• Journal of the Korean Chemical Society
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• v.37 no.4
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• pp.390-395
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• 1993

The x values and electrical conductivities of the nonstoichiometric compounds$ CeO_{2-x} have been measured in a temperature range from 600 to 1200$^{\circ}C$ under oxygen partial pressure of $2{\times}10^{-1}{\sim}1{\times}10^{-4}$ atm. The enthalpy of the defect formation shows an endothermic process with the oxygen partial pressure dependence (1/n value) of -1/3.18 ∼ -1/3.69. The activation energy and 1/n value for the electrical conductivity are estimated as 1.75 eV and -1/4, respectively. According to the x values, the $\sigma$ values, and the thermodynamic data, the defect structure of the ceria seems to be the formation of singly charged negative oxygen vacancies. The n-type semiconducting behaviors could be explained by the presence of excess metals in the lattice as the conduction electron donor.

• Membrane Journal
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• v.15 no.3
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• pp.198-205
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• 2005

Double-layered polymer films to assay the radioactive contamination were formulated using polysulfone (PSF) and cerium activated yttrium silicate (CAYS), consisting of a dense support layer and a CAYS-holding top layer prepared via the diffusion-induced phase inversion. As the vapor exposure process was omitted, the CAYS-holding layer showed a typical asymmetric structure, with CAYS being transfixed into the polymer network spread with large macropores. With the increase in vapor exposure time before immersion, morphology of the films transformed from asymmetric to sponge-like structures, with CAYS being localized in cellular structure. The border structure between the two layers reflects the phase inversion behavior of a cast solution during the coagulation. In the radioactive detection, the polymer phase in a film holding a sponge-like structure is so dense that the radionuclides, deposited on the film, could not filter through the phase, consequently resulting in the loss in the detection efficiency of the film.

• Transactions of the Korean hydrogen and new energy society
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• v.23 no.5
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• pp.437-447
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• 2012

Ceria ($CeO_2$) was used to scavenge free radicals which attack the membrane in the polymer electrolyte membrane water electrolysis (PEMWE) circumstance and to increase the duration of the membrane. In order to improve the electrochemical, mechanical and electrocatalytic characteristics, engineering plastic of the sulfonated polyether ether ketone (SPEEK) as polymer matrix was prepared in the sulfonation reaction of polyether ether ketone (PEEK) and the organic-inorganic blended composite membranes were prepared by sol-gel casting method with loading the highly dispersed ceria and cesium-substituted tungstophosphoric acid (Cs-TPA) with cross-linking agent contents of 0.01 mL. In conclusion, CL-SPEEK/Cs-TPA/ceria (1%) membrane showed the optimum results such as 0.130 S/cm of proton conductivity at $80^{\circ}C$, 2.324 meq./g-dry-membrane of ion exchange capacity and mechanical characteristics, and 65.03 MPa of tensile strength which were better than Nafion 117 membrane.

• Bulletin of the Korean Chemical Society
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• v.19 no.6
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• pp.671-676
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• 1998

The formation and dissociation rates of $Ce^{3+}$ Complexes of the 1,4,7,10-tetraaza-13,16-dioxacyclooctadecane-NN', N",N"'-tetraacetic acid (1), 1,4,7,10-tetraaza-13,16-dioxacyclooctadecane-N,N',N",N"'-tetramethylacetic acid (2), and 1,4,7,10-tetraaza-13,16-dioxacyclooctadecane-N,N',N",N"'-tetrapropionic acid (3) have been measured by the use of stopped-flow spectrophotometry. Observations were made at 25.0±0.1 ℃ and at an ionic strength of 0.10 M $NaClO_4$. The complexation of $Ce^{3+}$ ion with 1 and 2 proceeds through the formation of an intermediate complex $(CeH_3L^{2+})^*$ in which the $Ce^{3+}$ ion is incompletely coordinated. This may then lead to be a final product in the rate-determining step. Between pH 4.76 and 5.76, the diprotonated $(H_2L^{2-})$ from is revealed to be a kinetically active species despite of its low concentration. The stability constants $(logK(CeH_3L^{2+}))$ and specific water-assisted rate constants $(k_{OH})$ of intermediate complexes have been determined from the kinetic data. The dissociation reactions of $Ce^{3+}$ complexes of 1, 2, and 3 were investigated with $Cu^{2+}$, ions as a scavenger in acetate buffer. All complexes exhibit acid-independent and acid-catalyzed contributions. The effect of buffer and $Cu^{2+}$ concentration on the dissociation rate has also been investigated. The ligand effect on the dissociation rate of $Ce^{3+}$ complexes is discussed in terms of the side-pendant arms and the chelate ring sizes of the ligands.

