• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.9
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• pp.561-564
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• 2015

Nano-size $BaTiO_3$ powder was synthesized by relatively simple hydrothermal reaction method. Finely dispersed Ti hydroxide precursor was first precipitated using $Ti(SO_4)_2$ and NaOH solution by applying ultrasonic power and washed thoroughly to remove $SO_4{^{2-}}$ and $Na^+$ ion. Then hydrothermal reaction was done at $160^{\circ}C$ for 6 hrs using solution prepared by washed Ti hydroxide precursor slurry and $Ba(OH)_2{\cdot}8H_2O$ with Ti:Ba mole ratio of 1:1. 200 ~ 500 nm size and uniform size distributed $BaTiO_3$ powder was synthesized by relatively low temperature and simple process.

• Proceedings of the Korean Ceranic Society Conference
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• 2003.04a
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• pp.153.1-153
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• 2003

• Korean Journal of Materials Research
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• v.21 no.8
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• pp.415-418
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• 2011

Tin (IV) dioxide ($SnO_2$) has attracted much attention due to its potential scientific significance and technological applications. $SnO_2$ nanoparticles were prepared under low temperature and pressure conditions via precipitation from a 0.1 M $SnCl_4{\cdot}5H_2O$ solution by slowly adding $NH_4OH$ while rapidly stirring the solution. $SnO_2$ nanoparticles were obtained from the reaction in the temperature range from 130 to $250^{\circ}C$ during 6 h. The microstructure and phase of the synthesized tin oxide particles were studied using XRD and TEM analyses. The average crystalline sizes of the synthesized $SnO_2$ particles were from 5 to 20 nm and they had a narrow distribution. The average crystalline size of the synthesized particles increased as the reaction temperature increased. The crystalline size of the synthesized tin oxide particles decreased with increases in the pH value. The X-ray analysis showed that the synthesized particles were crystalline, and the SAED patterns also indicate that the synthesized $SnO_2$ nanoparticles were crystalline. Furthermore, the morphology of the synthesized $SnO_2$ nanoparticles was as a function of the reaction temperature. The effects of the synthesis parameters, such as the pH condition and reaction temperature, are also discussed.

• Journal of Sensor Science and Technology
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• v.28 no.4
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• pp.256-261
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• 2019

In this study, mid-infrared transparent zinc sulfide (ZnS) ceramics were fabricated through hydrothermal synthesis with different molar ratios of S/Zn (S/Zn = 0.8, 1.0, 1.2, 1.4, and 1.6). The ZnS ceramics were sintered at a relatively low temperature of $850^{\circ}C$ to prevent the occurrence of the hexagonal phase featuring optical anisotropy. The phase composition, microstructure, and optical properties of the ZnS ceramics were subsequently investigated by employing X-ray diffraction, scanning electron microscopy, and Fouriertransform infrared spectroscopy. The results obtained indicate that the ZnS nanoparticles feature the cubic phase, without the hexagonal phase. Moreover, with increasing S, the crystallinity and particle size of the ZnS nanoparticles increased. The crystallinity and density of the ZnS ceramics improved when the molar ratio of S was higher than the molar ratio of Zn, thereby enhancing the transmittance. Furthermore, the ZnS ceramic with an S/Zn value of 1.2 was found to exhibit the highest transmittance of approximately 69% owing to the reduced occurrence of the hexagonal phase and a high density of 99.8%.

• Journal of the Mineralogical Society of Korea
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• v.13 no.4
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• pp.171-185
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• 2000

Siliceous mudstones are embedded on a large scale in the Tertiary formations of Pohang area. Some useful zeolites such as NsP, (Na, TMA)P, analcime and hydroxysodalite were synthesized from the siliceous mudstones by treating with the variety of solution, i.e ., NaOH, NaOH+NaCl, NaOH, NaOH+$NaAlO_2$and NaOH+TMAOH at the low-temperature hydrothermal system ranging 60~12$0^{\circ}C$. Major precursor of zeolites is found as opal-CT in the zeolite-forming reaction. Smectite, which is included in considerable amounts in the mudstone, appears to play a major role of Al-source in the zeolite synthesis. In comparison, chalcedonic quartz and mica are rather insoluble in alkaline solution, and thus, these are observed as major impurities in the reaction products. An addition of $NaAlO_2$to NaOH solution is effective for eliminating these impurities in the reaction procedure, through these are partly dissolved when elevating the reaction temperature, concentration, and time. Phase change from NaP to hydroxysodalite takes place at the NaOH concentrations of 3.0~4.0 M, and the reaction is not sensitive to the temperature shift. NaP is more stable at lower NaOH concentration and higher activity of $Na_{+}$ whereas analcime is sensitive to the temperature change and stable at higher than $100^{\circ}C$ and 2.0~4.0 M in NaOH concentration. For the pure NaP synthesis without any other products, the treatment of mudstones with 1:1 solution of NaOH and $NaAlO _2$ turns out to be quite effective. NaP was successfully synthesized together with analcime at $100^{\circ}C$ as well as lower concentrations of NaOH+NaCl solution. In addition, the organic type, (Na, TMA)P was formed together with smectite in the 1:1 solution of NaOH and TMAOH.

