• Bulletin of the Korean Chemical Society
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• v.33 no.2
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• pp.524-528
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• 2012

A kind of nanosized sulfated zirconia was prepared by a hydrothermal method, and full characterized by XRD, TEM, BET, TGA, and FTIR. Its catalytic activity was evaluated in the esterification reactions, including the testing of the catalytic reusability and the optimization of reaction conditions. The obtained catalyst was revealed to be highly efficient solid catalyst for the esterification of acetic acid with n-butanol, presenting the advantages of high conversion and selectivity, easy recovery, and steady reusability.

• Journal of the Korean Ceramic Society
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• v.31 no.2
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• pp.117-128
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• 1994

Hematite particles were obtained by hydrothermal reaction of ferric hydroxide in the presence of small amount of citric acid which is acted as crystal growth controller. The effects of hydrothermal reaction condition son the morphology and crystal structure of powder were investigated using X-ray, TEM and FT-IR. Ellipsoidal or rectangular hematite particles were formed in the range of pH 10.75~11.75 as initial basicity of reactants and 3$\times$10-5 ~9$\times$10-5 mol as citric acid content. Crystallization of hematite was inhibited in the range of pH9. 0~10.5 and above citric acid content of $1.5\times$10-4 mol. Hematite particle length and aspect ratio were decreased gradually with increasing of citric acid content. Hematite particles formed at 14$0^{\circ}C$ exhibited particle properties with the length of 0.7 ${\mu}{\textrm}{m}$ and aspect ratio of 8. Hematite particles having a good acicular-type were not obtained above 22$0^{\circ}C$.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.784-787
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• 2008

Nanoscale $YVO_4:Eu^{3+}$ phosphor has been synthesized by a mild hydrothermal reaction at various experimental conditions. The particle and luminescent properties of nanophosphors were characterized with X-ray diffraction, electron microscopy and photoluminescence. It has been found that pH value play a key factor both controlling particle size and luminous efficiency.

• Journal of the Korean Ceramic Society
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• v.38 no.11
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• pp.959-961
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• 2001

Nanosized CeO$_2$Powders were prepared under high temperature and pressure conditions by precipitation from metal nitrates with aqueous potassium hydroxide. Spherical shape of CeO$_2$powder was obtained at 175$^{\circ}C$ for 6h. TEM and X-ray diffraction patterns showed that the synthesized particle was crystalline. The average size and size distribution of the synthesized particles were below 30 nm and narrow, respectively. In addition, the effects of synthesis parameters under hydrothermal process are discussed.

• International Journal of Advanced Culture Technology
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• v.8 no.3
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• pp.231-240
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• 2020

In this paper, we present to evaluate physiological activity of Asparagopsis armata extraction. After extraction with Asparagopsis armata using hydrothermal and supercritical carbon dioxide, various physiological activities were examined. The total concentration of polyphenol compounds was determined to be 18.85 mg/g of hydrothermal Asparagopsis armata extraction and 14.74 mg/g of supercritical Asparagopsis armata extraction. In DPPH radical scavenging assay, ascorbic acid was used as positive antioxidant control. In ABTS radical scavenging assay, ascorbic acid was used as positive antioxidant control. The percentage of inhibition and IC50 were measured. The IC50 of Asparagopsis armata extraction is 261.44ppm and the IC50 of supercritical Asparagopsis armata extraction is 153.98 ppm. The elastase inhibitory assay showed concentration dependence and the IC50 of hydrothermal Asparagopsis armata extraction is 3387 ppm and the IC50 of supercritical Asparagopsis armata extraction is higher than 2500 ppm. In mushroom tyrosinase inhibition experiments, tyrosinase inhibition's IC50 of supercritical Asparagopsis armata extraction was 248.06. In the SOD-like experiments, the concentration-dependent results were showed and IC50 of hydrothermal Asparagopsis armata extraction is 845.29 ppm. In the antimicrobial experiments, maximum clear zones of supercritical Asparagopsis armata extraction represented 23.00 mm in Propionibacterium acnes. In the other hand, in experiments with the same conditions, hydrothermal Asparagopsis armata extraction had no effect in all strains.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.252.2-252.2
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• 2013

ZnO nanostructures have a lot of interest for decades due to its varied applications such as light-emitting devices, power generators, solar cells, and sensing devices etc. To get the high performance of these devices, the factors of nanostructure geometry, spacing, and alignment are important. So, Patterning of vertically- aligned ZnO nanowires are currently attractive. However, many of ZnO nanowire or nanorod fabrication methods are needs high temperature, such vapor phase transport process, metal-organic chemical vapor deposition (MOCVD), metal-organic vapor phase epitaxy, thermal evaporation, pulse laser deposition and thermal chemical vapor deposition. While hydrothermal process has great advantages-low temperature (less than $100^{\circ}C$), simple steps, short time consuming, without catalyst, and relatively ease to control than as mentioned various methods. In this work, we investigate the dependence of ZnO nanowire alignment and morphology on si substrate using of nanosphere template with various precursor concentration and components via hydrothermal process. The brief experimental scheme is as follow. First synthesized ZnO seed solution was spun coated on to cleaned Si substrate, and then annealed $350^{\circ}C$ for 1h in the furnace. Second, 200nm sized close-packed nanospheres were formed on the seed layer-coated substrate by using of gas-liquid-solid interfacial self-assembly method and drying in vaccum desicator for about a day to enhance the adhesion between seed layer and nanospheres. After that, zinc oxide nanowires were synthesized using a low temperature hydrothermal method based on alkali solution. The specimens were immersed upside down in the autoclave bath to prevent some precipitates which formed and covered on the surface. The hydrothermal conditions such as growth temperature, growth time, solution concentration, and additives are variously performed to optimize the morphologies of nanowire. To characterize the crystal structure of seed layer and nanowires, morphology, and optical properties, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Raman spectroscopy, and photoluminescence (PL) studies were investigated.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.2
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• pp.129-140
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• 1996

