• Corrosion Science and Technology
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• v.11 no.4
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• pp.141-150
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• 2012

Stress corrosion cracks in Alloy 600 compact tension specimens tested at $325^{\circ}C$ in a simulated primary water environment of pressurized water reactor were analyzed by analytical transmission electron microscopy and secondary ion mass spectroscopy (SIMS). From a fine-probe chemical analysis, oxygen was found on the grain boundary just ahead of the crack tip, and chromium oxides were precipitated on the crack tip and the grain boundary attacked by the oxygen diffusion, leaving a Cr/Fe depletion (or Ni enrichment) zone. The oxide layer inside the crack was revealed to consist of a double (inner and outer) layer. Chromium oxides existed in the inner layer, with NiO and (Ni,Cr) spinels in the outer layer. From the nano-SIMS analysis, oxygen was detected at the locations of intergranular chromium carbides ahead of the crack tip, which means that oxygen diffused into the grain boundary and oxidized the surfaces of the chromium carbides. The intergranular chromium carbide blunted the crack tip, thereby suppressing the crack propagation.

• Corrosion Science and Technology
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• v.23 no.1
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• pp.33-40
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• 2024

The concentration and diffusion coefficient of oxide ion vacancies in the oxide scale formed on Fe-22Cr-0.5Mn ferritic stainless steel with and without molybdenum (Mo) was measured at 800℃ by the electrochemical polarization method. After pre-oxidation for 100 h in ambient air at 800 ℃, the oxide scale on one side was completely removed with sandpaper. A YSZ plate was placed on the side where the oxide scale remained. Platinum (Pt) meshes were attached on the top of the YSZ plate and the side where the oxide scale was removed. Changes in electrical current were measured after applying an electrical potential through Pt wires welded to the Pt meshes. The results were interpreted by solving the diffusion equation. The diffusion coefficient and concentration of oxide ion vacancy decreased by 30% and 70% in the specimen with Mo, respectively, compared to the specimen without Mo. The oxide ion vacancy concentration of chromia decreased due to the addition of Mo.

• Fire Science and Engineering
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• v.22 no.5
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• pp.43-47
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• 2008

Recently SIMS has attracted interest as new technique to distinguish the primary and the secondary arc beads. A Cs+ primary ion beam was used to detect the $^{12}C^-$, $^{63}Cu^-$, $^{18}O^-$, $^{35}Cl^-$ secondary ions which are formed during depth profiles in the copper wires. In this work, we studied thermal diffusion in the copper wire which are occurred with supplying over-current. The results demonstrated that Carbon and Chloride are diffused in PVC-coated copper wire deeper than none PVC-coated. However Oxygen showed the reverse diffusion property.

• Journal of the Korean Chemical Society
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• v.15 no.6
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• pp.347-352
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• 1971

The variations of the positive and negative electrode potentials, and of internal pressure were measured during the charge of the sealed type Ni-Cd cell. Both polarization characteristics of a paste type Cd-electrode as a gas diffusion electrode in 30% KOH solution and the effects of active carbon electrode as an oxygen consuming auxiliary electrode of the Ni-Cd cell on the charging characteristics of the cell were studied. Peak voltage at the end of charge of the cell is ascribed to the peak at the negative electrode potential, which is due to the concentration polarization by the lack of $Cd^{++}$ ion and oxygen concentration. And the recovery of the negative electrode potential is resulted from depolarization by the increasing diffusion limiting current density with the increasing oxygen pressure. The active carbon electrode was effective as an oxygen consuming auxiliary electrode. The internal pressure of the cell could be maintained below 200mmHg even at one hour rate charge and overcharge by the use of active carbon electrode as an auxiliary electrode.

• Journal of the Korean Ceramic Society
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• v.38 no.8
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• pp.698-704
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• 2001

Doped ceria의 전기전도도는 도핑 원소의 종류와 양에 큰 의존성을 가지고 특정 조성에서 최대 전도도 값을 가지며 높은 dopant 농도에서는 전기전도도는 감소한다. 이런 현상은 dopant와 산소 빈자리 사이의 회합 형성과 관련이 있다고 알려져 있다. 그러나 Gd 이온이 도핑된 ceria의 경우 주된 회합종이 (2G $d_{Ce}$ $V_{o}$ )인지 (G $e_{Ce}$ $V_{o}$ ) 인지는 명확하게 알려져 있지 않다. 본 연구에서는 회합분포가 전기전도도에 미치는 영향을 연구하기 위해 결함의 회합종과 분포가 다른 3가지 경우에 대해서 시뮬레이션을 행하였다. 분자동력학법을 이용하여 다양한 온도와 다른 회합분포의 경우에 대해 산소 확산계수가 계산되어졌으며, 계산된 산소 확산계수는 실험적으로 결정된 bulk 전도도로부터 얻어진 산소 확산계수와 비교되어졌다. 그 결과 (2G $d_{Ce}$ $V_{o}$ )와 (G $e_{Ce}$ $V_{o}$ ) 회합이 공존하며 이들이 통계학적으로 이항 분포를 가지는 경우가 실험적으로 보고된 값과 가장 일치하는 결과를 얻을 수 있었다.

