Reoxidation

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Tatsumi Ishihara - One of the best experts on this subject based on the ideXlab platform.

  • improved Reoxidation tolerance of ni fe metal support for lagao3 thin film electrolyte cell
    Solid State Ionics, 2012
    Co-Authors: Young-wan Ju, Toru Inagaki, Tatsumi Ishihara
    Abstract:

    Abstract Effects of Reoxidation and reduction treatment of a Ni–Fe metallic anode substrate were investigated as a function of Reoxidation period and temperature. The NiFe 2 O 4 composite anode substrate was highly dense before the reduction treatment. However, after reduction for 2 h in H 2 atmosphere, the dense oxide composite substrate was changed to a porous metal substrate consisting of a Ni–Fe alloy. The metallic substrate was then reoxidized in 100% O 2 . When the Reoxidation treatment was performed, the porous substrate regained its original density. However, XRD patterns of the reoxidized substrate still exhibited strong Ni base alloy peaks. Moreover, SEM–EDX analysis showed that a large part of the reoxidized substrate was porous and a dense iron base oxide layer formed at the surface of the substrate. In addition, after reduction for 2 h with hydrogen gas, the substrate returned to a porous metal substrate again. Therefore, in spite of slightly increased anodic IR loss and a small fuel-leakage, which was observed after the Reoxidation and reduction cycles, the Ni–Fe metal supported cell showed an excellent Reoxidation tolerance at 973 K.

  • Improved Reoxidation tolerance of Ni-Fe metal support for LaGaO 3 thin film electrolyte cell
    Solid State Ionics, 2012
    Co-Authors: Young-wan Ju, Toru Inagaki, Shintaro Ida, Tatsumi Ishihara
    Abstract:

    Effects of Reoxidation and reduction treatment of a Ni-Fe metallic anode substrate were investigated as a function of Reoxidation period and temperature. The NiFe 2O 4 composite anode substrate was highly dense before the reduction treatment. However, after reduction for 2 h in H 2 atmosphere, the dense oxide composite substrate was changed to a porous metal substrate consisting of a Ni-Fe alloy. The metallic substrate was then reoxidized in 100% O 2. When the Reoxidation treatment was performed, the porous substrate regained its original density. However, XRD patterns of the reoxidized substrate still exhibited strong Ni base alloy peaks. Moreover, SEM-EDX analysis showed that a large part of the reoxidized substrate was porous and a dense iron base oxide layer formed at the surface of the substrate. In addition, after reduction for 2 h with hydrogen gas, the substrate returned to a porous metal substrate again. Therefore, in spite of slightly increased anodic IR loss and a small fuel-leakage, which was observed after the Reoxidation and reduction cycles, the Ni-Fe metal supported cell showed an excellent Reoxidation tolerance at 973 K. © 2012 Elsevier B.V. All rights reserved.

  • Reoxidation behavior of ni fe bimetallic anode substrate in solid oxide fuel cells using a thin lagao3 based film electrolyte
    Journal of Power Sources, 2011
    Co-Authors: Young-wan Ju, Toru Inagaki, Tatsumi Ishihara
    Abstract:

    Abstract The Reoxidation behavior of a Ni–Fe metal anode supported cell using a thin LaGaO 3 electrolyte film was investigated as a function of the Reoxidation temperature. After oxidation and reduction treatments for 2 h, the voltage did not return to the initial voltage at higher temperatures (773–973 K); however, after Reoxidation at 673 K, the cell exhibited almost the same OCV as the as-prepared cell. During Reoxidation with air at the higher temperatures, the Ni–Fe metal substrate exhibited two different expansion behaviors by the different oxidation rates of Ni and Fe. On the other hand, the volumetric change of the oxidized substrate at 673 K was negligible. SEM-EDX results exhibited the Reoxidation of Ni–Fe occurred only at the bottom part of the substrate and at the interface between the electrolyte and the substrate. In spite of temperatures as low as 673 K, the cell generated a power of 160 mW cm −2 , which hardly decreased after the redox cycle. The increasing anodic internal resistance accompanied with unreduced Fe.

Young-wan Ju - One of the best experts on this subject based on the ideXlab platform.

