• Rapid Communication in Photoscience
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• v.4 no.2
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• pp.45-47
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• 2015

We have successfully synthesized $AgInS_2$ core and $AgInS_2$/ZnS core/shell nanoparticles by the sonochemical method. The ultrasonic based $AgInS_2$ and $AgInS_2$/ZnS nanoparticle synthesis can be utilized as a simple and rapid method. The $AgInS_2$/ZnS nanoparticles show the higher fluorescence intensity and quantum yield than $AgInS_2$ nanoparticles. Fluorescence wavelength of $AgInS_2$/ZnS shows blue shift from 635 nm to 610 nm against $AgInS_2$ because of reducing the defect sites and increasing spatial confinements. For the fluorescence lifetime, $AgInS_2$/ZnS (124.8 ns) has longer lifetime than $AgInS_2$ (54.8 ns).

• Journal of the Korean Ceramic Society
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• v.36 no.11
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• pp.1252-1260
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• 1999

The defect chemistry and electrical characteristics of the grain boundaries of semiconducting SrTiO3 ceramics synthesized with wet-chemically surface-coated powders were investigated. The starting powders were separated into groups of 1-10${\mu}{\textrm}{m}$ 10-20${\mu}{\textrm}{m}$ etc by sedimentation and sieving methods. Na+ ions were absorbed on the powder surfaces by wet chemical-treatment method. The width of the grain boundary ranged up to several nm and the intergranular materials was amorphous. The additives coated on the surface of the powders were observed to be present at the grain boundaries of the ceramics. The diffusion depth of the additives into grains was about 30nm for the SrTiO3 ceramics synthesized with 5w/o coated materials, The threshold voltage grain boundary resistance and boundary potential barrier of the ceramics increased from 0.67V/cm 2.27k$\Omega$ and 0.05eV to 80.9V/cm 13.0k$\Omega$ 1.44eV with increasing the amount of the additives from 0 to 5 w/o respectively .

• Corrosion Science and Technology
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• v.19 no.1
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• pp.8-15
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• 2020

In this paper, the efficiency and the inhibition mechanisms of cobalt salts (cobalt nitrate and cobalt-exchange silica Co/Si) for the corrosion protection of AA2024 were investigated in a neutral aqueous solution by using the electrochemical impedance spectroscopy (EIS) and polarization curves. The experimental measurements suggest that cobalt cation plays a role as a cathodic inhibitor. The efficiency of cobalt cation was important at the concentration range from 0.001 to 0.01 M. The formation of precipitates of oxides/hydroxides of cobalt on the surface at low inhibitor concentration was confirmed by the Scanning Electron Microscopy/Energy Dispersive X-Ray Spectroscopy (SEM/EDS) analysis. EIS measurements were also conducted for the AA2024 surface covered by water-based epoxy coating comprising Co/Si salt. The results obtained from exposure in the electrolyte demonstrated the improvement of the barrier and inhibition properties of the coating exposed in the electrolyte solution for a lengthy time. The SEM/EDS analysis in artificial scribes of the coating after salt spray testing revealed the release of cobalt cations in the coating defect to induce the barrier layer on the exposed AA2024 substrate.

• Bulletin of the Korean Chemical Society
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• v.15 no.8
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• pp.616-622
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• 1994

The oxidation of carbon monoxide by gaseous oxygen in the presence of a powdered $Nd_{1-x}Sr_xCoO_{3-y}$ solid solution as a catalyst has been investigated in the temperature range from 150$^{\circ}$C to 300$^{\circ}$C under various CO and $O_2$ partial pressures. The site of Sr substitution, nonstoichiometry, structure, and microstructure were studied by means of powder X-ray diffraction and infrared spectroscopy. The electrical conductivity of the solid solution has been measured at 300$^{\circ}$C under various CO and $O_2$ partial pressures. The oxidation rates have been correlated with 1.5-and 1.2-order kinetics with and without a $CO_2$ trap, respectively; first-and 0.7 order with respect to CO and 0.5-order to $O_2$. For the above reaction temperature range, the activation energy is in the range from 0.25 to 0.35 eV/mol. From the infrared spectroscopic, conductivity and kinetic data, CO appears essentially to be adsorbed on the lattice oxygens of the catalyst, while $O_2$ adsorbs as ions on the oxygen vacancies formed by Sr substitution. The oxygen vacancy mechanism of the CO oxidation and the main defect of $Nd_{1-x}Sr_xCoO_{3-y}$ solid solution are supported and suggested from the agreement between IR data, conductivities, and kinetic data.

• Journal of the Korean Chemical Society
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• v.28 no.4
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• pp.231-237
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• 1984

The x-values in the nonstoichiometric chemical formulas $YO_{1.5+x}\;and\;HoO_{1.5+x}$, have been measured in the temperature range from 700$^{\circ}$C to 1000$^{\circ}$C under oxygen pressures from $2{\times}l0^{-1}\;to\;1{\times}10^{-6}$ atm by gravimetric method. The observed x-values increase with increasing temperature and oxygen pressure. The enthalpies of formation of excess oxygen in yttrium oxide and holmium oxide decrease with decreasing oxygen pressure and are all positive values representing an endothermic process. The 1/n values calculated from the slopes of the plots of log x vs. log $P_{O2}$ increase with temperature and are positive values which means the higher oxygen pressure dependence at higher temperature. We have examined the nonstoichiometric defect and conduction mechanism from x-values and thermodynamic data.

