• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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• pp.140-140
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• 2003

$UO_2$-5wt%CeO$_2$ 분말에 첨가제 Li$_2$O을 첨가하여 소결분위기, 온도 및 첨가량이 소결체의 치밀화와 결정립성장에 미치는 영향을 조사하였으며, $UO_2$-5wt%CeO$_2$소결체의 산화에 의한 분말화 거동을 산화조건에 따라 측정하여 이를 $UO_2$소결체의 분말화 및 산화거동과 비교 분석하였고, 불량 scrap 소결체를 재사용하기 위해 산화실험에서 얻은 최적 산화조건으로 소결체를 분말화하여 원료분말에 첨가, 분말처리후 소결하여 이것이 소결체의 특성에 미치는 영향을 분석하였다. $UO_2$-5wt%CeO$_2$에 Li$_2$O를 첨가하여 소결할 경우, 온도에 대한 영향은 크지 않았으나 첨가량 및 분위기에 따른 치밀화와 결정립성장이 다르게 나타났다. 산화실험에서는 $UO_2$-5wt%CeO$_2$ 혼합소결체시료가 $UO_2$보다 산화에 필요한 유도시간이 길게 나타났으며, 산화온도가 증가함에 따라 무게증가는 감소하였다. 분말처리에서 혼합-분쇄한 경우에는 scrap 첨가량에 따라 밀도는 감소하나, 결정립이 성장하였으며, 전체 기공분율은 증가하였다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11b
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• pp.430-433
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• 2001

The $0.96MgTiO_{3}-0.04SrTiO_{3}+xCe(x=0{\sim}1.6wt%)$ ceramics were fabricated by the conventional mixed oxide method. The sintering temperature and time were $1300^{\circ}C$, 2hr., respectively. From the X-ray diffraction patterns, it was found that the perovskite $SrTiO_{3}$ and ilmenite $MgTiO_{3}$ structures were coexisted in the $0.96MgTiO_{3}-0.04SrTiO_{3}+xCe(x=0{\sim}1.6wt%)$ ceramics. The dielectric constant$(\varepsilon_{r})$ was increased with addition of Ce. The temperature coefficient of resonant frequency$(\Gamma_{f})$ was gradually varied from positive value to the negative value with increasing the Ce. The temperature coefficient of resonant frequency of the $0.96MgTiO_{3}-0.04SrTiO_{3}+0.2Ce$ ceramics was near zero, where the dielectric constant, quality factor, and $\Gamma_{f}$ were 20.68, 50,272 and ${-0.5ppm/^{\circ}C}$, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11a
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• pp.430-433
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• 2001

The 0.96MgTiO$_3$-0.04SrTiO$_3$+xCe(x=0∼1.6 wt%) ceramics were fabricated by the conventional mixed oxide method. The sintering temperature and time were 1300$^{\circ}C$, 2hr., respectively. From the X-ray diffraction patterns, it was found that the perovskite SrTiO$_3$ and ilmenite MgTiO$_3$ structures were coexisted in the 0.96MgTiO$_3$-0.04SrTiO$_3$+xCe(x=0∼1.6 wt%) ceramics. The dielectric constant($\varepsilon$$\sub$r/) was increased with addition of Ce. The temperature coefficient of resonant frequency($\tau$$\sub$f/) was gradually varied from positive value to the negative value with increasing the Ce. The temperature coefficient of resonant frequency of the 0.96MgTiO$_3$-0.04SrTiO$_3$+0.2Ce ceramics was near zero, where the dielectric constant, quality factor, and $\tau$$\sub$f/ were 20.68, 50, 272 and -0.5pm/$^{\circ}C$, respectively.

• Journal of Hydrogen and New Energy
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• v.18 no.1
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• pp.32-39
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• 2007

CO oxidation and selective CO oxidation of $La_xCe_{1-x}Co_yCu_{1-y}O_{3-{\alpha}}$ perovskite(x=1, 0.9, 0.7. 0.5; y=1, 0.9, 0.7, 0.5) were investigated. For CO oxidation, catalytic activities were studied according to different preparation conditions such as pH and calcination temperature. The influence of the change of the $O_2$ concentration for selective CO oxidation was studied, too. The substitution of Ce for La improved the catalytic activity for CO oxidation and selective CO oxidation and best activity was observed for $La_{0.7}Ce_{0.3}CoO_3$ prepared at pH 11 and calcined at $600^{\circ}C$. The temperature of 90% CO conversion for CO oxidation using $La_{0.7}Ce_{0.3}CoO_3$ was $230^{\circ}C$. In contrast to the enhancement effect by Ce substitution, the partial substitution of Cu for Co in $LaCo_yCu_{1-y}O_{3-{\alpha}}$ decreased catalytic activities for CO oxidation reaction compared to that using $LaCoO_3$. For selective CO oxidation, the best CO conversion was 66% at $230^{\circ}C$ for $La_{0.7}Ce_{0.3}CoO_3$. The CO conversion of $La_{0.7}Ce_{0.3}CoO_3$ was greatly increased from 66% to 91% as increasing $O_2$ concentration from 1% to 2%.

