• Environmental Engineering Research
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• 제13권3호
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• pp.112-118
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• 2008

Residual solid in excess sludge treated by hydrothermal reaction was investigated as raw material for its recycling. Treated excess sludge and residual solid were also focused on their content change during hydrothermal reaction. Two kinds of excess sludge, obtained from a local food factory and a municipal wastewater treatment process, were tested under various conditions. Following hydrothermal reaction, depending on the reaction conditions, biodegradable substrates in treated excess sludge appeared to increase. The separated residual solid was a composite composed of organic and inorganic materials. The proportion of carbon varied from 34.0 to 41.6% depending on reaction conditions. Although 1.89% of hazardous materials were detected, SiO2 (Quartz) was a predominant constituent of the residual solid. X-ray diffraction (XRD) experiments revealed that the residual solid was of a partially amorphous state, suggesting that the residual solids could be easily converted to stable and non harmful substances through a stabilization process. Thus, this technology could be successfully used to control excess sludge and its reuse.

• 한국결정성장학회지
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• 제14권2호
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• pp.73-77
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• 2004

수열처리법을 이용하여 저품위의 잠비아산 천연 자수정의 색상 개선을 행하였다. 수열처리 조건은 다음과 같다. 즉, 수열용매 6M-HCI, 반응온도 $300^{\circ}C$, 반응시간 30시간, 충진율 40%이었다. 이와 같은 조건에서 고품질 적자색의 자수정이 얻어졌다. ICP/AES 결과로부터 색 향상은 잠비아산 자수정의 내부에 존재하는 Fe 원소의 함량이 영향을 미치는 것을 알았다. 또한 UV-VIS-NIR분석결과 처리전 잠비아산 수정과 비교해 550nm 흡수피크가 작아짐을 볼 수 있었다. 본 연구의 결과는 수열처리가 잠비아산 자수정의 상업적인 가치 증가에 있어서 적합한 방법이었다.

• 한국결정성장학회지
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• 제17권4호
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• pp.172-178
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• 2007

수평회전식 수열법에 의해 운모 분말을 합성하였다. 수열조건은 출발원료로 $K_2O,\;Al(OH)_3$ 그리고 $SiO_2$의 비는 1 : 3 : 3mol%로 하고 수열용매로 8mol%의 KOH를 함께 추가하여 $260^{\circ}C$에서 72시간 동안 반응시켰다. 합성한 분말은 수직형 수열처리법에 의한 은나노 코팅 운모 제조를 위해 사용하였다. 은나노 코팅의 처리를 위한 수열조건은 출발원료로 합성한 분말로 하고, 수열용매로 $0.5{\ell}$ 3차 증류수, 그리고 1,000ppm의 은나노 졸을 코팅원료로 사용하여 $160{\sim}260^{\circ}C$ 범위에서 72시간 동안 반응시켰다. 처리 후 결정구조, 은나노 코팅 여부 및 코팅된 운모의 특성은 XRD, SEM, TEH-EDX 및 shake plask법을 통해 분석하였다.

• 한국결정성장학회지
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• 제11권5호
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• pp.185-189
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• 2001

비정질 인산알루미늄 분말은 화학양론조성비의 $Al_2(SO_4)_3$와 $H_3PO_4$혼합물을 NaOH 또는 KOH 용액을 이용하여 중화 반응시킨 뒤 이를 수열침전법에 의해 단일상으로 얻을 수 있었으며, 합성조건은 다음과 같다. 즉, 출발원료; $Al_2(SO_4)_3$와 $H_3PO_4$, 중화반응의 pH범위; 5.6~6.0, 수열반응의 온도범위; 170~$180^{\circ}C$, 수열반응의 시간범위; 4~5시간이었다. 이와 같은 조건하에서 얻어진 생성물은 0.1~0.3$\mu\textrm{m}$ 크기의 비정질 인산알루미늄 미립자였으며 그리고 미국약전에 따라 실험한 결과 모두 적합하였다.

• 한국분말재료학회지
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• 제28권2호
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• pp.127-133
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• 2021

One-dimensional (1D) piezoelectric nanostructures are attractive candidates for energy generation because of their excellent piezoelectric properties attributed to their high aspect ratios and large surface areas. Vertically grown BaTiO₃ nanotube (NT) arrays on conducting substrates are intensively studied because they can be easily synthesized with excellent uniformity and anisotropic orientation. In this study, we demonstrate the synthesis of 1D BaTiO₃ NT arrays on a conductive Ti substrate by electrochemical anodization and sequential hydrothermal reactions. Subsequently, we explore the effect of hydrothermal reaction conditions on the piezoelectric energy conversion efficiency of the BaTiO₃ NT arrays. Vertically aligned TiO₂ NT arrays, which act as the initial template, are converted into BaTiO₃ NT arrays using hydrothermal reaction with various concentrations of the Ba source and reaction times. To validate the electrical output performance of the BaTiO₃ NT arrays, we measure the electricity generated from each NT array packaged with a conductive metal foil and epoxy under mechanical pushings. The generated output voltage signals from the BaTiO₃ NT arrays increase with increasing concentration of the Ba source and reaction time. These results provide a new strategy for fabricating advanced 1D piezoelectric nanostructures by demonstrating the correlation between hydrothermal reaction conditions and piezoelectric output performance.