  • improved Reoxidation tolerance of ni fe metal support for lagao3 thin film electrolyte cell
    Solid State Ionics, 2012
    Co-Authors: Young-wan Ju, Toru Inagaki, Tatsumi Ishihara
    Abstract:

    Abstract Effects of Reoxidation and reduction treatment of a Ni–Fe metallic anode substrate were investigated as a function of Reoxidation period and temperature. The NiFe 2 O 4 composite anode substrate was highly dense before the reduction treatment. However, after reduction for 2 h in H 2 atmosphere, the dense oxide composite substrate was changed to a porous metal substrate consisting of a Ni–Fe alloy. The metallic substrate was then reoxidized in 100% O 2 . When the Reoxidation treatment was performed, the porous substrate regained its original density. However, XRD patterns of the reoxidized substrate still exhibited strong Ni base alloy peaks. Moreover, SEM–EDX analysis showed that a large part of the reoxidized substrate was porous and a dense iron base oxide layer formed at the surface of the substrate. In addition, after reduction for 2 h with hydrogen gas, the substrate returned to a porous metal substrate again. Therefore, in spite of slightly increased anodic IR loss and a small fuel-leakage, which was observed after the Reoxidation and reduction cycles, the Ni–Fe metal supported cell showed an excellent Reoxidation tolerance at 973 K.

  • Improved Reoxidation tolerance of Ni-Fe metal support for LaGaO 3 thin film electrolyte cell
    Solid State Ionics, 2012
    Co-Authors: Young-wan Ju, Toru Inagaki, Shintaro Ida, Tatsumi Ishihara
    Abstract:

    Effects of Reoxidation and reduction treatment of a Ni-Fe metallic anode substrate were investigated as a function of Reoxidation period and temperature. The NiFe 2O 4 composite anode substrate was highly dense before the reduction treatment. However, after reduction for 2 h in H 2 atmosphere, the dense oxide composite substrate was changed to a porous metal substrate consisting of a Ni-Fe alloy. The metallic substrate was then reoxidized in 100% O 2. When the Reoxidation treatment was performed, the porous substrate regained its original density. However, XRD patterns of the reoxidized substrate still exhibited strong Ni base alloy peaks. Moreover, SEM-EDX analysis showed that a large part of the reoxidized substrate was porous and a dense iron base oxide layer formed at the surface of the substrate. In addition, after reduction for 2 h with hydrogen gas, the substrate returned to a porous metal substrate again. Therefore, in spite of slightly increased anodic IR loss and a small fuel-leakage, which was observed after the Reoxidation and reduction cycles, the Ni-Fe metal supported cell showed an excellent Reoxidation tolerance at 973 K. © 2012 Elsevier B.V. All rights reserved.

  • Reoxidation behavior of ni fe bimetallic anode substrate in solid oxide fuel cells using a thin lagao3 based film electrolyte
    Journal of Power Sources, 2011
    Co-Authors: Young-wan Ju, Toru Inagaki, Tatsumi Ishihara
    Abstract:

    Abstract The Reoxidation behavior of a Ni–Fe metal anode supported cell using a thin LaGaO 3 electrolyte film was investigated as a function of the Reoxidation temperature. After oxidation and reduction treatments for 2 h, the voltage did not return to the initial voltage at higher temperatures (773–973 K); however, after Reoxidation at 673 K, the cell exhibited almost the same OCV as the as-prepared cell. During Reoxidation with air at the higher temperatures, the Ni–Fe metal substrate exhibited two different expansion behaviors by the different oxidation rates of Ni and Fe. On the other hand, the volumetric change of the oxidized substrate at 673 K was negligible. SEM-EDX results exhibited the Reoxidation of Ni–Fe occurred only at the bottom part of the substrate and at the interface between the electrolyte and the substrate. In spite of temperatures as low as 673 K, the cell generated a power of 160 mW cm −2 , which hardly decreased after the redox cycle. The increasing anodic internal resistance accompanied with unreduced Fe.

Toru Inagaki - One of the best experts on this subject based on the ideXlab platform.

  • improved Reoxidation tolerance of ni fe metal support for lagao3 thin film electrolyte cell
    Solid State Ionics, 2012
    Co-Authors: Young-wan Ju, Toru Inagaki, Tatsumi Ishihara
    Abstract:

    Abstract Effects of Reoxidation and reduction treatment of a Ni–Fe metallic anode substrate were investigated as a function of Reoxidation period and temperature. The NiFe 2 O 4 composite anode substrate was highly dense before the reduction treatment. However, after reduction for 2 h in H 2 atmosphere, the dense oxide composite substrate was changed to a porous metal substrate consisting of a Ni–Fe alloy. The metallic substrate was then reoxidized in 100% O 2 . When the Reoxidation treatment was performed, the porous substrate regained its original density. However, XRD patterns of the reoxidized substrate still exhibited strong Ni base alloy peaks. Moreover, SEM–EDX analysis showed that a large part of the reoxidized substrate was porous and a dense iron base oxide layer formed at the surface of the substrate. In addition, after reduction for 2 h with hydrogen gas, the substrate returned to a porous metal substrate again. Therefore, in spite of slightly increased anodic IR loss and a small fuel-leakage, which was observed after the Reoxidation and reduction cycles, the Ni–Fe metal supported cell showed an excellent Reoxidation tolerance at 973 K.

