• Nuclear Engineering and Technology
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• v.52 no.5
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• pp.1013-1021
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• 2020

A combination of simultaneous thermal analysis, evolved gas analysis and non-ambient XRD techniques was used to characterise and investigate the conversion reactions of ammonium uranates into uranium oxides. Two solid phases of the ternary system NH₃ - UO₃ - H₂O were synthesised under specified conditions. Microspheres prepared by the sol-gel method via internal gelation were identified as 3UO₃·2NH₃·4H₂O, whereas the product of a typical ammonium diuranate precipitation reaction was associated to the composition 3UO₃·NH₃·5H₂O. The thermal decomposition profile of both compounds in air feature distinct reaction steps towards the conversion to U₃O₈, owing to the successive release of water and ammonia molecules. Both compounds are converted into α-U₃O₈ above 550 ℃, but the crystallographic transition occurs differently. In compound 3UO₃·NH₃·5H₂O (ADU) the transformation occurs via the crystalline β-UO₃ phase, whereas in compound 3UO₃·2NH₃·4H₂O (microspheres) an amorphous UO₃ intermediate was observed. The new insights obtained on these uranate systems improve the information base for designing and synthesising minor actinide-containing target materials in future applications.

• Journal of the Korean Magnetics Society
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• v.14 no.5
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• pp.180-185
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• 2004

The electromagnetic properties and microstructures of the basic composition of (Ni$\sub$0.2/Cu$\sub$0.1/Zn$\sub$0.2/)$\sub$0.5/ (Fe$_2$O$_3$)$\sub$0.5/ were invested by changing of SO$_4$, Cl and NO$_3$ series. We were prepared by coprecipitation method and sintered at temperatures 950$^{\circ}C$, 1150$^{\circ}C$, l350$^{\circ}C$, respectively. When sintering at temperature 950$^{\circ}C$, Cl and NO$_3$ series became perfection sintering. On the other hand, SO$_4$ series showed perfection sintering at temperature 1150$^{\circ}C$. According to particle size analysis result, higher magnetic permeability and magnetization value were observed by Cl series than SO$_4$ or NO$_3$ series.

• Applied Chemistry for Engineering
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• v.24 no.6
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• pp.599-604
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• 2013

In this study, Ti added Mn-Cu mixed oxide catalysts were prepared by a co-precipitation method and used for the low temperature (< $200^{\circ}C$) selective catalytic reduction (SCR) of NOx with $NH_3$. Physicochemical properties of these catalysts were characterized by BET, XRD, XPS, and TPD. Mn-Cu mixed oxide catalysts were found to be amorphous with a large surface and they showed high SCR activity. Experimental results showed that the addition of $TiO_2$ to Mn-Cu oxide enhanced the SCR activity and $N_2$ selectivity. Ti addition led to the chemically adsorbed oxygen species that promoted the oxidation of NO to $NO_2$ and increased the number of $NH_3$ adsorbed-sites such as $Mn^{3+}$.

• BMB Reports
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• v.33 no.2
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• pp.172-178
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• 2000

The lipoxygenase was purified 35 fold to homogeneity from the Korean red potato by an ammonium sulfate precipitation and DEAE-cellulose column chromatography. The simple purification method is useful for the preparation of pure lipoxygenase. The molecular weight of the enzyme was estimated to be 38,000 by SDS-polyacrylamide gel electrophoreses and Sepharose 6B column chromatography. The purified enzyme with 2 M $(NH_4)_2SO_4$ in a potassium phosphate buffer, pH 7.0, was very stable for 5 months at $-20^{\circ}C$. Because the purified lipoxygenase is very stable, it could be useful for the screening of a lipoxygenase inhibitor. The optimal pH and temperature for lipoxygenase purified from the red potato were found to be pH 9.0. and $30^{\circ}C$, respectively. The Km and Vmax values for linoleic acid of the lipoxygenase purified from the red potato were $48\;{\mu}M$ and $0.03\;{\mu}M$ per minute per milligram of protein, respectively. The enzyme was insensitive to the metal chelating agents tested (2 mM KCN, 1 and 10mM EDTA, and 1 mM $NaN_3$), but was inhibited by several divalent cations, such as $Cu^{++}$, $Co^{++}$ and $Ni^{++}$. The essential amino acids that were involved in the catalytic mechanism of the 5-lipoxygenase from the Korean red potato were determined by chemical modification studies. The catalytic activity of lipoxygenase from the red potato was seriously reduced after treatment with a diethylpyrocarbonate (DEPC) modifying histidine residue and Woodward's reagent (WRK) modifying aspartic/glutamic acid. The inactivation reaction of DEPC (WRK) processed in the form of pseudo-first-order kinetics. The double-logarithmic plot of the observed pseudo-first-order rate constant against the modifier concentration yielded a reaction order 2, indicating that two histidine residues (carboxylic acids) were essential for the lipoxygenase activity from the red potato. The linoleic acid protected the enzyme against inactivation by DEPC(WRK), revealing that histidine and carboxylic amino acids residues were present at the substrate binding site of the enzyme molecules.