• Korean Journal of Materials Research
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• v.34 no.8
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• pp.387-394
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• 2024

Transition metal oxide-based materials have mainly been studied as electrodes for energy storage devices designed to meet essential energy demands. Among transition metal oxide-based materials, hydrated vanadium pentoxide (V₂O₅·nH₂O), a vanadium oxide material, has demonstrated great electrochemical performance in the electrodes of energy storage devices. Graphene oxide (GO), a carbon-based material with high surface area and high electrical conductivity, has been added to V₂O₅·nH₂O to compensate for its low electrical conductivity and structural instability. Here, V₂O₅·nH₂O/GO nanobelts are manufactured with water without adding acid to ensure that the GO is uniformly dispersed, using a microwave-assisted hydrothermal synthesis. The resulting V₂O₅·nH₂O/GO nanobelts exhibited a high specific capacitance of 206 F/g and more stable cycling performance than V₂O₅·nH₂O without GO. The drying conditions of the carbon paper electrodes also resulted in more stable cycling performance when conducted at high vacuum and high temperature, compared with low vacuum and room temperature conditions. The improvement in electrochemical performance due to the addition of GO and the drying conditions of carbon paper electrodes indicate their great potential value as electrodes in energy storage devices.

• Korean Chemical Engineering Research
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• v.57 no.1
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• pp.133-141
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• 2019

High specific surface area zirconia with acid-basic property was synthesized by precipitation using reflux method or hydrothermal synthesis method using ammonium hydroxide solution as precipitant in the range of pH of Zr solution from 2 to 10. The prepared zirconia was characterized by the nitrogen adsorption, X-ray diffraction (XRD), isopropanol temperature programmed desorption (IPA-TPD), scanning electron microscopy and X-ray photoelectron spectroscopy, and the catalytic activity in the IPA decomposition reaction was correlated with the acid-basic properties. When using reflux method, high pH of Zr solution was required to obtain high fraction of tetragonal zirconia, and pure tetragonal zirconia was possible at pH 9 or higher. High pH was required to obtain high specific surface area zirconia, and the hydrous zirconia synthesized at pH 10 had high specific surface area zirconia of $260m^2g^{-1}$ even after calcination at $600^{\circ}C$. However, hydrothermal synthesis with high pressure under the same conditions resulted in very low specific surface area below $40m^2g^{-1}$ and monoclinic phase zirconia was synthesized. High pH of the solution was required to obtain high specific surface area tetragonal phase zirconia. In hydrothermal synthesis requiring high pressure, monoclinic zirconia was produced irrespective of the pH of the solution, and the specific surface area was relatively low. Zirconia with high specific surface area and tetragonal phase was predominantly acidic compared to basicity and only propylene, which was observed as selective dehydration reaction in IPA decomposition reaction, was produced.

• Corrosion Science and Technology
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• v.23 no.1
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• pp.72-81
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• 2024

The Ti-6Al-4V alloy is widely used as an implant material due to its higher fatigue strength and strengthto-weight ratio compared to pure titanium, excellent corrosion resistance, and bone-like properties that promote osseointegration. For rapid osseointegration, the adhesion between the titanium surface and cellular biomolecules is crucial because adhesion, morphology, function, and proliferation are influenced by surface characteristics. Polymeric peptides and similar coating technologies have limited effectiveness, prompting a demand for alternative materials. There is growing interest in 2D nanomaterials, such as MoS₂, for good corrosion resistance and antibacterial, and bioactive properties. However, to coat MoS₂ thin films onto titanium, typically a low-temperature hydrothermal synthesis method is required, resulting in the synthesis of films with a toxic 1T@2H crystalline structure. In this study, through high-temperature annealing, we transformed them into a non-toxic 2H structure. The implant coating technique proposed in this study has good corrosion resistance and biocompatibility, and antibacterial properties.

• Bulletin of the Korean Chemical Society
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• v.34 no.11
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• pp.3335-3339
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• 2013

Boron-doped ZnO (BZO) nanorods were grown on quartz substrates using hydrothermal synthesis, and the temperature-dependence of their photoluminescence (PL) was measured in order to investigate the origins of their PL properties. In the UV range, near-band-edge emission (NBE) was observed from 3.1 to 3.4 eV; this was attributed to various transitions including recombination of free excitons and their longitudinal optical (LO) phonon replicas, and donor-acceptor pair (DAP) recombination, depending on the local lattice configuration and the presence of defects. At a temperature of 12 K, the NBE produces seven peaks at 3.386, 3.368, 3.337, 3.296, 3.258, 3.184, and 3.106 eV. These peaks are, respectively, assigned to free excitons (FX), neutral-donor bound excitons ($D^{\circ}X$), and the first LO phonon replicas of $D^{\circ}X$, DAP, DAP-1LO, DAP-2LO, and DAP-3LO. The peak position of the FX and DAP were also fitted to Varshni's empirical formula for the variation in the band gap energy with temperature. The activation energy of FX was about ~70 meV, while that of DAP was about ~38 meV. We also discuss the low temperature PL near 2.251 eV, related to structural defects.

• Proceedings of the KAIS Fall Conference
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• 2011.12a
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• pp.357-360
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• 2011

A new copper adenine MOF (Bio-MOF) was synthesized by hydrothermal procedure and explored for its low temperature $CO_2$ adsorption. In this adenine a DNA nucleotide was used as a ligand for Cu in DMF solution at $130^{\circ}C$. The synthesized Bio MOF was characterized by XRD, SEM, EDS, TG and BE Tresults. The material possesses high surface area (716.08 $m^2g^{-1}$) with mono dispersed particles of about 2.126 nm. The maximum $CO_2$ adsorption capacity is 5wt% at $50^{\circ}C$, which is regenerable at $100^{\circ}C$ which is very low when compared to other metal organic frame work studied. This study proves that the synthesized material is also be a choice materials for low temperature $CO_2$adsorption.