• Journal of Radiation Protection and Research
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• v.47 no.4
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• pp.214-225
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• 2022

Background: The conventional cerium-doped Gd₂Al₂Ga₃O₁₂ (GAGG(Ce)) scintillator-based gamma-ray imager has a bulky detector, which can lead to incorrect positioning of the gammaray source if the shielding against background radiation is not appropriately designed. In addition, portability is important in complex environments such as inside nuclear power plants, yet existing gamma-ray imager based on a tungsten mask tends to be weighty and therefore difficult to handle. Motivated by the need to develop a system that is not sensitive to background radiation and is portable, we changed the material of the scintillator and the coded aperture. Materials and Methods: The existing GAGG(Ce) was replaced with Bi₄Ge₃O₁₂ (BGO), a scintillator with high gamma-ray detection efficiency but low energy resolution, and replaced the tungsten (W) used in the existing coded aperture with lead (Pb). Each BGO scintillator is pixelated with 144 elements (12 × 12), and each pixel has an area of 4 mm × 4 mm and the scintillator thickness ranges from 5 to 20 mm (5, 10, and 20 mm). A coded aperture consisting of Pb with a thickness of 20 mm was applied to the BGO scintillators of all thicknesses. Results and Discussion: Spectroscopic characterization, imaging performance, and image quality evaluation revealed the 10 mm-thick BGO scintillators enabled the portable gamma-ray imager to deliver optimal performance. Although its performance is slightly inferior to that of existing GAGG(Ce)-based gamma-ray imager, the results confirmed that the manufacturing cost and the system's overall weight can be reduced. Conclusion: Despite the spectral characteristics, imaging system performance, and image quality is slightly lower than that of GAGG(Ce), the results show that BGO scintillators are preferable for gamma-ray imaging systems in terms of cost and ease of deployment, and the proposed design is well worth applying to systems intended for use in areas that do not require high precision.

• Clean Technology
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• v.29 no.4
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• pp.321-326
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• 2023

Recently, there has been a growing interest in clean hydrogen energy that does not emit carbon dioxide during combustion due to the increasing focus on carbon neutral. Research related to hydrogen production continues, and in this study, we applied waste-derived synthesis gas to the water-gas shift reaction to simultaneously treat waste and produce high-purity hydrogen. To enhance catalytic activity in the high-temperature water-gas shift (HT-WGS) reaction, magnesium was used as a support material alongside cerium. Cu-CeO₂-MgO catalysts were synthesized, with copper acting as the active component for the HT-WGS reaction. A study on the catalytic activity based on the preparation method was conducted, and the Cu-CeO₂-MgO catalyst prepared by impregnation method exhibited the highest activity in the HT-WGS reaction. The observed superior performance of the Cu-CeO₂-MgO catalyst prepared through the impregnation method can be attributed to its significantly higher oxygen storage capacity and amount of active Cu species.

• Journal of Chest Surgery
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• v.35 no.5
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• pp.343-349
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• 2002

background: In an attempt to investigate the role of oxidants in the activation of phospholipase $A_2$(PLA$_2$) and endogenous oxidative stress in the lung. acute inflammatory lung injury was induced by the instillation of hydrogen peroxide into the trachea of Sprague-Dawley rats. Material and Method: To prove the hypothesis thats released oxidants from neutrophils activate the PLA$_2$ retrogradely, activities of PLA$_2$ and lysoplatelet activating factor acetyltransferase(lysoPAF AT) were assayed i hours after instillation of hydrogen peroxide. In addition, to confirm the impairing effects of the activation of PLA$_2$ associated with endogenous oxidative stress, lung weight/body weight ratio(L$\times$10$^{-3}$ B), protein contents(mg/two lungs) in bronchoalveolar lavage(BAL) were measured. As neutrophilic respiratory burst has been known to play a pivotal role in the genesis of endogenous oxidative stress associated with acute inflammatory lung injury, BAL neutrophils counts and level of lung myelperoxidase(MPO) were measured after hydorgen peroxide insult. Morphological and histochemical studies were also performed to identify the effect of the endogenous oxidative stress. Result: Five hours after hydrogen peroxide instillation, lungs showed marked infiltration of neutrophils and increased weight. Protein contents in BAL increased significantly compared to those of normal rats. PLA$_2$ activity was enhanced in the hydrogen peroxide instilled group. Interestingly, the accelerated production of platelet activating factor(PAF) was confirmed by the increased activity of lysoPAF AT in the $H_2O$$_2$ employed lung. Morphologically, light microscopic findings of lungs after instillation of hydrogen peroxide showed atelectasis and infiltration of inflammatory cells, which was thought to be caused by lipid mediators produced by PLA$_2$ activation. In cerium chloride cytochemical electron microscopy, dense deposits of cerrous perhydroxide were identified. In contrast, no deposit of cerrous perhydroxide was found in the normal lung.