• Transactions of the Korean hydrogen and new energy society
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• v.19 no.6
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• pp.514-519
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• 2008

In the present study, biomass pyrolysis was done using five different kinds of catalysts with change in the support species and their compositions. Ni was loaded on alumina, ceria and alumina-ceria supports using co-precipitation method. In all the catalysts, 30wt% of nickel was loaded on the support materials. The paper used in daily writing purposes was taken into account as biomass sample. In the experiment, 19 of biomass was mixed with o.1g of each catalyst separately. Thermogravimetric analysis (TGA) was performed with all the catalysts diminished the initial degradation temperature of paper biomass sample considerably. During the pyrolysis process, the temperature was raised from room temperature to $800^{\circ}C$ with the heating rate of $10^{\circ}C$/min in the furnace. The cumulative $H_2$ volume had reached the best value of l4.02ml with the Ni/$Al_2O_3-CeO_2$ 30wt%/(50wt%-50wt%) catalysts. In presence of all the catalysts, the highest amount of $H_2$ was produced at $800^{\circ}C$, 10min. of residence time.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.109-109
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• 2010

$Er^{3+}$ ion shows a stable and efficient luminescence at 1.54mm due to its $^4I_{13/2}\;{\rightarrow}\;^4I_{15/2}$ intra-4f transition. As this corresponds to the low-loss window of silica-based optical fibers, Er-based light sources have become a mainstay of the long-distance telecom. In most telecom applications, $Er^{3+}$ ions are excited via resonant optical pumping. However, if nanocluster-Si (nc-Si) are co-doped with $Er^{3+}$, $Er^{3+}$ can be excited via energy transfer from excited electrical carriers in the nc-Si as well. This combines the broad, strong absorption band of nc-Si with narrow, stable emission spectra of $Er^{3+}$ to allow top-pumping with off-resonant, low-cost broadband light sources as well as electrical pumping. A widely used method to achieve nc-Si sensitization of $Er^{3+}$ is high-temperature annealing of Er-doped, non-stoichiometric amorphous thin film with excess Si (e.g.,silicon-rich silicon oxide(SRSO)) to precipitate nc-Si and optically activate $Er^{3+}$ at the same time. Unfortunately, such precipitation and growth of nc-Si into Er-doped oxide matrix can lead to $Er^{3+}$ clustering away from nc-Si at anneal temperatures much lower than ${\sim}1000^{\circ}C$ that is necessary for full optical activation of $Er^{3+}$ in $SiO_2$. Recently, silicon-rich silicon nitride (SRSN) was reported to be a promising alternative to SRSO that can overcome this problem of Er clustering. But as nc-Si formation and optical activation $Er^{3+}$ remain linked in Er-doped SRSN, it is not clear which mechanism is responsible for the observed improvement. In this paper, we report on investigating the effect of separating the nc-Si formation and $Er^{3+}$ activation by using hetero-multilayers that consist of nm-thin SRSO or SRSN sensitizing layers with Er-doped $SiO_2$ or $Si_3N_4$ luminescing layers.

• Journal of the Korean Physical Society
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• v.73 no.10
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• pp.1437-1443
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• 2018

In this work, $SnO_2$ modified with reduced graphene oxide (rGO) and carbon nanotubes (CNTs) separately and combined sensitized by using the co-precipitation method and their sensing behavior toward ethanol vapor at room temperature were investigated. An interdigitated electrode (IDE) gold substrate is very expensive compared to a fluorine doped tin oxide (FTO) substrate; hence, we used the latter to reduce the fabrication cost. The structure and the morphology of the studied materials were characterized by using differential thermal analyses (DTA) and thermogravimetric analysis (TGA), transmission electron microscope (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller surface area and Barrett-Joyner-Halenda (BJH) pore size measurements. The studied composites were subjected to ethanol in its gas phase at concentrations from 10 to 200 ppm. The present composites showed high-performance sensitivity for many reasons: the incorporation of $SnO_2$ and CNTs which prevents the agglomeration of rGO sheets, the formation of a 3D mesopourus structure and an increase in the surface area. The decoration with rGO and CNTs led to more active sites, such as vacancies, which increased the adsorption of ethanol gas. In addition, the mesopore structure and the nano size of the $SnO_2$ particles allowed an efficient diffusion of gases to the active sites. Based on these results, the present composites should be considered as efficient and low-cost sensors for alcohol.

