• Clean Technology
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• v.25 no.1
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• pp.74-80
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• 2019

Thermochemical treatment of sewage sludge is an energy-intensive process due to its high moisture content. To save the energy consumed during the process, the hydrothermal carbonization process for sewage sludge can be used to convert sewage sludge into clean solid fuel without pre-drying. This study is aimed to investigate co-firing characteristics of the hydrothermally carbonated sewage sludge (HCS) to a pulverized coal combustion system. The purpose of the measurement is to measure the pollutants produced during co-firing and combustion efficiency. The combustion system used in this study is a furnace with a down-firing swirl burner of a $80kW_{th}$ thermal input. Two sub-bituminous coals were used as a main fuel, and co-firing ratio of the sewage sludge was varied from 0% to 10% in a thermal basis. Experimental results show that $NO_x$ is 400 ~ 600 ppm, $SO_x$ is 600 ~ 700 ppm, and CO is less than 100 ppm. Experimental results show that stable combustion was achieved for high co-firing ratio of the HCS. Emission of $NO_x$ and $SO_x$ was decreased for higher co-firing ratio in spite of the higher nitrogen contents in the HCS. In addition, it was found that the pollutant emission is affected significantly by composition of the main fuel, regardless of the co-firing ratios.

• Solar Energy
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• v.12 no.1
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• pp.95-102
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• 1992

A small scale solar collector system composed of a Fresnel lens of $0.5m^2$ area as a solar concentrator and a compact fluidized-bed solar receiver was developed. Performance and temperature distribution in the fluidized bed receiver were measured using SiC for particles and air for working fluid. The maximum gas temperature was attained up to 1250K at this moment. In this study, energy efficiency achieved by the present experiment was high for the small scale solar collector system and compact receiver.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.6
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• pp.298-304
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• 2009

The effect of the surface treatments on the high temperature properties of the Inconel 617, one of the promising candidate alloys for high temperature heat-transport system, has been studied. Various surface modification methods including a rapid thermal process(RTP), a hydrothermal treatment, and a physical vapor deposition($2{\mu}m$ thick TiAlN film by an arc discharge) were applied to the Inconel 617. The morphological and the structural properties of the surface-modified Inconel 617 samples after heat treatment at $1000^{\circ}C$ in the air were compared to find out whether inhomogeneous formation of $Cr_2O_3$ crust at the surface region was suppressed or not. TiAlN-coated Inconel 617 showed homogeneous microstructure and the lowest wear loss compared to bare, RTP- and hydrothermally-treated Inconel 617 by suppressing the $Cr_2O_3$ crust formation.

• Journal of the Korea Organic Resources Recycling Association
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• v.31 no.1
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• pp.27-34
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• 2023

In this study, spent mushroom substrate (SMS), which consits of lignocellulosic material, was pretreated by hydrothermal method; the changes of biodegradability and methane production yield of pretreated SMS were determined according to formation of lignocellulosic biomass degrading byproducts formation during thermal pretreatment. Based on the results, all hydrothermal pretreatment temperatures showed improved solubilization performance for biomass, and the optimum pretreatment effect was observed at an pretreatment temperature of 150℃ with the highest methane production yield. However, the induced formation of furan derivatives (i.e., 5-hydroxymethylfurfural and furfural) as byproducts during hydrolysis of hemicellulose and cellulose at severe condition lowered biodegradability and methane yield when the hydrothermal pretreatment temperature was higher than 180℃. Thus, this study revealed that hydrothermal pretreatment could promote anaerobic digestion efficiency of lignocellulosic biomass and is of great importance for preventing byproducts formation through pretreatment condition control.

• Korean Chemical Engineering Research
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• v.45 no.5
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• pp.448-454
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• 2007

Hydrothermal synthesis was conducted with starting material as Barium hydroxide and hydrous titania ($TiO_2{\cdot}xH_2O$) to obtain barium titanate fine Powder. The conversion, crystal structure and properties of as-prepared powder were investigated according to reaction temperature, time and concentration. The effect of variables on conversion was in order of time < temperature < concentration and the maximum conversion reached to 99.5% in the case of hydrothermal synthesis at $180^{\circ}C$ for 2 h with 2.0 M reactant concentration. At low concentration such as 0.25 M, formation of unreacted $BaCO_3$ and $TiO_2$ was not inevitable at even high reaction temperature and these components converted into $BaTi_2O_5$ at high temperature and remained as impurity. As concentration of reactant increased, the size of as-synthesized $BaTiO_3$ powder deceased and Ba/Ti molar ratio approached into 1, showing Ba/Ti ratio of $1{\pm}0.005$ for reaction at $180^{\circ}C$ for 2 h with 2.0 M concentration.

• Journal of the Korea Organic Resources Recycling Association
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• v.25 no.1
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• pp.47-55
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• 2017

The technology for hydrothermal reaction of organic waste is one of the promising process to improve energy efficiency of biomass waste recycling system since moisture contents of treated biomass could be reduced at 40% or less than by dehydration processes. For these reasons, many parts of the world are interested in hydrothermal reaction of organic waste. In this paper, drying performances were evaluated with and without hydrothermal reaction of organic wastes which are sewage sludge and food wastes. For the hydrothermal reaction, organic wastes were treated at $200^{\circ}C$ for 1hr. Drying time of treated organic waste by hydrothermal reaction was reduced. In case of food waste drying at $100^{\circ}C$, drying time of treated wasted was reduced more 52.9% than non-treated. Hence, drying performances of sewage sludge and food wastes should be improved by hydrothermal reaction. Drying rates of treated wastes were considerably increased at preheat period of drying characteristic curve as followings; at $80^{\circ}C$ sludge as 148%, $100^{\circ}C$ sewage sludge as 151%, $80^{\circ}C$ food waste as 209%, $100^{\circ}C$ food waste as 366%. It means the surface area of treated wastes could be increased with destruction of cell membrane by hydrothermal reaction. However, the designer and operator of drying process should be careful, since enhanced drying rate cause the extension the decreasing drying period.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.30 no.3
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• pp.91-95
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• 2020

