• Korean Journal of Materials Research
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• v.17 no.10
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• pp.526-531
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• 2007

The sintering behavior and electrical property of $Ce_{0.8}Gd_{0.2}O_{1.9}$ ceramics were investigated with the iron oxide concentration ranging from 0 to 5 mol%. Both the sintered density and grain size were found to increase up to 2 mol% $Fe_2O_3$, and then to decrease with further additions. At a higher $Fe_2O_3$ content above 3 mol%, grain size decreased by a pinning effect induced by different shape grains. The electrical conductivity was also increased with increasing $Fe_2O_3$ content up to 2 mol%. Total conductivity of 2 mol% $Fe_2O_3-added$ specimen showed the maximum conductivity of $2{\times}10^{-2}{\Omega}{\cdot}cm^{-1}$ at $500^{\circ}C$. The addition of $Fe_2O_3$ was found to promote the sintering properties and electrical conductivities of $Gd_2O_3-dope\;CeO_2$.

• Journal of Korean Society of Environmental Engineers
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• v.27 no.5
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• pp.513-518
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• 2005

Catalytic oxidation of toluene on the manganese oxide catalysts and manganese-cerium oxide catalysts was investigated. The catalysts were characterised by X-ray diffraction(XRD), thermo gravimetric analyzer(TGA), toluene-temperature program reduction(Toluene-TPR). We found that the optimal manganese content was 18.2 wt.% and the optimal cerium content was 10.0 wt.% at catalytic oxidation of toluene. It is shown that ceria improves the activity of manganese oxide phases. From the XRD results, it was estimated that $MnO_2$ phase was active site in the monometallic and bimetallic catalysts. From the TGA and Toluene-TPR results, it show that ceria improves the mobility of the lattice oxygen, adequate oxidation state of the active phase, reduction ability at low temperature, and re-oxidation of the active site.

• Journal of the Korean Ceramic Society
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• v.35 no.12
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• pp.1294-1300
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• 1998

Yttria-stabilized zirconia ceramics with irregular grain shapes and curved grain boundaries was prepared by ceria doping. The amount of ceria doped into zirconia compacts by a dipping method were at range of 2 to 20 mol% Irregular grain shapes and curved grain boundaries were formed only inspecimens doped with more than 8mol% cerial. Ceria-doped specimens showed large grain size and low sintered density compared with pure yttria-stabilized zirconia which was due to the increase in the contents of stabilizer and cubic phase. The amount of doped ceria was larger on the surface than the inside regions and therefore mi-crostructure and phase on the surface were different from those in the inside regions. Transgranular frac-ture mode was observed ion ceria doped specimens due to irregular large grain sizes.

• Transactions of the Korean hydrogen and new energy society
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• v.23 no.6
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• pp.640-646
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• 2012

The effect of Ce promotion over 1wt% $Pt/{\gamma}-Al_2O_3$ catalysts on the CO conversion and $CO_2$ selectivity was investigated in preferential CO oxidation (PrOx) to reduce the CO concentration less than 10 ppm in excess $H_2$ stream for polymer electrolyte membrane fuel cell (PEMFC). Ce-promoted 1wt% $Pt/{\gamma}-Al_2O_3$ catalysts were prepared by incipient wetness impregnation method and the loading amount of Pt was fixed at 1wt%. The content of Ce promoter which has excellent oxygen storage and transfer capability due to the redox property was adjusted from 0 to 1.5wt%. Ce-promoted 1wt% $Pt/{\gamma}-Al_2O_3$ catalysts exhibit high CO conversion and $CO_2$ selectivity at low temperatures below $150^{\circ}C$ due to the improvement of reducibility of surface PtOx species compared with the 1wt% $Pt/{\gamma}-Al_2O_3$ catalyst without Ce addition. When Ce content was more than 1wt%, the catalytic activity was decreased at over $160^{\circ}C$ in PrOx because of competitive $H_2$ oxidation. As a result, 0.5wt% Ce is optimal content not only to achieve high catalytic activity and good stability at low temperatures below $150^{\circ}C$ in the presence of $CO_2$ and $H_2O$ but also to minimize the $H_2$ oxidation at high temperatures.

• Journal of the Korean Ceramic Society
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• v.32 no.1
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• pp.95-105
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• 1995

Ceria(CeO2) stabilized zirconia(CeSZ) sol was synthesized with zirconium n-butoxide Zr(OC4H9)4 and cerium nitrate hexahydrate Ce(NO3)3.6H2O as precursors and ethylacetoacetate(EAcAc) as a chelating agent under atmosphere. CeSZ films were deposited on AISI 304 stainless steel using the prepared polymeric sol by dipcoating and the coating characteristics were investigated by XRD, ellipsometry, scratch test and SEM. The CeSZ film began to crystallize from amorphous to tetragonal phase at 40$0^{\circ}C$ and it was not converted into monoclinic phase up to 100$0^{\circ}C$ by the addition of 16mol% CeO2 as a stabilizer which could suppress phase transformation of zirconia. The CeSZ films were prepared by varying the EAcAc contents and the cncentration of CeSZ sol and measured the thickness and refractive index. From these results, it was found that the EAcAc contents and concentration of CeSZ coating sol evidently affect the densification of CeSZ film. The CeSZ film coated with 0.4M CeSZ sol and heat-treated at $600^{\circ}C$ for 10min had thickness of 50nm and 17% porosity. The CeSZ film on 304 stainless steel effectively acted as a protective layer against oxidation up to 80$0^{\circ}C$ and had superior corrosion resistance in 25% H2SO4 solution for 4.5 hrs.