• Journal of Electrochemical Science and Technology
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• v.3 no.4
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• pp.165-171
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• 2012

An experimental study of mass transfer to an amalgamated copper rotating disc electrode has been employed to determine an empirical correlation for the mass transfer rate in laminar flow. The study was performed in a three-electrodes configuration using 0.1 M boric acid and 0.1M potassium chloride as supporting electrolyte with Zn (II) concentration in the range (25-100 mg $dm^{-3}$). Polarization curves at different zinc ion concentration are reported. Hydrogen and oxygen reduction has also been considered.The diffusion coefficients and mass transfer coefficient were obtained using limiting diffusion current technique based on zinc ion reduction. A least squares analysis indicates that the laminar flow results for 13067 < Re > 57552 and 550 < Sc > 1390 can be correlated by the following equation with correlation coefficient (CR) equal to 0.98: $sh=0.61Re^{0.5}Sc^{1/3}$.

• The Korean Journal of Ceramics
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• v.4 no.2
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• pp.146-150
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• 1998

The total conductivity and oxygen permeation in (Ce1-xZrxO2)0.9(CaO)0.1 solid solutions were measure das a function of temperature and oxygen partial pressure. Empirically, σ at given x and T was expressed essentially by σ=σo2+σeo Po2-1/4, where σo2 and σeo are constant. Applying a standard defect model in which major defects are Cace", Cece' and Vo in ideal solution, we can assign σo2 as the oxide ion conductivity decreases while the electronic conductivity increases with the increase in Zr content. Using the oxide ion and electronic conductivities thus determined, the oxygen permeation flux was calculated for respective Po2 and T conditions at which the measurements were made. The calculated values were found to agree with the observed ones.

• Journal of the Korean Vacuum Society
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• v.5 no.1
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• pp.39-47
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• 1996

The segregation of S in electrotransport-purified polycrystaline $\alpha$-Ti and Ti-aluminide alloys has been studied by Auger electron spectroscopy(AES), Ion scattering spectroscopy(ISS) and Secondary ion mass spectrometry(SIMS) in the temperature range extending from 20 to $1000^{\circ}C$. The chemisorbed oxygen and carbon on Ti were observed to disappear at T>$400^{\circ}C$ after which the S signal increased to levels approaching 0.5 monolayer. At lower temperatures the presence of the surface oxygen and carbon appeared to inhibit the segregation, presumably because there were no available surfaces sites for the S emerging from the bulk. The activation energy for the S segregation in pure polycrystaline Ti was determined to be 16.7 kcal/mol, which, when compared to S segretation from single-crystal Ti, is quite small and suggests grain boundary or defect diffusion segregation kinetics. In the Ti-aluminide alloys, the presence of Al appeared to enhance the retention of surface oxygen which, in turn, substantially reduced the S segretation. The $\gamma$ alloy, with its high Al content, exhibited the greatest retention of surface oxygen and the smallest quantity of the S segregation(T$\simeq1000^{\circ}C$).

• Journal of the Korea Safety Management & Science
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• v.20 no.4
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• pp.7-13
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• 2018

This study investigates the enhancement of the oxygen diffusion rate in the cathode channel of a proton exchange membrane fuel cell (PEMFC) by pure oscillating flow, which is the same as the mechanism of human breathe. Three-dimensional numerical simulation, which has the full model of the fuel cell including electrochemical reaction, ion and electronic conduction, mass transfer and thermal variation and so on, is performed to show the phenomena in the channel at the case of a steady state. This model could analysis the oscillating flow as a moving mesh calculation coupled with electrochemical reaction on the catalyst layer, however, it needs a lot of calculation time for each case. The two dimensional numerical simulation has carried on for the study of oscillating flow effect in the cathode channel of PEMFC in order to reduce the calculation time. This study shows the diffusion rate of the oxygen increased and the emission rate of the water vapor increased in the channel by oscillating flow without any forced flow.

• Journal of the Semiconductor & Display Technology
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• v.20 no.1
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• pp.54-58
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• 2021

The RGO with controllable oxygen functional groups is a novel material as the active layer of resistive switching memory through a reduction process. We designed a nanoscale conductive channel induced by local oxygen ion diffusion in an Au / RGO+GQD / Al resistive switching memory structure. A strong electric field was locally generated around the Al metal channel generated in BIL, and the local formation of a direct conductive low-dimensional channel in the complex RGO graphene quantum dot region was confirmed. The resistive memory design of the complex RGO graphene quantum dot structure can be applied as an effective structure for charge transport, and it has been shown that the resistive switching mechanism based on the movement of oxygen and metal ions is a fundamental alternative to understanding and application of next-generation intelligent semiconductor systems.