• 한국세라믹학회지
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• 제49권1호
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• pp.29-36
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• 2012

In many applications of functional oxides originally homogeneous materials are exposed to gradients in the chemical potential of oxygen. Prominent examples are solid oxide fuel cells (SOFCs) or oxygen permeation membranes (OPMs). Other thermodynamic potential gradients are gradients of electrical potential, temperature or uni-axial pressure. The applied gradients act as generalized thermodynamic forces and induce directed fluxes of the mobile components. These fluxes may lead to three basic degradation phenomena of the materials, which are kinetic demixing, kinetic decomposition, and morphological instabilities.

• The Korean Journal of Ceramics
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• 제4권2호
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• pp.72-77
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• 1998

A defect model for UO$_2$ fuel containing soluble fission products was devised based on the defect structure of pure and doped uranias. Using the equilibrium between fuel solid-solution and fission-products and the material balance within the fuel, a tracing method to get the stoichiometry change of urania fuel with burnup was made. This tracing method was applied to high burnup urania fuel and DUPIC fuel. The oxygen potential of urania fuel turned out to increase slightly with burnup. The stoichiometry change was calculated to be negligible due to the buffering role f Mo. The oxygen potential of DUPIC fuel out to be sensitive to the initial chemical state of Mo in the fuel.

• Nuclear Engineering and Technology
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• 제23권3호
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• pp.321-327
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• 1991

가돌리니아 첨가 우라니아에 대한 점결함 모델이 순수 우라니아의 점결함구조를 바탕으로 하여 개발되었다. Gd 도펀트는 금속이온자리에 -1 유효전하를 지니고, 주위의 산소침입형을 밀어내어 산소침입형의 자리를 감소시킨다. 산소 공공 농도가 증가하면 Gd 도펀트는 산소공공과 집합체를 형성하게 된다. 이 점결함 모델은 Gd 도펀트의 양의 증가에 따른 산소포텐샬의 증가와 산소 대금추비율이 2일때 급속한 산소포텐샬 변화를 설명하여, 현존하는 실험값과 좋은 일치를 보였다.

• The Korean Journal of Ceramics
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• 제6권2호
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• pp.177-182
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• 2000

At the porous $La_{0.6}Ca_{0.4}MnO_{3-{\delta}}$(LCM)/YSZ electrodes of solid oxide fuel cells (SOFC), the electrochemical redox reaction of oxygen proceeds via the triple boundary (TPB) of gas/LCM/YSZ. The surface diffusion of adsorbed oxygen on LCM has been proposed as the rate determining process, assuming the gradient of oxygen chemical potential from the outer surface of porous layer to TPB. Along with the formation of this gradient, oxygen nonstoichiometry in the bulk of LCM may varies. In this paper, an electrochemical technique was described precisely to determine the variation of oxygen content in LCM of porous LCM/YSZ under polarization. It was shown that the oxygen potential in LCM layer under large cathodic polarization is much lower than that in the gas phase, being determined from the electrode potential and Nernst equation.

• 조명전기설비학회논문지
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• 제19권4호
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• pp.79-84
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• 2005

본 논문은 액중 이온교환수 발생장치 내에 양${\cdot}$음이온교환격막을 중심으로 불평등전계를 형성할 수 있는 사선빗살형 전극을 설치하였다. 그리고 정극성과 부극성의 펄스전압을 인가하여 펄스전압의 극성변화에 의한 산화환원전위 변화가 이온교환수 발생장치 내에서 발생된 용존산소량에 미치는 영향을 비교 검토하였다. 실험결과, 이온교환수 발생장치 내에 인가된 펄스전압의 극성변화와 전기비저항의 차에 의한 산화환원전위 및 용존산소농도 변화를 관찰할 수 있었다. 그리고 인가된 펄스전압의 극성변화와 전기 비저항 차에 의한 전위변화가 용존산소농도를 증가시켜 액중에서 고농도의 이온들을 생성시킴을 알 수 있었다.

• Bulletin of the Korean Chemical Society
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• 제17권1호
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• pp.7-11
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• 1996

The interconversion barriers between two twisted conformers of four oxygen-containing cyclohexene analogues have been investigated utilizing a periodic hindered pseudorotational model, molecular mechanics (MM3) calculations, and previously reported far-infrared spectra. The six-fold pseudorotational potential energy function satisfactorily fits the observed bending transitions. The interconversion barrier heights calculated from the pseudorotational model show excellent agreement with those determined from two-dimensional potential energy surfaces for the ring-bending and ring-twisting vibrations. The barriers to interconversion range from 3350 $cm^{-1}$ (9.6 kcal/mol) to 3890 $cm^{-1}$ (11.1 kcal/mol) for four oxygen-containing cyclohexene analogues.

