• Bulletin of the Korean Chemical Society
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• v.10 no.1
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• pp.30-32
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• 1989

Traces of nine elements, gold, arsenic, cobalt, chromium, copper, europium, hafnium, sodium and antimony in commercially available silicon crystals were determined by the instrumental neutron activation analysis using the single comparator method. The values of the concentrations of these elements in both single and polycrystals were found to decrease significantly to a low limiting level by simply washing and etching surface contaminants having been introduced during various steps of sample preparation and irradiation. However, the chromium levels in polycrystals were not easily decreased, these depending upon the cutting tools employed. The Sb-doped content in each semiconductor has been compared with the associated quantities such as the concentration and the conductivity range given by the sample donor. Uncertainty in the sodium analysis due to the fission neutron reaction by silicon itself was discussed.

• Bulletin of the Korean Chemical Society
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• v.7 no.1
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• pp.6-12
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• 1986

Overlap integrals for the case in which the ground and excited states are represented by Morse potential functions were derived. In order to calculate the spectral intensities in Morse wavefunctions, a method of expanding the wavefunctions of one state in terms of the other was developed to allow the ground and the excited state frequencies to be different. From the expansion of Morse wavefunctions, recursion formulas were developed for variational matrix elements of Morse wavefunctions. The matrix elements can be calculated using these recursion formulas and the diagonalized results which eigenvalues (allowed energies) were all successfully satisfied to Morse energy formulas.

• Bulletin of the Korean Chemical Society
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• v.19 no.1
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• pp.50-56
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• 1998

A solvent sublation was studied for the determination of trace Cd, Co, Cu and Ni in water samples. Ammonium pyrrolidine dithiocarbamate (APDC) was used as a complexing agent. Experimental conditions such as pH of solution, amounts of APDC, the type and amount of surfactant, the type of solvent, etc. were optimized for the effective sublation of analytes. After metal-PDC complexes were formed in sample solutions of pH 2.5, the precipitate-type complexes were floated in a flotation cell with an aid of sodium lauryl sulfate as a surfactant and by bubbling with nitrogen gas. The precipitates were dissolved and separated into the surface layer of methyl iso-butyl ketone (MIBK). The analytes preconcentrated were determined by a graphite furnace atomic absorption spectrophotometry (GF-AAS). Extractability of each element was 88% for Cd(Ⅱ), 86% for Co(Ⅱ), 95% for Cu(Ⅱ) and 76% for Ni(Ⅱ), respectively. And this procedure was applied to the analysis of real samples. From the recoveries of more than 92%, it was concluded that this method could be simple and applicable for the determination of trace elements in various water samples of a large volume.

• Bulletin of the Korean Chemical Society
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• v.4 no.2
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• pp.87-91
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• 1983

Molecular dynamic method has been applied to a single polymer chain immersed in a solvent. The interactions for the pairs, of two solvent molecules (SS), of a chain element and a solvent molecules (CS), and of two non-neighbor chain elements (CC) are given by the Lennard-Jones potential, and the interaction between two bonded chain elements is given by a harmonic potential. We changed the CS interaction parameter ${\varepsilon}_{CS}$ to 0.5, 1.0 and 2.0 times of the SS interaction ${\varepsilon}_{SS}$. We calculated the pair correlation functions for the SS, CS, and CC pairs, end-to-end distance and radius of gyration with the varying ${\varepsilon}_{CS}$ parameters. The results showed that a phase separation occurs between the polymer and solvent in the 0.5 system where ${\varepsilon}_{CS}$ = 0.5 {\varepsilon}_{SS}$. The autocorrelation functions for end-to-end distance and radius of gyration were also calculated.

• Bulletin of the Korean Chemical Society
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• v.13 no.4
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• pp.413-419
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• 1992

The theoretical equation for the relaxation spectrum of nonlinear viscoelastic polymeric material was derived from the Ree-Eyring and Maxwell non-Newtonian model. This model consists of infinite number of hyperbolic sine law Maxwell elements coupled in parallel plus a spring without a dashpot. Infinite number of nonlinear viscoelastic Maxwell elements can be used by specifying distribution of relaxation times, hole volumes, molecular weights, crystallite size and conformational size, etc. The experimentals of stress relaxation were carried out using the tensile tester with the solvent chamber. The relaxation spectra of nylon 6 filament fibers in various electrolytic solutions were obtained by applying the experimental stress relaxation curves to the theoretical equation of relaxation spectrum. The determination of relaxation spectra was performed from computer calculation.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.11 no.1
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• pp.23-29
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• 2013

LCC (Liquid cadmium cathode) is used for electrowinning in pyroprocessing to recover uranium and transuranic elements simultaneously. It is one of the core technologies in pyroprocessing with higher proliferation resistance than a wet reprocessing because LCC-cell does not separate TRU from uranium. The crucible which holds the LCC is technically important because it should be nonconducting material to prevent deposition of metallic elements on the crucible outer surface. The chemical stability is also crucial factor to choose crucible material due to the strong reactivities of TRU and possible incorporation of Li metal during the operation. In this study, the chemical stabilities of four kinds of representative ceramic materials such as $Al_2O_3$, MgO, $Yl_2O_3$ and BeO were thermodynamically and experimentally evaluated at $500^{\circ}C$ with simulated LCC. The contact angle of LCC on ceramic materials was measured as function of time to predict chemical reactivity. $All_2O_3$ showed poorest chemical stability and the pores in BeO contributed to a decreases in contact angle. MgO and $Y_2O_3$ have superior chemical stability among the materials.

