• Korean Journal of Materials Research
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• v.24 no.1
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• pp.53-59
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• 2014

The corrosion resistance of submerged entry nozzle (SEN) materials were investigated for high-class steel manufacturing. Composite samples were fabricated by mixing $ZrO_2$, $Al_2O_3$, MgO, mullite, spinel, and carbon. The raw materials were mixed with attrition milling, compacted in a uniaxial pressure of 200MPa and calcined at $1000^{\circ}C$ for 3 h in $N_2$ atmosphere. The bulk density and apparent porosity of the calcined samples were measured by the liquid displacement method in water using Archimedes's principle. The corrosion resistance of the samples were measured by cup test with mold powder at $1550^{\circ}C$ for 2 h. The microstructure and elemental analysis of samples were observed by scanning electron microscopy (SEM), energy dispersive spectrum (EDS), and X-ray diffraction pattern (XRD). The XRD result shows that the starting raw materials were crystalline phase. The microstructure of fabricated specimen was investigated before and after corrosion tests at $1000^{\circ}C$ and $1550^{\circ}C$ for 2h. $ZrO_2$-C composite showed good resistance in the slag corrosion test. Among the composite oxide materials, $ZrO_2-Al_2O_3$-C and $ZrO_2$-MgO-C showed better resistance than $ZrO_2$-C in the slag corrosion test. The diameter variation index of $ZrO_2$-C refractory was 16.1 at $1000^{\circ}C$ for 2 h. The diameter variation index of the $ZrO_2-Al_2O_3$-C refractory was larger than that of the $ZrO_2$-C refractory at $1550^{\circ}C$ for 2 h.

• Korean Journal of Materials Research
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• v.2 no.5
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• pp.320-329
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• 1992

In 2Y-TZP powders calcined at temperature range of 80$0^{\circ}C$0 to 150$0^{\circ}C$, the effect of stabilization and the transformability of tetragonal phase on the tetragonal to monoclinic transformation have been investigated. The transformability of tetragonal phase in calcined powders shows maximum at the calcination temperature of 130$0^{\circ}C$. This result is explained by a combined effect of the increase of particle size and of constrained force among the particles with increasing the calcination temperature. The amount of transformed monoclinic phase with calcination temperature after quenching in liquid nitrogen, stress induction and isothermal aging at 25$0^{\circ}C$is also explained by the transformability of tetragonal phase determined by the sum of particle size effect and constraint effect.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.139-139
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• 2010

LSM is widely used as a cathode material in SOFC, because of its high electrochemical activity, good stability and compatibility with YSZ electrolyte at high temperature. However, LSM in traditional cathode materials will not generate a satisfactory performance at intermediate temperature. In order to reduce the polarization resistance of cell with the operating temperature of SOFC system, the cathode material of LSCF is one of the most suitable electrode materials because of its high mixed ionic and electronic conductivity. In this report, cathode material, $La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.8}O_3$ powder for intermediate temperature SOFC was synthesized by Pechini method using the starting materials such as nitrate of La, Sr, Co and Fe including ethylene glycol, etc. As a result, the synthesized powder that calcined above $700^{\circ}C$ exhibits successfully perovskite structure, indicating phase-pure of LSCF. Moreover, the particle size, surface area, crystal structure and morphology of the synthesized oxide powders were characterized by SEM, XRD, and BET, etc. In order to evaluate the electrochemical performance for the synthesized powder, slury mixture using the synthesized cathode material was coated by screen-printing process on the anode-supported electrolyte which was prepared by a tape casting method and co-sintering. Finally, electrochemical studies of the SOFC unit cell, including measurements such as power density and impedance, were performed.

• Journal of the Korean Ceramic Society
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• v.39 no.11
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• pp.1103-1107
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• 2002

Biocompatible ${\beta}$-Tricalcium Phosphate(${\beta}$-TCP) powder was successfully synthesized by using a re-cycled eggshell and phosphoric acid. The crystallization behavior of the synthesized powder was dependent on the mixing ratio between the eggshell and phosphoric acid, the starting condition of the eggshell and calcination temperature. The ${\beta}$-TCP was stably synthesized in the 1:1.3~1:1.5 (wt%) mixing ratios of calcined eggshell and phosphoric acid. The synthesis was achieved at about $900{\circ}$ for 1h in an air atmosphere. The crystalline development and microstructure of the synthesized powder were examined by X-ray diffractometer and scanning electron microscopy.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.4
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• pp.106-113
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• 2010

We were tried to draw a conclusions related to additive amount of gypsum in blast furnace slag in the study. In the result, fluidity of concrete decreased with an increase of gypsum and was not satisfied with KS standard in the cases of natural gypsum and limestone sludge more than 2.6% addition. Early compressive strength of concrete containing desulfurized gypsum, fluosilicic acid gypsum and phosphoric acid gypsum were improved respectively but calcined lime sludge and lime powder were not influenced on strength. If available, additive gypsum should be managed less than 2.0% owing to low fluidity. In low temperature, fluosilicic acid gypsum was to advantages on the fluidity while desulfurized gypsum was in high temperature. There also are conclusions that additive gypsum was to be 2.6% in winter and in summer; it's to be fewer than 2.6%.

• Resources Recycling
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• v.10 no.5
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• pp.16-21
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• 2001

Ultrafine $Mg(OH)l_2$and MgO powders were recovered from the waste solution containing $Mg^{++}$ which was a by-product of SHS (Self-propagating High temperature Synthesis)process. The optimum experimental conditions to prepare $Mg(OH)_2$were 13.0 of pH and 0.7M of $Mg^{++}$ content with addition of 9M of KOH as a pH regulator in acid leaching solution. Complete pre-cipitation of Mg(OH)$_2$from $Mg^{++}$ was realized at that condition. The dehydration reaction of the prepared Mg(OH)$_2$was studied by DSC, and the result was used for calcination process. In order to obtain MgO powder, dried Mg(OH)2 powder was calcined at $400~450^{\circ}C$. Particle size and shape of the prepared $Mg(OH)_2$and MgO powder was similar to those of the commercial powders.

