• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.5
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• pp.397-403
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• 2003

Microwave dielectric properties of (1-x)ZnW $O_4$-xTi $O_2$ ceramic systems were investigated with calcination temperatures and Ti $O_2$ contents. The ZnW $O_4$ ceramic could be suitably sintered at 1075$^{\circ}C$ and showed the dielectric constant of 13.6, quality factor(Q$\times$ $f_{O}$value) of 22,000 and temperature coefficient of resonant frequency($\tau$$_{f}$) of -65$\pm$2ppm/$^{\circ}C$. Increasing the amount of Ti $O_2$ in the range of 0.25 to 0.45 mol, the dielectric constant and $\tau$$_{f}$ increased due to the role of Ti $O_2$ but the quality factor decreased due to the increase of phase boundaries. The 0.7ZnW $O_4$-0.3Ti $O_2$ ceramic showed the dielectric constant of 19.8, qualify factor(Q$\times$ $f_{0}$) of 20,000 and $\tau$$_{f}$ of -3$\pm$1ppm/$^{\circ}C$.>.EX>.>.>.

• Journal of Korean Society of Water and Wastewater
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• v.34 no.1
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• pp.1-8
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• 2020

In this study, the physicochemical characteristics and fluoride adsorption capacity of the bone char pyrolyzed at different temperatures; 200℃, 300℃, 350℃, 400℃, 500℃, 600℃, and 700℃ were investigated. Analytical studies of the synthesized bone char including; SEM-EDS, XRD, BET and FT-IR, showed the presence of hydroxyapatite(HAP), which is the main substance that adsorbs fluoride from aqueous solutions containing high fluoride concentrations. Bone char pyrolyzed from 350~700℃ specifically revealed that, the lower the temperature, the higher the fluoride adsorption capacity and vice versa. The loss of the fluoride adsorption function of HAP (OH^- band in the FTIR analysis) was interpreted as the main reason behind this inverse correlation between temperature and fluoride adsorption. Bone char produced at 350℃ hence exhibited a fluoride adsorption capacity of 10.56 mgF/g, resulting in significantly higher adsorption compared to previous studies.

• Korean Journal of Chemical Engineering
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• v.35 no.12
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• pp.2365-2378
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• 2018

We investigated the correlation between vanadium surface density and VOx structure species in the selective catalytic reduction of NOx by $NH_3$. The properties of the $VOx/TiO_2$ catalysts were investigated using physicochemical measurements, including BET, XRD, Raman spectroscopy, FE-TEM, UV-visible DRS, $NH_3-TPD$, $H_2-TPR$, $O_2-On/Off$. Catalysts were prepared using the wet impregnation method by supporting 1.0-3.0 wt% vanadium on $TiO_2$ thermally treated at various calcination temperatures. Through the above analysis, we found that VOx surface density was $3.4VOx/nm^2$, and the optimal V loading amounts were 2.0-2.5 wt% and the specific surface area was $65-80m^2/g$. In addition, it was confirmed that the optimal VOx surface density and formation of vanadium structure species correlated with the reaction activity depending on the V loading amounts and the specific surface area size.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.25 no.4
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• pp.166-171
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• 2015

In this study, using solid-state and flux, $Y_3Al_5O_{12}:Er^{3+}\;(YAG:Er^{3+})$ powders were successfully synthesized at low temperatures. To analyze the crystallinity of powders according to the synthesis or non-synthesis of powders and powder calcination temperatures, X-ray diffraction (XRD) was measured. In the case of pure YAG, when YAG was analyzed using the general solid-phase method, it was calcined for 12 hours at $1400^{\circ}C$ and pure YAG phase could be obtained. But when $BaF_2$ was added to YAG, YAG was synthesized at lower temperature (1000^{\circ}C$). It was thus found that the synthesis temperature could be lowered by about $400^{\circ}C$. Also, when BaF2 with an optimal concentration was added to $YAG:Er^{3+}$, the particle shape and size according to synthesis temperatures were surveyed, and corresponding luminous intensity was discussed.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.4
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• pp.166-173
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• 2021

