• Journal of Korean Society of Water and Wastewater
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• v.29 no.1
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• pp.57-63
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• 2015

Recently, Korea's municipal wastewater treatment plants generated amount of wastewater sludge per day. However, ocean dumping of sewage sludge has been prohibited since 2012 by the London dumping convention and protocol and thus removal or treatment of wastewater sludge from field sites is an important issue on the ground site. The hydrothermal carbonization is one of attractive thermo-chemical method to upgrade sewage sludge to produce solid fuel with benefit method from the use of no chemical catalytic. Hydrothermal carbonization improved that the upgrading fuel properties and increased materials and energy recovery, which is conducted at temperatures ranging from 200 to $350^{\circ}C$ with a reaction time of 30 min. Hydrothermal carbonization increased the heating value though the increase of the carbon and fixed carbon content of solid fuel due to dehydration and decarboxylation reaction. Therefore, after the hydrothermal carbonization, the H/C and O/C ratios decreased because of the chemical conversion. Energy retention efficiency suggest that the optimum temperature of hydrothermal carbonization to produce more energy-rich solid fuel is approximately $200^{\circ}C$.

• 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.

• Journal of Soil and Groundwater Environment
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• v.29 no.1
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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.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.11 no.5
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• pp.185-189
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• 2001

Amorphous aluminium phosphate powders were synthesized as a single phase by neutralization reaction of a stoichiometric mixture of $Al_2(SO_4)_3$ and $H_3PO_4$ using the NaOH or KOH solution and subsequently by the hydrothermal precipitation method. The synthesis conditions were as follows : starting materials; $Al_2(SO_4)_3$ and $H_3PO_4$,pH ranges of neutralization reaction; between 5.6 and 6.0, temperature ranges of hydrothermal reaction; between 170 and $180^{\circ}C$,time ranges of hydrothermal reaction; between 4 and 5hs. Under such synthesis conditions, the products are obtained as amorphous aluminium phosphate powders of 0.1~0.3$\mu\textrm{m}$ in size and are Eitted to USP (United Standard Pharmacopoeia) test.

• Applied Chemistry for Engineering
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• v.25 no.6
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• pp.564-569
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• 2014

Zirconia nanoparticles were synthesized by hydrothermal process, and experimental parameters such as reaction temperature, reaction time, kind and concentration of precipitator, kind of precursor were varied. Particle sizes and crystalline phases of each synthesized nanoparticles were analyzed with X-ray diffraction and FE-scanning electron microscope (SEM). The particle size and crystallization of zirconia increased with increasing concentration of precipitator. The growth rate of particle sizes when NaOH as a precipitator was used also increased more than that of KOH. Therefore, the use of KOH rather than NaOH was more effective in the control of particle sizes. An amorphous zirconia nanoparticle was found in 4 h of hydrothermal reaction, but the monoclinic zirconia nanoparticle was found in 8 h and over of hydrothermal reaction, and the width of nanoparticles was slightly slimmed and the length of nanoparticles was slightly extended with increasing reaction time. The smallest particle size was produced at the same synthesis condition when zirconium chloride among the precursors such as zirconium (IV) acetate, zirconium nitrate and zirconium chloride was used.

• 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 $420^{\circ}C$.

• Journal of Industrial and Engineering Chemistry
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• v.68
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• pp.267-273
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• 2018

Hydrothermal liquefaction of Chlorella vulgaris feedstock containing 80% (w/w) water was conducted in a batch reactor as a function of temperature (300, 325 and $350^{\circ}C$) and reaction times (5, 10 and 30 min). The biocrude yield, elemental composition and higher heating value obtained for various reaction conditions helped to predict the optimum conditions for maximizing energy recovery. To optimize the recovery of inorganic nutrients, we further investigated the effect of reaction conditions on the ammonium ($NH_4{^+}$), phosphate ($PO_4{^{3-}}$), nitrate ($NO_3{^-}$) and nitrite ($NO_2{^-}$) concentrations in the aqueous phase. A maximum energy recovery of 78% was obtained at $350^{\circ}C$ and 5 min, with a high energy density of 34.3 MJ/kg and lower contents of oxygen. For the recovery of inorganic nutrients, shorter reaction times achieved higher phosphorus recovery, with maximum recovery being 53% at $350^{\circ}C$ and 5 min. Our results indicate that the reaction condition of $350^{\circ}C$ for 5 min was optimal for maximizing energy recovery with improved quality, at the same time achieving a high phosphorus recovery.

• Journal of Powder Materials
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• v.18 no.1
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• pp.73-77
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• 2011

$Y(OH)_3$ nanowires were synthesized by a hydrothermal reaction of metallic Y with aqueous solution of LiOH. The morphology and the size of the nanowires changed with varying the volume of the LiOH solution inside the autoclave. $Y(OH)_3$ nanowires transformed to $Y_2O_3$ by a subsequent heat-treatment without morphological change. By a proper control of hydrothermal reaction parameter and heat-treatment, the yield of pure $Y_2O_3$ nanowires up to 97% was attained.

• Journal of the Korean Ceramic Society
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• v.45 no.12
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• pp.845-850
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• 2008

Hydrated sodium silicate was synthesized by hydrothermal reaction using anhydrous sodium silicate. The optimum additions of water was 25wt% to make hydrated sodium silicate with homogeneous and purposed water contents. Porous ceramics with homogeneous microstructure and spherical closed pore can be fabricated by elimination of the large pores(a few mm in size) which was formed during first heat treatment through the decomposition of water. Spherical closed pore was formed above $600^{\circ}C$ and the pore size was increased with increasing second heat treatment temperature due to growth of pores. The size of spherical closed pore was varied from 35 to $233\;{\mu}m$ and specific gravity was varied from 0.2 to 1.02 depending on the combinations of the first and second heat treatment temperature.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.17 no.4
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• pp.172-178
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• 2007

Mica (muscovite) powders were synthesized by hydrothermal method (horizontal turning method). The hydrothermal conditions for the synthesis of mica were prepared by the ratio of $K_2O : Al(OH)_3 : SiO_2$ = 1 : 3 : 3 mol% as the starting materials with KOH (8 mol%) solution as the hydrothermal solvent and reaction temperature at $260^{\circ}C$ for 72hrs. The synthetic powder used for preparation of nano silver coated mica by vertical hydrothermal treatment. The hydrothermal conditions for the treated as nano silver coating were prepared by the synthetic powder as raw materials, triple distilled water ($0.5{\ell}$) solution as the hydrothermal solvent with nano silver sol (1,000 ppm) as the material of nano silver coating and reaction temperature at $160{\sim}260^{\circ}C$ for 72 hrs. After hydrothermal treatment, structural, judgment of nano silver coating and character of nano silver coated mica were examined by XRD, SEM, TEM-EDX and shake plask method.