• 신재생에너지
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• 제16권4호
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• pp.83-91
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• 2020

In this study, the reusability of the Fenton oxidation solution was evaluated to reduce the cost of the pretreatment process. Biomass was sequential subjected to Fenton oxidation-hydrothermal treatment and enzymatic hydrolysis to produce monosaccharides. The liquid solution recovered after Fenton oxidation contained OH radicals with a concentration of 0.11 mol/L. This liquid solution was reused for a new Fenton oxidation reaction. After Fenton oxidation, hydrothermal treatment was performed under the same conditions as before, and 9.34-13.63 g/L of xylose was detected. This concentration was slightly lower than that of a fresh Fenton oxidation solution (16.51 g/L) but was higher than that obtained by hydrothermal treatment without Fenton oxidation (2.72 g/L). The degradation rate during hydrothermal pretreatment involving Fenton oxidation was 36.02%, which decreased (29.24-31.05%) slightly when the liquid solution recovered after Fenton oxidation was reused. However, the degradation rate increased compared to that measured from hydrothermal treatment without Fenton oxidation (15.21%). Moreover, the yield after enzyme hydrolysis decreased in the following order: fresh Fenton oxidation-hydrothermal treatment (89.64%) > Fenton oxidation with reused solution-hydrothermal treatment (74.84%) > hydrothermal treatment without Fenton oxidation (32.05%).

• International Journal of Concrete Structures and Materials
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• 제10권1호
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• pp.15-28
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• 2016

With the aim to reduce the atmospheric $CO_2$, utilization of the carbonated lime produced from the aqueous carbonation reaction for the synthesis of a cementitious material would be a promising approach. The present investigation deals with the aqueous carbonation of slaked lime, followed by hydrothermal synthesis of a cementitious material utilizing the carbonated lime, silica fume, and hydrated alumina. In this study, the aqueous carbonation reaction was performed under four different conditions. The TGA, FESEM, and XRD analysis of the carbonated product obtained from the four different reaction conditions was performed to evaluate the efficacy of the reaction conditions used for the production of the carbonated lime. Additionally, the performance of the cementitious material was verified analyzing the physical characteristics, mechanical property and setting time. Based on the results, it is demonstrated that the material produced by the hydrothermal method possesses the cementing ability. Additionally, it is revealed that the mortar prepared using the alternative cementitious material yields $33.8{\pm}1.3MPa$ compressive strength. Finally, a plausible reaction scheme has been proposed to explain the overall performances of the aqueous carbonation as well as the hydrothermal synthesis of the cementitious material.

• 한국지하수토양환경학회지:지하수토양환경
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• 제29권1호
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• pp.63-71
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• 2024

Hydrothermal Reaction (HTR) was applied for the stabilization of contaminated soil with heavy metals, and then the test determined the optimal conditions for HTR. After HTR, the concentration of heavy metals in the contaminated soil increased. However, it was observed that the leachability potential significantly decreased as determined by TCLP and SPLP tests. This decrease was attributed to a decline in fractions 1-2 and an increase in fractions 3-4 as revealed by sequential extraction procedure. Due to the mineralogical characteristics of the dredged soil, distinct changes were not evident in the five-stage fraction. Therefore, it is deemed necessary to understand the chemical and mineralogical characteristics of the target soil for HTR application in order to selectively address contaminants. Comparison among operating conditions determined the optimal condition to be at 240℃ for one hour.

• 한국분말재료학회지
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• 제26권6호
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• pp.481-486
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• 2019

Iron oxides currently attract considerable attention due to their potential applications in the fields of lithiumion batteries, bio-medical sensors, and hyperthermia therapy materials. Magnetite (Fe₃O₄) is a particularly interesting research target due to its low cost, good biocompatibility, outstanding stability in physiological conditions. Hydrothermal synthesis is one of several liquid-phase synthesis methods with water or an aqueous solution under high pressure and high temperature. This paper reports the growth of magnetic Fe₃O₄ particles from iron powder (spherical, <10 ㎛) through an alkaline hydrothermal process under the following conditions: (1) Different KOH molar concentrations and (2) different synthesis time for each KOH molar concentrations. The optimal condition for the synthesis of Fe₃O₄ using Fe powders is hydrothermal oxidation with 6.25 M KOH for 48 h, resulting in 89.2 emu/g of saturation magnetization at room temperature. The structure and morphologies of the synthesized particles are characterized by X-ray diffraction (XRD, 2θ = 20°-80°) with Cu-kα radiation and field emission scanning electron microscopy (FE-SEM), respectively. The magnetic properties of magnetite samples are investigated using a vibrating sample magnetometer (VSM). The role of KOH in the formation of magnetite octahedron is observed.

• 한국결정성장학회지
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• 제15권4호
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• pp.145-151
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• 2005

어두운 적색을 나타내는 아프리카산 천연루비의 색상개선을 열처리법과 수열처리법을 이용하여 행한 결과, 열처리법은 색상이 떨어지는 역효과가 발생하였다. 그러나 수열처리법의 경우에는 색상과 투명도가 향상되었다. 아프리카산 천연루비의 색상개선에 대한 수열처리 조건은 다음과 같다. 즉, 수열용매 1M $Na_2CO_3-0.9M\;K_2CO_3$, 반응온도: $450^{\circ}C$, 반응 시간: 48hrs, 충전율: $30\%$, 압력: 375atm이었다. 이와 같은 조건에서 얻어진 루비의 특성을 평가한 결과, ICP/MS와 XRF 분석결과로부터 수열처리 후 $Cr^{3+},\;Fe^{3+},\;Ti^{4+}$ 등의 함량이 수열처리 전의 루비에 비해 감소됨을 알 수 있었으며, 이로 인하여 적색이 밝아지는 것을 색차계 분석결과로부터 알았다. 이 결과는 수열처리 전과 비교하였을 때 $Cr^{3+}$ 이온의 전자전이에 의해 발생되는 발광피크의 강도가 수열처리 후 감소한 PL분석결과와 잘 일치하였다.