amorphous xeroget to the new crystalline phase occurred in a very narrow range of temperature, from 750 。C to 850 。C in carbon dioxide, or in dty oxygen. Upon being heated above 850 。C, carbonaceous component was expelled from the product, accompanied by irreversible transition from the new crystalline material to forsterite.

• Bulletin of the Korean Chemical Society
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• 제20권12호
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• pp.1451-1456
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• 1999

Solvolyses of α-methoxy-α-(trifluoromethyl)phenylacetyl chloride in H₂O, D₂O, CH₃OD, 50% D₂O-CH₃OD, and in aqueous binary mixtures of acetone, dioxane, ethanol and methanol are investigated at 25.0℃. The Grunwald-Winstein plots of first-order rate constants for α-methoxy- α-(trifluoromethyl)phenylacetyl chloride with $Y_{Cl}$ show a dispersion phenomenon. Solvent nucleophilicity N has been shown to give considerable im-provement when it is added as an 1N term to the original Grunwald-Winstein for the solvolyses of α-methoxy- α-(trifluoromethyl)phenylacetyl chloride. The dispersions in the Grunwald-Winstein correlations in the present studies are caused by solvent nucleophilicity. The magnitude of l and m values associated with a change of solvent composition predicts the associative $S_N2$ transition state. The kinetic solvent isotope effects determined in deuterated water and methanol are consistent with the proposed mechanism of the general base catalyzed associative $S_N2$ or $S_AN$ mechanism for the of α-methoxy- α-(trifluoromethyl)phenylacetyl chloride.

• Bulletin of the Korean Chemical Society
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• 제13권6호
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• pp.642-647
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• 1992

Second-order rate constants have been measured spectrophotometrically for the reactions of substituted phenyl acetates with butane-2,3-dione monoximate and p-chlorophenoxide anions in MeCN-H$_2$O mixtures of varying compositions. The reaction rate, unexpectedly, decreased remarkably upon initial additions of MeCN to H$_2$O up to 30-40 mole ${\%}$ MeCN, and followed by a gradual increase upon further additions of MeCN. The change in solvent composition also influenced the magnitude of the ${\alpha}$-effect, i.e., the ${\alpha}$-effect increased as the mole ${\%}$ MeCN increased. The solvent dependent ${\alpha}$-effect for the present system appears to indicate that the differential solvation between the ${\alpha}$-effect nucleophile and the corresponding normal nucleophile is not solely responsible but the difference in the transition-state stabilization is also responsible for the ${\alpha}$ -effect in organic solvent-rich region.

• Bulletin of the Korean Chemical Society
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• 제6권5호
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• pp.259-263
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• 1985

Rate Constants for the solvolysis of p-methylbenzyl chloride in various ethanol-water mixtures were studied at 30 and $40^{\circ}C$ under various pressures up to 1600 bar. The 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 (${\Delta}V^{\neq},{\Delta}{\beta}^{\neq},{\Delta}H^{\neq}\;and\;{\Delta}S^{\neq}$) were evaluated. The values of ${\Delta}V^{\neq}\;and\;{\Delta}{\beta}^{\neq}$ exhibit the extremum behavior at about 0.30 mole fraction of ethanol. This behavior is discussed in terms of solvent structure variation (electrostriction). From the relation between the reaction rate and the dielectric constant of solvent or the number of water molecule participated in the transition state, it could be postulated that the reaction proceeds through $S_N1$ mechanism.

• Bulletin of the Korean Chemical Society
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• 제9권5호
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• pp.283-288
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• 1988

The titled properties on reduction of the perovskite $LaBO_3$ (B = Fe, Co, Ni) have been investigated by means of temperature-programmed reduction, isothermal reduction and X-ray diffraction methods. Nominal composition of $LaFeO_{3.18},\;LaCoO_{3.00}\;and\;LaNiO_{2.92}$ are determined. Reduction reaction of these mixed oxides differed according to B-site transition metal and thermal stability on reduction decreased as following order: $LaFeO_{3.18}$ > $LaCoO_{3.00}$ > $LaNiO_{2.92}$. From the results of isothermal reaction, kinetics on reduction of the perovskite has been discussed in detail.

• 접착 및 계면
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• 제12권1호
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• pp.16-25
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• 2011

Core 입자로 methyl methacrylate (MMA), n-butyl methacrylate (BMA)를 하고 shell 입자로 MMA, BMA, stylene (St), 2-hydroxylethylmethacrylate (2-HEMA), acrylic acid (AA)를 각각 사용하여 개시제 aommonium persulfate (APS), 유화제로 sodium dodecyl benzene sulfonate (SDBS)의 농도(0.01~0.03 wt%), 단량체의 종류와 조성을 변화시켜 수용성 유화중합으로 다중 core-shell 복합입자를 제조하여 전화율, 입자경 및 입도 분포, 평균 분자량, 분자구조, 유리전이온도, 입자의 형태 및 인장강도와 신율을 각각 측정하여 다음과 같은 결론을 얻었다. SDBS 농도 0.02 wt%에서 MMA core-(BMA/St/AA) shell 복합인자가 전화율이 98%로 우수하였고, 입자 직경은 SDBS 농도 0.03 wt%에서 BMA core-(MMA/St/AA) shell의 복합입자가 $0.47{\mu}m$로 높게 나왔다. 유리전이온도 측정은 단일 core-shell 복합입자의 2군데에 비하여 다중 core-shell 복합입자는 3군데가 존재하여 shell단량체 내의 단량체의 종류와 조성에 따라 유리전이온도 조절도 가능하고 동시에 접착력이 향상된 접착소재로서 부직포 섬유 결속제로 사용될 수 있었다.