• Journal of Powder Materials
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• v.16 no.2
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• pp.115-121
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• 2009

The effects of thermal treatment conditions on ADU (ammonium diuranate) prepared by SOL-GEL method, so-called GSP (Gel supported precipitation) process, were investigated for $UO_2$ kernel preparation. In this study, ADU compound particles were calcined to $UO_3$ particles in air and Ar atmospheres, and these $UO_3$ particles were reduced and sintered in 4%-$H_2$/Ar. During the thermal calcining treatment in air, ADU compound was slightly decomposed, and then converted to $UO_3$ phases at $500^{\circ}C$. At $600^{\circ}C$, the $U_3O_8$ phase appeared together with $UO_3$. After sintering of theses particles, the uranium oxide phases were reduced to a stoichiometric $UO_2$. As a result of the calcining treatment in Ar, more reduced-form of uranium oxide was observed than that treated in air atmosphere by XRD analysis. The final phases of these particles were estimated as a mixture of $U_3O_7$ and $U_4O_9$.

• Journal of the Korean Ceramic Society
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• v.27 no.2
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• pp.201-210
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• 1990

The mullite-15v/o ZrO2 composites were prepared by dispersing ZrO2-3m/o Y2O3 powders into the mullite matrix in order to improve the mechanical properties of the mullite. The densification and retention of t-ZrO2 in the matrix of synthetic mullite were also investigated. From IR spectroscopic analysis, the obtained amorphous SiO2-Al2O3 powder was observed to have Si-O-Al chemical bond in its structure which might result in the homogeneous mullite composition. The lattice parameter of the mullite powder calcined above 130$0^{\circ}C$ (a0=7.5468$\AA$) is nearly close to the value of stoichiometric mullite (71.8wt% Al2O3, a0=7.5456$\AA$). The sintering behavior, microstructure, flexural strength and fracture toughness of the mullite and mullite-15v/o ZrO2 composites have been studied. The mullite-15v/o ZrO2(+3m/o Y2O3) ceramics with relative densities of 96% were obtained when sintered at 1$600^{\circ}C$. The flexural strength and fractrue toughness of the composites sintered at 1$600^{\circ}C$(calcination temperature of mullite powders ; 125$0^{\circ}C$) had maximum values of 307MPa and 2.50MPa.m1/2, respectively. The fracture toughness improvement in the mullite-ZrO2 cmoposite is assumed to be resulted from the combined effect of the stress-induced phase transformation of tetragonal ZrO2 and the crack deflection due to microcracking by the monoclinic ZrO2 formation.

• Journal of the Korean Ceramic Society
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• v.38 no.5
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• pp.401-404
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• 2001

Barium ferrite powders were synthesized by the coprecipitation method using iron-pickling waste acid (IPWA) and BaCl$_2$$.$2H$_2$O as raw materials. Fe$\^$2+/ ions in the IPWA, which contains both Fe$\^$2+/ and Fe$\^$3+/ ions, were oxidized into Fe$\^$3+/ ions using H$_2$O$_2$. Proper amount of BaCl$_2$$.$2H$_2$O was dissolved into the oxidized IPWA. Using NaOH, Ba$\^$2+/ and Fe$\^$3+/ ions were coprecipitated as Ba(OH)$_2$and Fe(OH)$_3$. The coprecipitated Ba(OH)$_2$and Fe(OH)$_3$were washed and dried. Barium ferrite powders were obtained by calcining the dried Ba(OH)$_2$and Fe(OH)$_3$mixture from 400$\^{C}$ to 1000$\^{C}$ with a 100$\^{C}$ interval. Barium ferrite powders were characterized by X-ray diffraction, SEM, and VSM. It was found that barium ferrite powders could be synthesized at around 630$\^{C}$. The synthesized barium ferrite powders showed hexagonal plate shapes with a fairly uniform size. The barium ferrite powder calcined at 900$\^{C}$ showed good magnetic properties, saturation magnetization of 67emu/g and maximum coercivity of 5000 Oe.

• Journal of the Korean Ceramic Society
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• v.56 no.5
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• pp.497-505
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• 2019

Lanthanum-based transition metal cations containing perovskites have emerged as potential catalysts for the intermediate-temperature (600-800℃) oxygen reduction reaction (ORR). Here, we report a facile acetylacetone-assisted combustion route for the synthesis of nanostructured La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF6428) cathodes for intermediate-temperature solid-oxide fuel cells (IT-SOFCs). The as-prepared powder was analyzed by thermogravimetry analysis-differential scanning calorimetry. The powder calcined at 800℃ was characterized by X-ray diffraction, scanning electrode microscopy, energy dispersive X-ray spectroscopy, and Brunauer-Emmett-Teller surface area measurements. It was found that the porosity of the air electrode significantly increased by utilizing the nanostructured LSCF6428 instead of commercial powder. The performance of a single cell fabricated with the nanostructured LSCF6428 cathode increased by 112%, from 0.4 to 0.85 W cm^-2, at 700℃. Electrochemical impedance spectroscopy showed a considerable reduction in the area-specific resistance and activation energy from 133.5 to 61.5 kJ/mol, resulting in enhanced electrocatalytic activity toward ORR and overall cell performance.