• Clean Technology
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• v.21 no.3
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• pp.200-206
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• 2015

In order to investigate the effect of cerium oxide addition, Cu-ZnO-CeO₂ catalysts were prepared using co-precipitation method for water gas shift (WGS) reaction. A series of Cu-ZnO-CeO₂ catalyst with fixed Cu Content (50 wt%, calculated as CuO) and a given ceria content (e.g., 0, 5, 10, 20, 30, 40 wt%, calculated as CeO₂) were tested for catalytic activity at a GHSV of 95,541 h^-1, and a temperature range of 200 to 400 ℃. Cu-ZnO-CeO₂ catalysts were characterized by using BET, SEM, XRD, H₂-TPR, and XPS analysis. Varying composition of Cu-ZnO-CeO₂ catlysts led the difference characteristics such as Cu dispersion, and binding energy. The optimum 10 wt% doping of cerium facilitated catalyst reduction at lower temperature and improved the catalyst performance greatly in terms of CO conversion. Cerium oxide added catalyst showed enhanced activities at higher temperature when it compared with the catalyst without cerium oxide. Consequently, ceria addition of optimal composition leads to enhanced catalytic activity which is attributed to enhanced Cu dispersion, lower binding energy, and hindered Cu metal agglomeration.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.167-167
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• 2003

현대 산업이 발전함에 따라 전자부품의 초소형화, 고성능화가 요구되어지고 있으며, 이러한 점에 부응하기 위하여 Pottier 효과를 이용하여 국부냉각이 가능한 열전재료에 대한 많은 연구가 이루어지고 있다. 열전재료에는 사용온도 영역에 따라 여러 종류가 있지만, Bi-Te계 열전재료는 상온영역에서 가장 성능지수(Z=$\alpha$$^2$$\sigma$/$textsc{k}$, $\alpha$는 Seebeck 계수, $\sigma$는 전기전도도, $textsc{k}$는 열전도도)가 높아 각종 냉각소자로서 사용되어 지고 있다. 하지만, 초소형 전자부품의 국부냉각을 위해서는 성능지수의 향상, 특히, 저온 영역에서의 성능지수의 향상이 요구되고 있다. 본 연구에서는 Bi-Te계 열전재료의 성능지수를 향상시키기 위하여, 열전도도의 저하에 의한 성능지수의 향상을 연구목적으로 하였다 열전도도는 전자에 의한 열전도도(K$_{e}$)와 phonon에 의한 열전도도(K$_{p}$)로 이루어지며, 전기전도도에 큰 영향을 미치지 않는 결정립 사이즈영역에서 결정립의 크기를 미세화 하면, 결정입계에서의 phonon의 산란이 증가하여 phonon에 의한 열전도도를 저하시킴으로서 성능지수의 향상이 기대된다. 따라서 본 연구에서는 나노사이즈 분말의 제조에 많이 이용되며 입자크기의 조절이 용이한 공침법을 이용하여 Bi-Te계 열전재료 분말을 제조하고 열전재료에의 적용가능성을 검토하였다.

• Corrosion Science and Technology
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• v.19 no.2
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• pp.82-88
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• 2020

This work examined the corrosion protection performance of benzoate loaded hydrotalcite/graphene oxide (HT/GO-BZ) for carbon steel. HT/GO-BZ was fabricated by the co-precipitation method and characterized by infrared spectroscopy, X-ray diffraction, and scanning electronic microscopy. The corrosion inhibition action of HT/GO-BZ on carbon steel in 0.1 M NaCl solution was evaluated by electrochemical measurements. The benzoate content in HT/GO-BZ was determined by UV-Vis spectroscopy. Subsequently, the effect of HT/GO-BZ on the corrosion resistance of the water-based epoxy coating was investigated by the salt spray test. The obtained results demonstrated the intercalation of benzoate and GO in the hydrotalcite structure. The benzoate content in HT/GO-BZ was about 16%. The polarization curves of the carbon steel electrode revealed anodic corrosion inhibition activity of HT/GO-BZ and the inhibition efficiency was about 95.2% at a concentration of 3g/L. The GO present in HT/GO-BZ enhanced the inhibition effect of HT-BZ. The presence of HT/GO-BZ improved the corrosion resistance of the waterborne epoxy coating.