• Journal of the Korean Chemical Society
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• v.36 no.1
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• pp.57-65
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• 1992

The method for investigating the retention behavior and separation optimization was studied to develop a reversed-phase liquid chromatography of eleven thiocarbamates that are used as herbicides. As an isocratic elution system, the statistical simplex technique was applied to find the optimum separation conditions. The resolution was quantitatively evaluated by using COF and ORM method. For thiocarbamate herbicides in which the elution order varies dramatically with solvent composition, the ORM method gave better result than the COF method. For the solvent composition of mobile phase in the ORM method, the ratio of methanol : acetonitrile : tetrahydrofuran : water was 16 : 29 : 2 : 53. Also in this research, an adjusted COF $(\overline{COF})$ method was proposed to rectify the defect in the current COF method, and the compositional ratio of mobile phase containing methanol : acetonitrile : water was 29.5 : 21.5 : 49.0 result of which is similar to that obtained by the ORM method.

• Journal of the Korean Chemical Society
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• v.39 no.9
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• pp.685-691
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• 1995

EHMACC and EHPC programs written in VAX version to calculate the tight-binding extended Huckel method is converted into the micro-soft fortran available to PC. The band calculation of LaNiO3 unit cell and extended ($2{\times}2{\times}1$) cell with perovskite structure is made by the PC/386 and PC/486. The calculation is also made for the DOS and the COOP. It is supposed that the electronic property of $LaNiO_3$ is semiconductor along to the ${\Gamma}{\rightarrow}H,\;H{\rightarrow}N,\;and\;N{\rightarrow}{\Gamma}(2D)$ direction with band gap about 0u.35 eV, while metal property in ${\Gamma}{\rightarrow}P\;and\;P{\rightarrow}N(3D)$ direction. The oxygen atom property in $LaNiO_3$ is more effectively affected by oxygen atom position than defect of nickel atom.

• Bulletin of the Korean Chemical Society
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• v.33 no.3
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• pp.809-817
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• 2012

The resonance structure of the preionization spectrum of $H_2$ in the region immediately above its ionization threshold, ($^2{\sum}_{g}^{+}$, $\nu^+=0$, $N^+=0$) converging toward its rotationally excited ($\nu^+=0$, $N^+=2$) limit, is complicated due to perturbation by the vibrationally excited levels $7_{p\pi}\;v=1$ and $57_{p\pi}\;v=2$. The spectra of interlopers are separated from the rotationally preionizing Rydberg series to allow analysis of this complex resonance structure. Although only two vibrationally excited levels perturb the rotational preionization spectrum, at least 6 interloper Rydberg series participate in the complex spectrum over most of its energy range and more interloper series participate at a narrow range around $124500cm^{-1}$ in the spectrum. To allow handling of an arbitrary number of interloper series, MATLAB$^{(R)}$'s symbolic operation is used to perform on-the-fly formulation.

• Journal of the Korean Ceramic Society
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• v.34 no.12
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• pp.1221-1226
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• 1997

The effects of sintering atmosphere and dopant addition on the behavior of densification and grain growth of SnO2 ceramics were investigated with consideration of defect chemistry. CoO and Nb2O5 were chosen as dopants, and oxygen and nitrogen were used for controlling of sintering atmospheres. With the decrease of oxygen partial pressure, densification was depressed due to evaporation of SnO2 ceramics. In the case of SnO2 sintering, the addition of CoO, which produced oxygen vacancy in SnO2 ceramics, led to acceleration of densification and grain growth. On the contrary, when Nb2O5 as a dopant producing Sn vacancy was added to SnO2 ceramics, densification and grain growth were simultaneously retarded. As results, it was conformed that diffusion of oxygen ions was rate determinant in densification and grain growth of SnO2 ceramics.

• The Korean Journal of Ceramics
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• v.4 no.2
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• pp.128-135
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• 1998

The paper gives a brief introduction to protonic defects and their chemistry, thermodynamics and transport in oxides. The temperature dependence of the equilibrium concentration of protons is illustrated and compared for different acceptor-doped oxides. The difficulties of saturating as well as emptying the oxides of protons are discussed. In order to illustrate the possibility of lattice relaxation of defects, a conceptual study is made of a case where the enthalpy of dissolution of protons(water) at the cost of oxygen vacancies is assumed dependent on the concentration of vacancies. It is shown how this changes the behavior of hydration curves vs temperature and water vapour pressure. finally, a discussion is given on the water uptake in heavily oxygen deficient oxides; how water uptake may affect order-disorder in the oxygen sublattice and eventually lead to defective, disordered or ordered oxyhydroxides or hydroxides of potential interest as intermediate temperature proton conductions.