In this study, we have prepared corundum ($\alpha$-Al_{2}O_{3}$) single crystals from aluminum hydroxides by hydrothermal growing process and have investigated the reaction conditions. The hydrothermal conditions were mainly affected by reaction temperature, seed crystal and reaction time. Especially, seed crystal has strong effects on the particle size and crystallity of products. By adding seed crystal in Japanese gibbsite solution as the nutrient, hydrothermal reaction was performed for 2 hours at the reaction temperature of $460^{\circ}C$, to produce corundum powders which had weight mean particle diameter of $11\;\mu\textrm{m}$ with hexagonal crystal, Without adding seed crystal in Russian gibbstite solution, corundum powders that have weight mean particle diameter of $6\;\mu\textrm{m}$ with hexagonal crystals were also formed after 2 hours operation at the reaction temperature of $420^{\circ}C$.

• Economic and Environmental Geology
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• v.33 no.1
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• pp.19-30
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• 2000

The Sannae-Eonyang granitic rocks are a large fossil hydrothermal system containing the Sannae Mo-W fissure-vein type and the Eonyang amethyst deposits in the southeastern Kyongsang Basin. They evolved through similar stages showing the similarities in chemical and mineralogical compositions, fractionation trends and early magmatic fluids. Major, trace and rare earth element(REE) variations can be accounted for fractional crystallization combined with variable degrees of metasomatism. Based on the aqueous fluids exsolved directly from the crystallizing melt, the Sannae-Eonyang granitic rocks were emplaced at similar depth or pressure conditions. High temperature fluid interaction with the granitic rocks affects the elements such as K, Na, Rb, Ba, Sr, Eu, and heavy REE (HREE) mostly through feldspar re-equilibration. Although hydrothermal fluids produced partly positive Eu anomalies and HREE depletion in the granitic rocks at the Sannae Mo-W mine, the chemical concentrations defining fractionnation trends have survived the effects of alteration. Aqueous fluids exsolved from the crystallizing melt appears to be widespread, whereas fluids of moderate to low salinity and low-density with relatively high homogenization temperatures and $Co_2$-rich fluids appear to be mainly restricted and responsible for Mo-W and amethyst mineralization, respectively. Hydrothermal system of the Sannae-Eonyang granitic rocks represents repeated fluid events; from exsolution of aqueous fluids from the crystallizing melt, through fluid immiscibility and meteoric convection to later mineralization.

• Journal of the Korean Ceramic Society
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• v.42 no.7 s.278
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• pp.516-520
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• 2005

Conditions for formation of perovskite Pb(Zr$_{0.52}$Ti$_{0.48}$)O$_{3}$ phase by the hydrothermal synthesis are investigated. Pb(Zr$_{0.52}$ Ti$_{0.48}$)O$_{3}$ ceramics were synthesized by hydrothermal process above 180$^{\circ}C$ for 2 h reaction using 5$\~$30 M KOH solution as a mineralizer. Particle size increases in proportion to the mineralizer concentration. As a result of EOX analysis, PZT powders synthesized using 50 M of KOH as a mineralizer were considered as 2.42 mol$\%$ K doped-PZT powders. And 2.42 mol$\%$ K doped-PZT has much higher mechanical quality factor than undoped PZT ceramics. The sintering properties showed 7.987 g/cm$^{3}$ of sintered density and 3$\~$4 $\mu$m of grain size.

• The Korean Journal of Ceramics
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• v.5 no.4
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• pp.371-374
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• 1999

Y2O3 and Nb2O5 co-doped tetragonal zirconia polycrystals((Y, Nb)-TZP) containing 10 to 30 vol% $Al_2O_3$ were prepared and hydrothermal stability of the composites was evaluated after aging for 5 h at the temperature range of $150^{\circ}C$ $250^{\circ}C$ under 4 MPa $H_2O$ vapor pressure in an autoclave. The (Y, Nb)-TZP/Al2O3 composites showed excellent phase stability under the hydrothermal conditions, as compared with the 3Y-TZP/$Al_2O_3$ composites, due to the combined effects of the Y-Nb ordering in the $t-ZrO_2$ lattice, the reduction of oxygen vacancy concentration, and the $Al_2O_3$ addition. The strength and fracture toughness of the (Y, Nb)-TZP/$Al_2O_3$ composite, containing 20 vol% of 2.8 $Al_2O_3$ particles, were 700 MPa and 8.1 MP.$am^{1/2}$, respectively.