• Advances in materials Research
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• v.3 no.2
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• pp.105-116
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• 2014

The microwave dielectric properties of $CeO_2$ nanoparticles (0.5, 1.0 & 1.5wt%) doped $Mg_2TiO_4$ (MTO) ceramics have been investigated at cryogenic temperatures. The XRD patterns of the samples were refined using the full proof program reveal the inverse spinel structure without any secondary phases. The addition of $CeO_2$ nanoparticles lowered the sintering temperature with enhancement in density and grain size as compared to pure MTO ceramics. This is attributed to the higher sintering velocity of the fine particles. Further, the microwave dielectric properties of the MTO ceramics were measured at cryogenic temperatures in the temperature range of 6.5-295 K. It is observed that the loss tangent ($tan{\delta}$) of all the samples increased with temperature. However, the $CeO_2$ nanoparticles doped MTO ceramics manifested lower loss tangents as compared to the pure MTO ceramics. The loss tangents of the pure and MTO ceramics doped with 1.5 wt% of $CeO_2$ nanoparticles measured at 6.5K are found to be $6.6{\times}10^{-5}$ and $5.4{\times}10^{-5}$, respectively. The addition of $CeO_2$ nanoparticles did not cause any changes on the temperature stability of the MTO ceramics at cryogenic temperatures. On the other hand, the temperature coefficient of the permittivity increased with rise in temperature and with the wt% of $CeO_2$ nanoparticles. The obtained lower loss tangent values at cryogenic temperatures can be attributed to the decrease in both intrinsic and extrinsic losses in the MTO ceramics.

• Journal of the Korean Ceramic Society
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• v.29 no.6
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• pp.451-458
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• 1992

Dense glass-ceramics for low firing temperature substrate were prepared by addition of CeO2 flux to the glass of MgO-Al2O3-SiO2 system. Glass powders were fabricated by melting at 150$0^{\circ}C$ and ball milling. Glass powder compacts were sintered at 800~100$0^{\circ}C$ for 3h. The crystallization and the shrinkage behaviors of glass powder compacts were analyzed by XRD, DTA and TMA. The shrinkage of glass powder compact increased with increasing the amount of CeO2. Because the softening temperature decreased and the crystallization temperature increased with increasing the amount of CeO2. Apparently, addition of CeO2 prevented formation of $\mu$-cordierite phase from the glass-ceramics and improved formation of $\alpha$-cordierite phase. Therefore crystallization properties were enhanced.

• Journal of the Korean Ceramic Society
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• v.53 no.4
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• pp.463-467
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• 2016

$Si^{4+}-N^{3-}$ was incorporated into $Ce^{3+}-doped$ lutetium aluminum garnet ($Lu_{2.965}Ce_{0.035}Al_5O_{12}$, $LuAG:Ce^{3+}$) lattices, resulting in the formation of $Lu_{2.965}Ce_{0.035}Al_{5-x}Si_xO_{12-x}N_x$ [(Lu,Ce)AG:xSN]. For x = 0-0.25, the synthesized powders consisted of the LuAG single phase, and the lattice constant decreased owing to the smaller $Si^{4+}$ ions. However, for x > 0.25, a small amount of unknown impurity phases was observed, and the lattice constant increased. Under 450 nm excitation, the PL spectrum of $LuAG:Ce^{3+}$ exhibited the green band, peaking at 505 nm. The incorporation of $Si^{4+}-N^{3-}$ into the $Al^{3+}-O^{2-}$ sites of $LuAG:Ce^{3+}$ led to a red-shift of the emission peak wavelength from 505 to 570 nm with increasing x. Corresponding CIE chromaticity coordinates varied from the green to yellow regions. These behaviors were discussed based on the modification of the $5d^1$ split levels and crystal field surroundings of $Ce^{3+}$, which arose from the Ce-(O,N)8 bonds.

• Korean Chemical Engineering Research
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• v.45 no.6
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• pp.663-668
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• 2007

The autothermal reforming reaction of methane was investigated to produce hydrogen with $Ni/CeO_2-ZrO_2$ catalysts. Alumina-coated honeycomb monolith was applied in order to obtain high catalytic activity and stability in autothermal reforming of methane. Metallic monolithic catalyst showed better methane conversion than that of powder type at high reaction temperature. It was confirmed that $H_2O/CH_4/O_2$ ratio was important factor in autothermal reforming reaction. $H_2$ yield was increased as $H_2O/CH_4$ ratio increased. Methane conversion was improved as $O_2/CH_4$ ratio was increased, whereas, the yield of $H_2$ was decreased. The catalytic activity for $Ni/CeO_2-ZrO_2$ catalyst with 0.5 wt% Ru loading was improved at low reaction temperature.

• Journal of Sensor Science and Technology
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• v.8 no.2
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• pp.195-201
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• 1999

C-axis oriented $YBa_2Cu_3O_{7-{\delta}}$ (YBCO) thin films were grown on $Al_2O_3$ (alumina and R-plane sapphire) substrates by a pulsed laser deposition method. The crystallinity of the $CeO_2$ buffer layer on sapphire substrate exhibit a strong dependence on the deposition temperature, resulting in the growth of a-axis orientation at $800^{\circ}C$. The superconducting properties of YBCO thin films on $Al_2O_3$ substrates showed strong dependence on both thickness and crystallinity of the $CeO_2$ buffer layer. Critical temperature of YBCO film on alumina substrate was ${\sim}83\;K$. In the case of R-plane sapphire substrate,

• Journal of the Korean Ceramic Society
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• v.39 no.3
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• pp.240-244
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• 2002

The GdOBr:Ce phosphor were prepared by solid state reaction using starting chemicals of $Gd_2O_3,\;CeO_2\;and\;NH_4Br$. Under 370nm UV excitation, GdOBr:Ce phosphors showed blue emission band with a spectral range of 410∼430nm. The maximum photoluminescence(PL) emission intensity was observed at 2mol% Ce content. In order to look for feasibility of application for low voltage filed emission display, cathodoluminescence(CL) of GdOBr:Ce phosphors were measured. CL emission spectra was found to be in the range of 410∼430nm, which is the same as PL spectra. The phosphors with 1mol% Ce concentration showed the maximum CL emission intensity. For the comparison of degradation property of the prepared phosphors with commercial ones, the electron beam was applied for 10min. From the result, GdOBr:Ce could be used as a blue phosphor for FED.