• Journal of the Korean Electrochemical Society
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• v.1 no.1
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• pp.1-7
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• 1998

For the purpose of finding new cathode materials for medium-temperature $(700\~800^{\circ}C)$ solid oxide fuel cells, $Gd_{0.8}Ca_{0.2}Co_{1-x}Fe_xO_3,\;(x=0.0\~0.5)$ are prepared, and their thermal stability and conductivity characteristics are investigated. Also, the cathodic activities are measured after the cathode layer being attached on CGO (cerium-gadolinium oxide) electrolyte disk. The X-ray analyses indicate that the materials prepared by calcining the citrate-gels at $800^{\circ}C$ have the orthorhombic perovskite structure without discernible impurities. The thermal stability of the undoped Co perovskite is so poor that it is decomposed to the individual binary oxide even at $1300^{\circ}C$. But the partially Fe-doped cobaltates exhibit a better thermal stability to retain their structural integrity up to $1400^{\circ}C$. The observation whereby both the undoped and Fe-doped cobaltates melt at ca. $1300^{\circ}C$ leads us to perform the electrode adhesion at <$1300^{\circ}C$. The cathodic activity of $Gd_{0.8}Ca_{0.2}Co_{1-x}Fe_xO_3,\;(x=0.0\~0.5)$, electrodes is superior to $La_{0.9}Sr_{0.1}MnO_3$, among the samples of $x=0.0\~0.5$, the x=0.2 cathode shows the best activity for the oxygen reduction reaction. It is likely that the Fe-doping provides a better thermal stability to the materials but in turn imparts an inferior cathodic activity, such that the optimum trade-off is made at x=0.2 between the two factors. The total electrical conductivity and ion conductivity of $Gd_{0.8}Ca_{0.2}Co_{1-x}Fe_xO_3$, are measured to be 51 S/cm and $6.0\times10^{-4}S/cm\;at\;800^{\circ}C$, respectively. The conductivity values illustrate that the materials are a mixed conductor and the reaction sites can be expanded to the overall electrode surface, thereby providing a better cathodic activity than $La_{0.9}Sr_{0.1}MnO_3$.

• Analytical Science and Technology
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• v.5 no.1
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• pp.41-49
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• 1992

An attempt was made to prepare two series of tetrakis eight-coordinate tungsten(IV) and cerium(IV) complexes containing the 5,7-dichloro-8-quinolinol(N:${\pi}$-acceptor atom, O:${\pi}$-donor atom) ligand. Tetrakis eight-coordinate tungsten(IV) complex of 2-mercaptopyrimidine(N:${\pi}$-acceptor atom, S:${\pi}$-donor atom) ligand have also been prepared. And the new series of mixed-ligand eight-coordinate tungsten(IV) complexes containing bidentate ligands 5,7-dichloro-8-quinolinol and 2-mercaptopyrimidine have been prepared, isolated by TLC and characterized. $W(dcq)_4$, $W(dcq)_3(mpd)_1$, $W(dcq)_2(mpd)_2$, $W(dcq)_1W(dcq)_3$ and $W(mpd)_4$ complexes of MLCT absorption band appeared to 710nm, 680nm, 625nm, 581nm, and 571nm(${\varepsilon}\;max={\sim}>{\times}10^4$) on low-energy respectively. The specific absorption wave length of $Ce(dcq)_4$ is appeared 520nm(${\varepsilon}\;max={\sim}>{\times}10^4$). The Chemical shift values by proton of coordinated position appeared to $W(dcq)_4$ [$H_2:8.9ppm$]; $W(dcq)_3(mpd)_1$ [$H_2:9.3$,$H_6:9.2ppm$]; $W(dcq)_2(mpd)_2$ [$H_2:9.7$,$H_6:8.95ppm$]; $W(dcq)_1(mpd)_3$ [$H_2:9.8$,$H_6:9.4ppm$]; $W(mpd)_4$ [$H_6:8.8ppm$]; $Ce(dcq)_4$ [$H_2:9.3ppm$] with $^1H$-NMR. The inertness of mixed-ligand eight coordinate tungsten(IV) complexes have been investigated by UV-Vis. spectroscopic method in dimethylsulfoxide at $90^{\circ}C$. The inertness of $W(dcq)_n(mpd)_{4-n}$ complexes showed the following order, $W(dcq)_3(mpd)_1;k_{obs.}=3.8{\times}10^{-6}$ > $W(mpd)_4;k_{obs.}=6.0{\times}10^{-6}$ > $W(dcq)_4;k_{obs.}=6.4{\times}10^{-6}$ > $W(dcq)_2(mpd)_2;k_{obs.}=7.0{\times}10^{-6}$ > $W(dcq)_1(mpd)_3;k_{obs.}=1.7{\times}10^{-5}$, which showed the inertness until 16days, 10days, 9days, 8days, and 4days. The $W(mpd)_4$ is very inert as $k_{obs.}=3.6{\times}10^{-6}$(16days) in xylene at $90^{\circ}C$ and $k_{obs.}=6.0{\times}10^{-6}$(10days) in DMSO at $90^{\circ}C$.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.185-185
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• 2012