The rutile phase of TiO₂ forms a stable phase at high temperatures compared to anatase phase, but the stable temperature range of anatase changes depending on the synthesis conditions. In this study, nano-sized TiO₂ was synthesized by the Sol-gel method using TiOSO₄ and a mixed solvent of ethanol and distilled water, and the phase change of anatase and rutile according to pH and heat treatment temperature was investigated. Changes in the ratio of anatase and rutile were observed by changing the pH (3, 5, 7, 9) and heat treatment temperature (500, 600, 700, 800, 900℃) conditions of the prepared TiO₂. As a result of observing these changes through XRD and FE-SEM analysis, anatase TiO₂ at 500℃ and rutile TiO₂ at 900℃ were observed. According to the pH, at these intermediate temperatures of 600, 700 and 800℃, the ratio of anatase and rutile changes. At 700℃, it was concluded that pH = 3~5 had a larger ratio of anatase TiO₂, and pH = 7~9 had a larger ratio of rutile TiO₂.

• Korean Journal of Materials Research
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• v.34 no.4
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• pp.185-193
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• 2024

In this study, NASICON-type Li_1+XGa_XTi_2-X(PO₄)₃ (x = 0.1, 0.3 and 0.4) solid-state electrolytes for all-solid-state batteries were synthesized through the sol-gel method. In addition, the influence on the ion conductivity of solid-state electrolytes when partially substituted for Ti⁴⁺ (0.61Å) site to Ga³⁺ (0.62Å) of trivalent cations was investigated. The obtained precursor was heat treated at 450 ℃, and a single crystalline phase of Li_1+XGa_XTi_2-X(PO₄)₃ systems was obtained at a calcination temperature above 650 ℃. Additionally, the calcinated powders were pelletized and sintered at temperatures from 800 ℃ to 1,000 ℃ at 100 ℃ intervals. The synthesized powder and sintered bodies of Li_1+XGa_XTi_2-X(PO₄)₃ were characterized using TG-DTA, XRD, XPS and FE-SEM. The ionic conduction properties as solid-state electrolytes were investigated by AC impedance. As a result, Li_1+XGa_XTi_2-X(PO₄)₃ was successfully produced in all cases. However, a GaPO₄ impurity was formed due to the high sintering temperatures and high Ga content. The crystallinity of Li_1+XGa_XTi_2-X(PO₄)₃ increased with the sintering temperature as evidenced by FE-SEM observations, which demonstrated that the edges of the larger cube-shaped grains become sharper with increases in the sintering temperature. In samples with high sintering temperatures at 1,000 ℃ and high Ga content above 0.3, coarsening of grains occurred. This resulted in the formation of many grain boundaries, leading to low sinterability. These two factors, the impurity and grain boundary, have an enormous impact on the properties of Li_1+XGa_XTi_2-X(PO₄)₃. The Li_1.3Ga_0.3Ti_1.7(PO₄)₃ pellet sintered at 900 ℃ was denser than those sintered at other conditions, showing the highest total ion conductivity of 7.66 × 10^-5 S/cm at room temperature. The total activation energy of Li-ion transport for the Li_1.3Ga_0.3Ti_1.7(PO₄)₃ solid-state electrolyte was estimated to be as low as 0.36 eV. Although the Li_1+XGa_XTi_2-X(PO₄)₃ sintered at 1,000 ℃ had a relatively high apparent density, it had less total ionic conductivity due to an increase in the grain-boundary resistance with coarse grains.

• Applied Chemistry for Engineering
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• v.7 no.2
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• pp.261-268
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• 1996

Various $Cu/SiO_2$ catalysts with copper concentration ranging from 0 to 50wt% were prepared by kneading method for the steam reforming of methanol. These catalysts were calcined at temperatures in the range of $400^{\circ}C{\sim}900^{\circ}C$ and then reduced in a $H_2$ atmosphere in the range of $150^{\circ}C{\sim}350^{\circ}C$. Steam reforming of methanol was carried out at atmospheric pressure over a temperature range of $200^{\circ}C{\sim}400^{\circ}C$, steam/methanol molar ratio of 0.4~1.6 and W/F of 3~25 g.-cat.hr./mol. Characterization of the catalysts was studied using IR, BET and XRD. Using copper nitrate as a precursor for catalysts, pH in the preparation of catalysts had a great effect on the catalytic activity, but pH in the preparation of catalysts, calcination temperature, and reducing temperature in $H_2$ atmosphere had no effect on the product distribution. Optimum copper concentration, calcination temperature and reducing temperature were 40wt%, $700^{\circ}C$ and $300^{\circ}C$, respective)y. Reaction temperature for maximum $H_2$ production was $275^{\circ}C$, and the formation of methane which lowered quantity and quality of $H_2$ would be inhibited below $275^{\circ}C$. $Cu^{\circ}-Cu_2O$ might be active species in $Cu/SiO_2$ catalyst.