In this study, we report a hydrothermal synthesis in which BaTiO₃ nanoparticles (NPs) with enhanced size uniformity and dispersibility are synthesized by increased time and temperature, increasing nucleation and diffusion rates. The formation process of an uniform size of 20 nm BaTiO₃ NPs, which has not been extensively researched, was optimized through hydrothermal synthesis at 180℃. Simultaneous increase in the nucleation rate of TiO₂ and diffusion length of Ba²⁺ ions, resulting from a higher temperature, allowed for the synthesis of BaTiO₃ NPs (20 nm) with significantly enhanced size-uniformity. The size and crystallinity of BaTiO₃ NPs which exhibit excellent dispersibility in hexane solvent were investigated using transmission electron microscopy and X-ray diffraction. The results presented herein provide insights into improving the size uniformity and dispersibility of BaTiO₃ NPs by hydrothermal synthesis for applications to variety of electronic devices.

• Korean Journal of Crystallography
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• v.7 no.1
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• pp.30-35
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• 1996

Calcite(CaCO3) single crystals were grown hydrothermally and transmittance of as grown crystals was measured. Instead of platinium, teflon was lined onto the wall of autoclave to prevent the corrosion of autoclave wall by acidic NH4Cl solution. Spontaneous nucleation and growth of calcite crystal on teflon was reduced considerably by addition of NaCl and /or CH3COOH and applying low temperature gradient. When the temperature gradient exceeded to a few degrees from the critical temperature gradient(6-7℃), spontaneous nucleation and growth was rapidly increased in any hydrothermal solutions. Precise temperature control is thought to be the most important factor for the growth of calcite single crystal by hydrothermal technique. As grown calcite single crytal showed high transmittance compared to natural one by UV-visible analysis.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.57.1-57.1
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• 2009

나노이산화티타늄은 인체에는 화장품, 의약, 식품분야 등에 쓰이고 외부 환경 재료에는 광촉매로서 유독가스 정화제, 옥내 외 항균, 수소발생 가시광 응답형 촉매 및 멤브레인 필터 등과 전자소재용 유전재료, 발광 재료 등 용도가 다양하다. 나노 산화티타늄 화합물의 제조법은 수열합성법, 기상법 등 여러 방법이 있다. 이들에 대한 리뷰의 목적은 2009년도 정부의 투자 계획 중에서 본제목에 관련되는 핵심 산업 재원 원천기술 개발, 태양광, 풍력 등의 신재생 에너지 개발, 록색 기술 개발을 통한 에너지절약형 LED 개발, 차세대 핵심환경 기술 개발, 핵심나노기반기술개발 등의 개발을 위하여 4,363억 원의 예산을 편성하고 연구자와 기술자들이 참여하여 유익한 실적이 창출되기를 원하고 있으므로 본 발표자들은 이 분야에서 연구하는 연구자와 기술자들에게 이 분야에 관련되는 자료를 참고로 제시하는데 있다. 페로브스카이트형 산화물인 유전재료($BaTiO_3$), 발광재료(CaTiO3:Pr3+적색), 박막형 반응기재료($Ca0.8Sr0.2TiO_3$), 등의 여러 가지 산화물은 류통식 급속 승온 수열 합성법, 겔 졸 법, 수열 합성법 등 여러 방법에 의하여 페로브스카이트형 산화물 입자 직경이 약 20nm~100nm 범위까지 합성된다. 태양광을 조사하여 물을분해 해서 수소를 생산하는 산화티타늄계 가시광 응답형 Vis-$TiO_2$ 박막은 기상법으로 제조하는데 한 예로써 RF 스퍼터링법으로 박막을 제조하여 수소와 산소를 회수하였으며, 황도프산화티타늄, 질소 도프 산화티타늄은 유기물 분해에 의한 공해제거, $NO_x$ 제거 등 환경정화에 사용되고, 고온 고압수법/산화티타늄 복합기술에 의해서는 바이오매스 분해 하고, 일종의 수열법인 개량형 HyCOM 법은 가시광 응답성 산화티타늄을 합성하여 NO가스 제거에 사용한다. 이들 여러 방법에 관한 것을 소개하고저 한다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.4 no.3
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• pp.223-229
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• 1994

$KTP(KTiOPO_4)$ single crystals have been hydrothermally grown in KOH solutions. Properties and Raman spectra of grown crystal were investigated. The most effective solvents for the crystal growth of KTP were KOH and KF solutions. In this study, the properties of KTP single crystals grown hydrothermally at $500^{\circ}C$ in 9 m KOH solution were measured. The following results were obtained : lattice parameters ; a=1.281 nm and c=1.058 nm, density ; $2.94 g/cm^3$, Vickers hardness ; $562kg/cm^2$, refractive indices ; $n_e=1.740$ and $n_e= 1.747.$ And Raman spectra of hydrothermal growth KTP single crystal have been investigated at room temperature under atmospheric pressure. As a result, the $A_1$ modes agree very well with KTP single crystal of high temperatures solution growth but the behavior of $B_2$ modes were slightly different.