• Nuclear Engineering and Technology
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• v.54 no.7
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• pp.2427-2434
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• 2022

Series of unequal quantity Nd/Ce co-doped ceramic nuclear waste forms, (Gd, Nd)₂(Zr, Ce)₂O₇, were prepared to tailor its ordered pyrochlore or disordered fluorite structure. The phase transition, microtopography, and elemental composition of the ceramic samples were systematically investigated, especially the effect of order-disorder structure on the chemical stability. It was confirmed that unequal quantity of Nd/Ce could synchronously replace the Gd/Zr-sites of Gd₂Zr₂O₇. And the phase transition of order-disorder structure could be successfully tailored by regulating the average cationic radius ratio of (Gd, Nd)₂(Zr, Ce)₂O₇ series. The elements of Gd, Nd, Zr, and Ce are uniformly distributed in the ordered or disordered structures. The MCC-1 leaching results showed that (Gd, Nd)₂(Zr, Ce)₂O₇ pyrochlore ceramic nuclear waste forms had excellent chemical stability, whose elements' normalized leaching rates were as low as 10^-4-10^-7 g·m^-2·d^-1 after 7 days. In particular, the chemical stability of disordered structure was superior to that of ordered structure. It was proposed that the force constant and the closest packing were changed with the structure transformation resulting the chemical stability difference.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.118.1-118.1
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• 2014

Stars create and expel new chemical elements and dust at the end of the stellar life cycle. Therefore, understanding the evolved stars, their mass loss process, and the conditions of the returning material to be mixed with the surrounding interstellar medium is an important step toward studies on the new generation of stars as well as the evolution of cosmic elements in galactic scale. I will review the first results from the ALMA Early Science on the evolved stars and direct future works.

• Journal of the Mineralogical Society of Korea
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• v.11 no.1
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• pp.20-31
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• 1998

Adsorption of metal elements onto illite and halloysite was investigated at $25^{\circ}C$ using pollutant water collected from the gold-bearing metal mine. Incipient solution of pH 3.19 was reacted with clay minerals as a function of time: 10 minute, 30 minute, 1 hour, 12 hour, 24 hour, 1 day, 2 day, 1 week, and 2 week. Twenty-seven cations and six anions from solutions were analyzed by AAs (atomic absorption spectrometer), ICP(induced-coupled plasma), and IC (ion chromatography). Speciation and saturation index of solutions were calculated by WATEQ4F and MINTEQA2 codes, indicating that most of metal ions exist as free ions and that there is little difference in chemical species and relative abundances between initial solution and reacted solutions. The adsorption results showed that the adsorption extent of elements varies depending on mineral types and reaction time. As for illite, adsorption after 1 hour-reaction occurs in the order of As>Pb>Ge>Li>Co, Pb, Cr, Ba>Cs for trace elements and Fe>K>Na>Mn>Al>Ca>Si for major elements, respectively. As for halloysite, adsorption after 1 hour-reaction occurs in the order of Cu>Pb>Li>Ge>Cr>Zn>As>Ba>Ti>Cd>Co for trace elements and Fe>K>Mn>Ca>Al>Na>Si for major elements, respectively. After 2 week-reaction, the adsorption occurs in the order of Cu>As>Zn>Li>Ge>Co>Ti>Ba>Ni>Pb>Cr>Cd>Se for trace elements and Fe>K>Mn>Al, Mg>Ca>Na, Si for major elements, respectively. No significant adsorption as well as selectivity was found for anions. Although halloysite has a 1:1 layer structure, its capacity of adsorption is greater than that of illite with 2:1 structure, probably due to its peculiar mineralogical characteristics. According to FTIR (Fourier transform infrared spectroscopy) results, there was no shift in the OH-stretching bond for illite, but the ν1 bond at 3695 cm-1 for halloysite was found to be stronger. In the viewpoint of adsorption, illite is characterized by an inner-sphere complex, whereas halloysite by an outer-sphere complex, respectively. Initial ion activity and dissociation constant of metal elements are regarded as the main factors that control the adsorption behaviors in a natural system containing multicomponents at the acidic condition.

• Applied Chemistry for Engineering
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• v.20 no.4
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• pp.449-452
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• 2009

The absence of Fe, Se, and Mo in a minimal medium prevented the production of hydrogen from the anaerobic culture of Escherichia coli MC4100. Fe, Se, and Mo are known to be cofactors of formate dehydrogenase ($FDH_{II}$) of both E. coli and Enterobacter aerogenes. Hence when these trace elements are absent in the minimal medium, hydrogen production through formate dehydrogenation would be inhibited not only in E. coli but also in E. aerogenes. Hydrogen production by E. aerogenes 413 was delayed when lacking these trace elements. Therefore, it is believed that hydrogen production of E. aerogenes is initiated not by the reoxidation of nicotinamide adenine dinucleotide (NADH) but by formate decarboxylation.