• Journal of Magnetics
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• v.22 no.2
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• pp.169-174
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• 2017

In this work, lithium ferrite ($Li_{0.5}Fe_{2.5}O_4$) nanoparticles were prepared via mechanochemical processing and subsequent heat treatment at a relatively low ($600^{\circ}C$) calcining temperature. The raw materials used were high purity $Fe_2O_3$ and $Li_2CO_3$ that were milled for between 2 and 20 h. The milled powders were then calcined at temperatures of 500 and $600^{\circ}C$ for 5 h in air. XRD results show that optimum conditions to obtain single phase lithium ferrite nanoparticles with a mean crystallite size of about 23 nm, using Scherrer's formula, are 10 h milling and calcination at $600^{\circ}C$. Saturation magnetization and coercivity of the single phase Li ferrite nanoparticles are 44.6 emu/g and 100 Oe respectively, which are both smaller than those of the bulk Li ferrite. The Curie temperature of the single sample was determined by a Faraday balance, which is $578^{\circ}C$ and smaller than that of bulk Li ferrite.

• Korean Journal of Materials Research
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• v.23 no.10
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• pp.543-549
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• 2013

The purpose of this paper was to investigate the effect of a high-energy milling (HEM) process on the particle morphology and the correlation between a thermal treatment and tetragonal/monoclinic nanostructured zirconia powders obtained by a precipitation process. To eliminate chloride residue ions from hydrous zirconia, a modified washing method was used. It was found that the used washing method was effective in removing the chloride from the precipitated gel. In order to investigate the effect of a pre-milling process on the particle morphology of the precipitate, dried $Zr(OH)_4$ was milled using a HEM machine with distilled water. The particle size of the $Zr(OH)_4$ powder exposed to HEM reduced to 100~150 nm, whereas that of fresh $Zr(OH)_4$ powder without a pre-milling process had a large and irregular size of 100 nm~1.5 ${\mu}m$. Additionally, modified heat treatment process was proposed to achieve nano-sized zirconia having a pure monoclinic phase. It was evident that two-step calcining process was effective in perfectly eliminating the tetragonal phase, having a small average particle of ~100 nm with good uniformity compared to the sample calcined by a single-step process, showing a large average particle size of ~300 nm with an irregular particle shape and a broad particle size distribution. The modified method is considered to be a promising process for nano-sized zirconia having a fully monoclinic phase.

• Journal of the Korean Chemical Society
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• v.63 no.6
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• pp.440-445
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• 2019

It has developed a method that can recover efficiently the reproducible resources from the vehicle waste lithium second battery module. Module cell consists of copper thin film, aluminum thin film and diaphragm made with polymer between these thin films. Cell was disassembled completely without any damage in glove box and through several steps. Preferentially, cathode active material was separated from aluminum thin film at heat treatment of 400 ℃. The retrieved cathode active material was then obtained as high purity after calcining at 800 ℃ to remove residual carbon. Based on this study, it was found that rare metals such as Co, Ni, Mn and Li made up of cathode active material could recover above 80% from aluminum thin film.

• Journal of the Korean Ceramic Society
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• v.46 no.6
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• pp.574-582
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• 2009

$UO_2$ microsphere particles, core material of HTGR(High Temperature Gas Reactor) nuclear fuel, were prepared using by the GSP(Gel Supported Precipitation) method which is a modified-method of the wet sol-gel process. The spherical shape of initial liquid ADU droplets from the vibration nozzle system was continuously kept till the conversion to the final $UO_2$ microsphere. But the size of a final $UO_2$ microsphere was shrunken to about 25% of an initial ADU droplet size. Also, we found that the composition of dried-ADU gel particles was constituted of the very complicated phases, coexisted the U=O, C-H, N-H, N-O, and O-H functional groups by FT-IR. The important factors for obtain the no-crack $UO_2$ microsphere during the thermal treatment processes must perfectly wash out the remained-$NH_4NO_3$ within the ADU gel particle in washing process and the selections of an appropriate heating rate at a suitable gas atmosphere, during the calcining of ADU gel particles, the reducing of $UO_3$ particles, and the sintering of $UO_2$ particles, respectively.

• Applied Chemistry for Engineering
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• v.3 no.4
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• pp.663-669
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• 1992

Chromium oxide/zirconia catalysts were prepared by dry impregnation of $Zr(OH)_4$ powder with aqueous solution of $(NH_4)_2CrO_4$ followed by calcining in air. The redox behavior of prepared catalysts were investigated by reacting cumene as test material over catalysts. As a result it was found that $Cr^{6+}$ species(as chromate) on the surface of catalyst was responsible for the formation of strong acid site and the catalytic activity for the dealkylation of cumene. However, much of the $Cr^{6+}$ species was reduced to $Cr^{3+}$ species by $H_2$ formed during the catalytic reaction of cumene and the reduced $Cr^{3+}$ species was an active site for dehydrogenation of cumene to form ${\alpha}$-methyl styrene. The reduced $Cr^{3+}$ species was also reoxidized to a $Cr^{6+}$ species after treatment with $O_2$ and consequently the deoxidized catalyst exhibited catalytic activity for the dealkylation reaction of cumene.

