• Journal of the Korean Ceramic Society
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• v.29 no.12
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• pp.997-1003
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• 1992

Ultra-fine hydroxyapatite powders were synthesized by the hydrothermal reaction of Ca(OH)2 suspension or Ca(NO3)2$.$4H2O solution with (NH4)2HPO4 solution, and the powders were characterized for each synthetic condition. Crystalline hydroxyapatite powders have average grain size of less than 50 nm. By increasing the reaction pressure, the crystallinity was improved, and the crystals were preferentially growing along c-axis. When Ca(NO3)2$.$4H2O of high solubility was used, hydroxyapatite of single phase was produced. However when Ca(OH)2 of low solubility was used more than 0.334 mol/ι, unreacted Ca(OH)2 remained. Diffraction spot patterns of transmission electron microscope show that powders synthesized by the hydrothermal reaction were composed of single crystals of hexagonal phase.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.6
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• pp.481-485
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• 2012

ZnO nanowires were synthesized by hydrothermal technique. Prepared synthesis aqueous solutions were preserved by preheating in autoclave type synthesis equipment with various preheating time of 1 h difference. ITO-coated corning glass substrates deposited with AZO seed layers were then inserted in the preheated synthesis aqueous solutions and ZnO nanowires were grown for 180 min at $90^{\circ}C$. Density, length and aspect ratio of the grown ZnO nanowires were investigated. Composition, structural and optical properties of the grown ZnO nanowires were analyzed. Characteristics of the ZnO nanowires were comparatively studied in relation with $Zn^{2+}$ ion concentration measured directly after the preheating of synthesis aqueous solution.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2014.11a
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• pp.260-261
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• 2014

$TiO_2$ nanotubes (TNT) synthesized by microwave-assisted hydrothermal method by using $TiO_2-P25$ as a precursor at hydrothermal temperature $150^{\circ}C$ in 4 hours. The concentration of alkaline solution is between 4M and 10M. Samples were characterized by X-ray diffraction (XRD), Raman spectroscopy (RS), Transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) and UV-vis DRS spectroscopy. The results demonstrated the effects of the alkali concentration to the formation of nanotubes. The photocatalytic activity was investigated by degradation of Methylene Blue (MB).

• Proceedings of the KIEE Conference
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• 1987.11a
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• pp.97-100
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• 1987

An improved hydrothermal unit commitment algorithm is proposed for the purpose of optimal operation of electric power system. Especially, Dynamic Programming Method which is main scheme of the algorithm is modified to assure the feasible solution all the time. The effectiveness of the algorithm has been demonstrated by applying to a sample system.

• 한국신재생에너지학회:학술대회논문집
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• 2005.11a
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• pp.656-659
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• 2005

Nanocrystalline ceria powders were prepared by hydrothermal treatment of cerium(IV) ammonium nitrate solution without a precipitating agent. A systematic investigation of the effect of hydrothermal temperature and react ion time on the physical properties of the product powders was carried out. When the hydrothermal temperature was increased, the product ceria powders exhibited larger crystallite size with higher yield. Increasing reaction time produced more crystalline ceria powders attributed to further hydrothermal reactions and structural rearrangement. The physical properties of ceria powders can be control led by adjusting the hydrothermal conditions.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.16 no.6
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• pp.240-243
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• 2006

The significant color enhancement in low quality Australian natural sapphire has been achieved by a hydrothermal method. The optimal conditions for the color enhancement of Australian natural sapphire were as follows; hydrothermal reaction temperature: $320{\sim}350^{\circ}C$, duration : 3 days, hydrothermal solvent: 2 M NaOH solution. After the hydrothermal treatment, Australian natural sapphires of transparent colors were obtained, and their grades were found to be improved from commercial to middle/top grade by value chart analysis.