• Korean Journal of Materials Research
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• v.25 no.3
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• pp.144-148
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• 2015

Cubic mesocrystal $CeO_2$ was synthesized via a hydrothermal method with glutamic acid ($C_5H_9NO_4$) as a template. The XRD pattern of a calcined sample shows the face-centered cubic fluorite structure of ceria. Transmission electron microscopy (TEM) and the selected-area electron diffraction (SAED) pattern revealed that the submicron cubic mesocrystals were composed of many small crystals attached to each other with the same orientation. The UV-visible adsorption spectrum exhibited the red-shift phenomenon of mesocrystal $CeO_2$ compared to commercial $CeO_2$ particles; thus, the prepared materials show tremendous potential to degrade organic dyes under visible light illumination. With a concentration of a rhodamine B solution of 20 mg/L and a catalyst amount of 0.1 g/L, the reaction showed higher photocatalytic performance following irradiation with a xenon lamp (${\geq}380nm$). The decoloring rate can exceed 100% after 300 min.

• Korean Chemical Engineering Research
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• v.49 no.6
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• pp.781-785
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• 2011

In this work, a nano-sized samaria-doped ceria(SDC) was prepared by a urea-based hydrothermal method and characterized by XRD, FESEM and TEM. It was observed that the increase in synthesis time and temperature gave rise to crystallity and particles size. Moreover, the synthesised powders had a excellent ion-conductivity(0.1 S/cm at 600~$800^{\circ}C$) which is suitable for electrolyte of intermediate temperature-solid oxide fuel cell(IT-SOFC). Subsequently for use as electrolyte for anode-supported IT-SOFC, we tried to deposit the SDC powder on a porous NiO-SDC substrate by electrophoretic deposition(EPD) method. From the FESEM observation, a compact

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.2
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• pp.145-152
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• 2006

The densification behavior and electrical conductivity of $Ce_{0.8}Gd_{0.2}O_{1.9}$ ceramics were investigated with the strontium gallate concentration ranging from 0 to $5\;mol\%$. Both the sintered density and grain size were found to increase rapidly up to $0.5\;mol\%$ $Sr_2Ga_2O_5$, and then to decrease with further addition. Dense $Ce_{0.8}Gd_{0.2}O_{1.9}$ ceramics with $97\%$ of the theoretical density could be obtained for $0.5\;mol\%$ $Sr_2Ga_2O_5$-added specimen sintered at $1250^{\circ}C$ for 5 h, whereas pure $Ce_{0.8}Gd_{0.2}O_{1.9}$ ceramics needed to be sintered at $1550^{\circ}C$ in order to obtain an equivalent theoretical density, Electrical conductivity was measured as a function of dopant content, over the temperature range of $350\;-\;600^{\circ}C$ in air. Total conductivity of $0.5\;mol\%$ $Sr_2Ga_2O_5$-added specimen showed the maximum conductivity of $2.37{\times}10^{-2}{{\Omega}-1}{\cdot}cm^{-1}$ at $500^{\circ}C$, The addition of strontium gallate was found to promote the sintering properties and electrical conductivities of $Gd_2O_3$-doped $CeO_2$.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.416-417
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• 2006

Nanostructured ceria powder was synthesized by a thermochemical process and investigated its applicability for an oxygen gas sensor. An amorphous precursor powders prepared by spray drying a cerium-nitrate solution were transformed successfully into nanostructured ceria by heat-treatment in air atmosphere. The powders were a loose agglomerated structure with extremely fine $CeO_2$ particles about 15 nm in size, resulting in a very high specific surface area $(110\;m^2/g)$. The oxygen sensitivity and the response time $t_{90}$ measured at sintered sample at $1000^{\circ}C$ was about -0.25 and very short, i.e., $3{\sim}5$ seconds, respectively.

• Journal of the Korean Ceramic Society
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• v.45 no.12
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• pp.782-787
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• 2008

Ni-ceria cermets have been extensively investigated as candidates for the anode in intermediate-temperature solid oxide fuel cells. We have used the citric method to synthesize nanocomposite powders consisting of NiO (Ni metal content: $40{\sim}60%$ by volume) highly dispersed in $Ce_{0.9}Gd_{0.1}O_{1.95}$ (CGO). The microstructure characteristics and sintering behaviors of the nanocomposites were investigated. No impurity phases were observed and the shrinkage of these substrates matched well with that of a CGO electrolyte with a specific surface area of $11\;m^2/g$. Densification of the CGO electrolyte layer to $<5\;{\mu}m$ thickness was achieved by co-firing the laminated electrolyte with the porous NiO-CGO substrate at $1400^{\circ}C$ for 6 h.