• 한국수산과학회지
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• 제24권5호
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• pp.303-314
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• 1991

반폐쇄만이며 하계동안 저층 빈산소수괴(Hypoxic bottom area)가 형성되는 진해만 일대 해역중의 하나인 원문만에서 해양세균의 계절적 분포와 해양세균이 용존산소소모에 미치는 영향을 알기 위하여 하계동안 미소생물의 전자전달계 활성도(Electron transport system activity)로서 잠재적 산소소모량(potential consumption of oxygen)을 구하였다. 해양세균의 계절별 우점종은 추계('89년 10월)에는 Pseudomonas spp., 동계 ('90년 2월)에는 Serratia spp., 춘계('90년 5월)에는 Acinetobacter spp., 하계('90년 8월)에는 Flavobacterium spp.가 우점하였다. 조사기간동안 생균수는 하계('90년 8월)에 표층, 저층, 저질의 평균치가 각각 $2.12\times10^6cells/ml,\;1.34\times10^6cells/ml,\;1.55\times10^7cells/ml$로 높은 분포치를, 동계에는 표층, 저층, 저질의 평균치가 각각 $2.08\times10^5cells/ml,\;1.54\times10^5cells/ml,\;1.28\times10^6cells/ml$로 낮은 분포치를 보여주었다. 또한 전자전달계 활성(Electron Transport System Activity)으로 잠재적 산소소모량을 조사한 결과 하계동안 수괴에서 미소생물군집의 잠재적 산소소모량은 $232.4-637.5{\mu}l/O_2/l/day$, 이중 세균의 잠재적 산소소모량은 $142.6-432.4{\mu}l/O_2/l/day$로서 수괴의 미소생물군집의 잠재적 산소소모량의 약 $55\%$를 차지하여, 하계동안 저층의 산소소모에 큰 영향을 미침을 알 수 있었으며, 세균의 잠재적 산소소모량은 생균수와 밀접한 관계가 있었다.

• 한국표면공학회지
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• 제37권2호
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• pp.110-118
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• 2004

The corrosion of pure titanium (CP- Ti Grade 2) and titanium alloy (Ti6Al4V ELI) were studied under various conditions of simulated body fluids. The static immersion test and the electrochemical test were performed in accordance with ISO 10271 : 2001. For the electrochemical test, the open circuit potential was monitored as a function of time, and the cyclic polarization curve was recorded. The corrosion resistance was evaluated from the values of corrosion potential, passivation current density, breakdown potential, and the shape of hysteresis etc. The effects of alloy type, surface condition, temperature, oxygen, and constituents in the fluids such as acid, chloride were estimated. Both specimens had extremely low dissolution rate in the static immersion test. They showed strong passivation characteristics in the electrochemical test. They maintained negligible current density throughout the wide anodic potential range. The passive layer was not broken up to 2.0 V (vs. SCE). The hysteresis and the shift of passivation potential toward the anodic direction was observed during the reversed scan. The passivation process appeared to be accelerated by oxygen in air or that dissolved in the fluids. The passivation also proceeded without oxygen by the reaction of constituents in the fluids. Acid or chloride in the fluids, specially later weakened the passive layer, and then induced higher passivation current density and less shift of passivation potential in the reversed scan. CP-Ti Grade 2 was more reactive than Ti6Al4V ELI in the fluids containing acid or chloride, but thicker layer produced on its surface provided higher corrosion resistance.

• 한국표면공학회지
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• 제49권6호
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• pp.498-506
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• 2016

Electrochemical measurement using a LSCF6428 electrode was performed to estimate the oxygen potential gradient in the electrode layer and a long time stability test was performed by applied potential to learn the overpotential effect on the LSCF6428 electrode. By fitting the observed impedance spectra, it was obtained that the amount of faradic current decreased with distance from cathode/electrolyte interface. Oxygen potential gradient was estimated to occur within 1 um region from the cathode/electrolyte interface at an oxygen partial pressure of 10-1 bar. The segregation of cation rich phases in the LSCF6428 electrode suggests that kinetic decomposition took place. However, impedance response after applying the potential showed no changes in the electrode compared with before applying potential. The obtained results suggest that segregation of a secondary phase in a LSCF6428 cathode is not related to performance degradation for solid oxide fuel cells (SOFCs).

• Bulletin of the Korean Chemical Society
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• 제20권11호
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• pp.1303-1308
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• 1999

Conducting poly(3,4-ethylenedioxythiophene) (PEDT) films with metalloporphyrins incorporated as the counter ions were prepared by electropolymerization of the monomer in the presence of metal-tetra(sulfonatophenyl) porphyrin anions. Cathodic reduction of oxygen on the resulting conducting polymer films was studied. The overpotential for O2 reduction on electrodes with cobalt-porphyrin complex was significantly smaller in acidic solutions than on gold. In basic solutions, the overpotential at low current densities was close to those on platinum and gold. Polymer electrode with Co-complex yielded higher limiting currents than with Fe-complex, although the Co-complex polymer electrode was a poorer electrocatalyst for O2 reduction in the activation range of potential than the Fe counterpart. From the rotating ring-disk electrode experiments, oxygen reduction was shown to proceed through either a 4-electron pathway or a 2-electron pathway. In contrast to the polypyr-role-based electrodes, the PEDT-based metalloporphyrin electrodes were stable with wider potential windows, including the oxygen reduction potential. Their electrocatalytic properties were maintained at temperatures up to 80℃ in KOH solutions.