중공 발광 나노 물질은 특유의 구조적 특성(낮은 밀도, 높은 비표면적, 다공성 물질, 낮은 열팽창계수 등)과 광학적 성질을 이용하여 디스플레이 패널, 광결정, 약물전달체, 바이오 이미징 라벨 등의 다양한 적용이 가능하다. 이러한 적용에 있어 균일한 크기와 형태의 중공 입자는 필수 조건으로 여겨진다. 지금까지 합성된 중공 발광 입자에는 BaMgAl10O17 : Eu2+-Nd3+, Gd2O3 : Eu3+, $EuPO_4{\cdot}H_2O$과 같은 것들이 있으나 크기 조절이 어렵고, 그 균일성이 확보되지 못하였다. 균일한 크기의 중공 발광 입자를 만들기 위해 SiO2나 emulsion을 템플릿으로 이용하여 황화카드뮴, 카드뮴 셀레나이드 중공 입자를 합성한 예가 있으나, 양자점의 독성으로 인하여 바이오분야 응용에는 적합하지 않다. YAG는 모체로써 형광체에서 가장 많이 이용되는 물질로, 화학적 안정성과 낮은 독성, 높은 양자 효율 등 많은 장점을 갖고 있다. 특히 세륨이 도핑된 YAG형광체의 경우 WLED, 신틸레이터, 바이오산업에 적용이 가능하다. 그러나 지금까지 중공 YAG:Ce3+형광체를 합성한 예가 없었다. 본 연구에서는 단분산 수화 알루미늄 (Al(OH)3) 입자 위에 세륨이 도핑 된 이트륨 베이직 카보네이트 ($Y(OH)CO_3$)를 균일하게 코팅한 후 열처리를 하여 균일한 크기의 Y3Al5O12:Ce3+(YAG) 중공 입자를 합성하였다. 열처리 온도에 따른 고분해능 투과 전자 현미경(HRTEM), X-선 회절(XRD), 고분해능 에너지 분광법(HREDX) 분석결과, 중공 YAG: Ce3+입자는 Kirkendall 효과에 의해 형성됨을 확인하였다. 전계방사형 주사 전자 현미경(FE-SEM) 측정을 통해, 열처리 후에도 입자의 크기와 형태가 균일함을 확인하였으며, 공초점 현미경 관찰을 통해 중공 형태를 명확히 확인 할 수 있었다. Photoluminescence (PL) 분광법과 형광 수명 이미징 현미경(FLIM)을 이용한 광 특성 분석결과, 합성된 입자는 400-500 nm에서 흡수 파장 (456 nm에서 최대 강도)과 500-700 nm 범위의 발광 파장(544 nm에서 최대 강도)을 나타냈고, 상용 YAG: Ce3+(70 ns)에 준하는 74 ns의 잔광 시간(decay time)이 측정되었다. 단분산 수화 알루미늄 입자의 크기를 조절하여 최종 합성된 YAG: Ce3+의 크기를 조절할 수 있었다. 지름 약 600 nm의 Al(OH)3를 사용한 경우, $1,300^{\circ}C$에서 열처리를 한 후 평균 지름 590 nm의 중공입자를 합성하였고, 약 170 nm의 Al(OH)3를 이용하여, 더 낮은 온도인 $1,100^{\circ}C$에서의 열처리를 통해 평균지름 140 nm의 중공 YAG: Ce3+입자를 합성하였다. 본 연구를 통하여 합성된 균일한 크기의 YAG 중공입자는 LED와 같은 광전변환 소자 및 다기능성 바이오 이미징 등의 나노바이오 소자 분야에 활용될 수 있음이 기대된다.