• Journal of Electrical Engineering and Technology
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• v.9 no.6
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• pp.1882-1890
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• 2014

This paper proposes an augmented Lagrange Hopfield network (ALHN) based method for solving multi-objective short term fixed head hydrothermal scheduling problem. The main objective of the problem is to minimize both total power generation cost and emissions of $NO_x$, $SO_2$, and $CO_2$ over a scheduling period of one day while satisfying power balance, hydraulic, and generator operating limits constraints. The ALHN method is a combination of augmented Lagrange relaxation and continuous Hopfield neural network where the augmented Lagrange function is directly used as the energy function of the network. For implementation of the ALHN based method for solving the problem, ALHN is implemented for obtaining non-dominated solutions and fuzzy set theory is applied for obtaining the best compromise solution. The proposed method has been tested on different systems with different analyses and the obtained results have been compared to those from other methods available in the literature. The result comparisons have indicated that the proposed method is very efficient for solving the problem with good optimal solution and fast computational time. Therefore, the proposed ALHN can be a very favorable method for solving the multi-objective short term fixed head hydrothermal scheduling problems.

• 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.

• Korean Journal of Materials Research
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• v.15 no.2
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• pp.134-138
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• 2005

This study was performed to investigate the surface properties of electrochemically oxidized pure niobium by anodic oxide and hydrothermal treatment technique. Niobium specimens of $10mm\times10mm\times1.0mm$ in dimension were polished sequentially from $\#600,\;\#800,\;\#1000$ emery paper. The surface of pure niobium sperimens was anodized in an electrolytic solution that was dissolved calcium and phosphate in water. The electrolytic voltage was set in the range of 250 V and the current density was $10mA/cm^2$. The specimen was hydrothermal treated in high-pressure steam at $300^{\circ}C$ for 2 hours using an autoclave. And all specimens were immersed in the in the Hanks' solution nth pH 7.4 at $37^{\circ}C$ for 30 days. The surface of specimen was characterized by surface roughness, scanning electron microscope(SEM), energy dispersion X-ray analysis(EDX), X-ray photoemission spectroscopy(XPS) test. The value of surface roughness was the highest in the anodized sample and $0.41{\pm}0.04\;{\mu}m$. The results of the SEM observation show that oxide layers of the multi porosity in the anodized sample were piled up on another, and hydroxyapatite crystal was precipitate from the surface of the hydrothermal treated sample. In the XPS analysis, O, Nb, C peak and small amounts of N peak were found in the polished specimens while Ca and P peak in addition to O, Nb, C and peak were observed in the hydrothermal treated sample.

• Clean Technology
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• v.28 no.2
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• pp.154-162
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• 2022

Microstructured Al@Al₂O₃ and Al@Ni-Al LDH (LDH = layered double hydroxide) core-shell metal-ceramic composites are prepared by hydrothermal reactions of aluminum (Al) metal substrates. Controlled hydrothermal reactions of Al metal substrates induce the hydrothermal dissolution of Al ions at the Al-substrate/solution interface and reconstruction as porous metal-hydroxides on the Al substrate, thereby constructing unique metal-ceramic core-shell composite structures. The morphology, composition, and crystal structure of the core-shell composites are affected largely by the ions in the hydrothermal solution; therefore, the critical physicochemical and surface properties of these unique metal-ceramic core-shell microstructures can be modulated effectively by varying the solution composition. A Ni/Al@Al₂O₃ catalyst with highly dispersed catalytic Ni nanoparticles on an Al@Al₂O₃ core-shell substrate was prepared by a controlled reduction of an Al@Ni-Al LDH core-shell prepared by hydrothermal reactions of Al in nickel nitrate solution. The reduction of Al@Ni-Al LDH leads to the exolution of Ni ions from the LDH shell, thereby constructing the Ni nanoparticles dispersed on the Al@Al₂O₃. The catalytic properties of the Ni/Al@Al₂O₃ catalyst were investigated for CO₂ methanation reactions. The Ni/Al@Al₂O₃ catalyst exhibited 2 times greater CO₂ conversion than a Ni/Al₂O₃ catalyst prepared by conventional incipient wetness impregnation and showed high structural stability. These results demonstrate the high effectiveness of the design and synthesis methods for the metal-ceramic composite catalysts derived by hydrothermal reactions of Al metal substrates.