• Korean Journal of Materials Research
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• v.2 no.1
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• pp.3-11
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• 1992

Aluminum sulfate hydrate was prepared using sulfuric acid from Ha-dong kaolin. The effects of calcination-temperature and calcination-time of kaolin, reaction-temperature and reaction-time, and sulfuric acid concentration on the formation of aluminum sulfate hydrate were investigated. The precipitation condition of aluminum sulfate hydrate from sulfuric acid solution was determined. Also, the products heat-treated at different temperatures have been investigated by X-ray diffraction, thermogravimetry, differential thermal analysis, Fourier transform infrared spectrophotometer, scanning electron microscopy, particle size distribution analysis and chemical analysis. In the optimum condition, the conversion of aluminum oxide in kaolin to aluminum sulfate hydrate was 60%. From the results of XRD, TG-DTA, and FT-IR, it is suggested that the aluminum sulfate hydrate is thermally decomposed as follows ; $Al_2(SO_4)_3{\cdot}18H_2O{\rightarrow}Al_2(SO_4)_3{\cdot}6H_2O{\rightarrow}Al_2(SO_4){\rightarrow}\;amorphous\;alumina{\rightarrow}{\gamma}-alumina{\rightarrow}{\delta}-alumina{\rightarrow}{\theta}-alumina{\rightarrow}{\alpha}-alumina$. The purity of alumina powder prepared by calcining aluminum sulfate hydrate at $1200^{\circ}C$ was 99.99 percent.

• Korean Journal of Materials Research
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• v.29 no.2
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• pp.92-96
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• 2019

Transition metal oxide is widely used as a water electrolysis catalyst to substitute for a noble metal catalyst such as $IrO_2$ and $RuO_2$. In this study, the sol-gel method is used to synthesize the $Cu_xCo_{3-x}O_4$ catalyst for the oxygen evolution reaction (OER),. The CuxCo3-xO4 is synthesized at various calcination temperatures from $250^{\circ}C$ to $400^{\circ}C$ for 4 h. The $Cu_xCo_{3-x}O_4$ synthesized at $300^{\circ}C$ has a perfect spinel structure without residues of the precursor and secondary phases, such as CuO. The particle size of $Cu_xCo_{3-x}O_4$ increases with an increase in calcination temperature. Amongst all the samples studied, $Cu_xCo_{3-x}O_4$, which is synthesized at 300?, has the highest activity for the OER. Its onset potential for the OER is 370 mV and the overpotential at $10mA/cm^2$ is 438 mV. The tafel slope of $Cu_xCo_{3-x}O_4$ synthesized at $300^{\circ}C$ has a low value of 58 mV/dec. These results are mainly explained by the increase in the available active surface area of the $Cu_xCo_{3-x}O_4$ catalyst.

• Journal of the Korean Electrochemical Society
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• v.10 no.4
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• pp.288-294
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• 2007

The LSCF cathode far Solid Oxide Fuel Cell was investigated to develop high performance unit cell at intermediate temperature by modified oxalate method with different electrolytes and different pH. The LSCF powders employed La, Sr, Co and Fe oxides, oxalic acid, ethanol and $NH_4OH$ solution were synthesized with pH controlled as 2, 6, 7, 8, 9 and 10 at $80^{\circ}C$ Single crystalline phase was obtained from pH $2{\sim}9$. on the other hand, $La_2O_3$ appeared from pH 10. Very fine powder with particle size of 50 nm was obtained at calcination temperature of $800^{\circ}C$ for 4 hours. LSCF cathode synthesized at pH 7 showed the highest electric conductivity in the temperature range of $600^{\circ}C$ to $900^{\circ}C$ its value was 950 S/cm at $900^{\circ}C$ Under same synthesis conditions, polarization resistance of each LSCF cathode was changed with different calcination temperatures. As-prepared powder presented 2.52, 1.54 and $2.58\;{\Omega}$ at $600^{\circ}C$ with ScSZ, 8Y-YSZ and GDC as its electrolyte respectively after calcination at $800^{\circ}C$ for 4 hours.