• Applied Chemistry for Engineering
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• v.8 no.2
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• pp.332-338
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• 1997

$SnO_2$ as raw material of sensor for $NO_2$ detection was prepared by precipitating $SnCl_4$ solution with aqueous ammonia followed by calcining in air. The characterization of $SnO_2$ was carried out using FT-IR and XRD, and $SnO_2$ thick film sensor was fabricated by screen-printing method. The particle size of $SnO_2$ calcined at higher temperature increased due to the growth of crystalline. $SnO_2$ sensor fabricated by using $SnO_2$ sample calcined at $1000^{\circ}C$ followed by heat treatment at $700^{\circ}C$ exhibited excellent sensing characteristics and selectivity for $NO_2$ gas at the operating temperature of $250^{\circ}C$.

• Progress in Superconductivity
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• v.7 no.2
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• pp.135-139
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• 2006

We fabricated YBCO coated conductors (CCs) by TFA-MOD process and evaluated microstructure, texture formation, and critical temperature ($T_c$) and current ($I_c$). YBCO precursor solution was synthesized using metal-trifluoroacetates and dip coated on $LaAlO_3$(LAO) substrate. The phase formation and microstructure was characterized by X-ray diffraction and scanning electron microscopy (SEM) and the degree of texture was evaluated by pole-figure analysis. The CC was heat-treated in various calcining temperatures ($370^{\circ}C-460^{\circ}C$) and firing temperatures ($750^{\circ}C-800^{\circ}C$). As fired at $775^{\circ}C$ for 4h, the CC had the highest $T_c$ of 89.5 K and $I_c$ of 40 A/cm-width ($J_c=2.0\;MA/cm^2$). Microstructural observation indicated that the YBCO film was dense and homogeneous and had a strong cube texture without formation of second phase and its in-plane full-width at half-maxima; $5.2^{\circ}$ under optimum condition.

• Progress in Superconductivity
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• v.9 no.2
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• pp.167-172
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• 2008

We fabricated $YBa_2Cu_3O_{7-x}$(YBCO) films on (00l) $LaAlO_3$ substrates prepared by metal organic deposition(MOD) method using trifluoroacetate(TFA) solution. The films with various thicknesses were prepared by repeating the dip-coating and calcining processes. The effects of film thickness on phase formation, microstructures, and critical properties were evaluated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The microstructure and resultant critical current($I_C$) and critical current density($J_C$) varied remarkably with film thickness: The ($I_C$) value increased from 39 to 160 A/cm-width as the number of coatings increased from one to four, while the corresponding $J_C$ was measured to be in the range of $0.84-1.21\;MA/cm^2$. Both the $I_C$ and $J_C$ decreased when an additional coating was applied due to microstructural degradation, indicating that the optimum thickness is in the range of $1.1-1.8\;{\mu}m$. The possible cause for the decrease in the $I_C$ and $J_C$ value for film thicker than $1.8\;{\mu}m$ include non-uniform thickness, increased surface roughness, and the poor formability of the YBCO phase and texture arising from the insufficient heat treatment time with respect to the increased thickness.

• Journal of the Korean Ceramic Society
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• v.38 no.9
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• pp.794-798
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• 2001

$Y_{2-x}SiO_5:Ce_x^{3+}$(x=0.002∼0.04) phosphors were prepared by sol-gel process, amorphous crystal phase was observed in calcining dry gel at 800$^{\circ}$C, but pure $X_2$ type of type $Y_2SiO_5$ phase appeared from heat treatment above 1000$^{\circ}$C. Light absorption of tye $Y_2SiO_5$ host lattice occurred at 230∼360nm, and light absorption of the $Y_{2-x}SiO_5:Ce_x^{3+}$ phosphors was observed at 300∼400nm in adding $Ce^{3+}$. $Y_{2-x}SiO_5:Ce_x^{3+}$ phosphors showed maximum emission shoulder at 436nm. Maximum CL intensities of $Y_{2-x}SiO_5:Ce_x^{3+}$ were observed in adding 0.025 $Ce^{3+}$ and the phosphor showed x=0.161, y=0.124 in color coordinate of CIE1931.

• Journal of Environmental Science International
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• v.27 no.2
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• pp.109-122
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• 2018

This study was conducted to investigate the removal characteristics of heavy metals and sulfate ion from acid mine drainage by porous zeolite-slag ceramics (ZS ceramics) that was prepared by adding wood flour as pore-foaming agent while calcining the mixtures of natural zeolite and converter slag. The batch test showed that the removal efficiency of heavy metals by pellet-type porous ZS ceramics increased as the particle size of wood flour was decreased and as the weight mixing ratio of wood flour to ZS ceramics was increased. The optimal particle size and weight mixing ratio of wood flour were measured to be $75{\mu}m$ and 7~10%, respectively. The removal test with the porous ZS ceramics prepared in these optimal condition showed very high removal efficiencies: more than 98.4% for all heavy metals and 73.9% for sulfate ion. Relative to nonporous ZS ceramics, the increment of removal efficiency of heavy metals by porous ZS ceramics with $75{\mu}m$ and 10% wood flour was 5.8%, 60.5%, 36.9%, 87.7%, 10.3%, and 57.4% for Al, Cd, Cu, Mn, Pb, and Zn, respectively. The mechanism analysis of removal by the porous ZS ceramics suggested that the heavy metals and sulfate ion from acid mine drainage are eliminated by multiple reactions such as adsorption and/or ion exchange as well as precipitation and/or co-precipitation.