  • Improved Reoxidation tolerance of Ni-Fe metal support for LaGaO 3 thin film electrolyte cell
    Solid State Ionics, 2012
    Co-Authors: Young-wan Ju, Toru Inagaki, Shintaro Ida, Tatsumi Ishihara
    Abstract:

    Effects of Reoxidation and reduction treatment of a Ni-Fe metallic anode substrate were investigated as a function of Reoxidation period and temperature. The NiFe 2O 4 composite anode substrate was highly dense before the reduction treatment. However, after reduction for 2 h in H 2 atmosphere, the dense oxide composite substrate was changed to a porous metal substrate consisting of a Ni-Fe alloy. The metallic substrate was then reoxidized in 100% O 2. When the Reoxidation treatment was performed, the porous substrate regained its original density. However, XRD patterns of the reoxidized substrate still exhibited strong Ni base alloy peaks. Moreover, SEM-EDX analysis showed that a large part of the reoxidized substrate was porous and a dense iron base oxide layer formed at the surface of the substrate. In addition, after reduction for 2 h with hydrogen gas, the substrate returned to a porous metal substrate again. Therefore, in spite of slightly increased anodic IR loss and a small fuel-leakage, which was observed after the Reoxidation and reduction cycles, the Ni-Fe metal supported cell showed an excellent Reoxidation tolerance at 973 K. © 2012 Elsevier B.V. All rights reserved.

  • Reoxidation behavior of ni fe bimetallic anode substrate in solid oxide fuel cells using a thin lagao3 based film electrolyte
    Journal of Power Sources, 2011
    Co-Authors: Young-wan Ju, Toru Inagaki, Tatsumi Ishihara
    Abstract:

    Abstract The Reoxidation behavior of a Ni–Fe metal anode supported cell using a thin LaGaO 3 electrolyte film was investigated as a function of the Reoxidation temperature. After oxidation and reduction treatments for 2 h, the voltage did not return to the initial voltage at higher temperatures (773–973 K); however, after Reoxidation at 673 K, the cell exhibited almost the same OCV as the as-prepared cell. During Reoxidation with air at the higher temperatures, the Ni–Fe metal substrate exhibited two different expansion behaviors by the different oxidation rates of Ni and Fe. On the other hand, the volumetric change of the oxidized substrate at 673 K was negligible. SEM-EDX results exhibited the Reoxidation of Ni–Fe occurred only at the bottom part of the substrate and at the interface between the electrolyte and the substrate. In spite of temperatures as low as 673 K, the cell generated a power of 160 mW cm −2 , which hardly decreased after the redox cycle. The increasing anodic internal resistance accompanied with unreduced Fe.

Peter Storkholm - One of the best experts on this subject based on the ideXlab platform.

  • sulphate reduction and sulphur cycling in lake sediments a review
    Freshwater Biology, 2001
    Co-Authors: Marianne Holmer, Peter Storkholm
    Abstract:

    1. The concentration of sulphate is low in lakes and sulphur cycling has often been neglected in studies of organic matter diagenesis in lake sediments. The cycling of sulphur is, however, both spatially and temporally dynamic and strongly influences many biogeochemical reactions in sediments, such as the binding of phosphorus. This review examines the control of sulphate reduction and sulphur cycling in sediments of lakes with different trophic status. 2. The factors that control the rate of sulphate reduction have not been identified with certainty in the various environments because many factors are involved, e.g. oxygen and sulphate concentrations, temperature and organic matter availability. 3. Sulphate reduction is less significant under oligotrophic conditions, where mineralization is dominated by oxic decomposition. The supply of organic matter may not be sufficient to support sulphate reduction in the anoxic parts of sediments and, also, sulphate availability may control the rate as the concentration is generally low in oligotrophic lakes. 4. There is a potential for significant sulphate reduction in eutrophic lakes, as both the availability of organic matter and sulphate concentration are often higher than in oligotrophic lakes. Sulphate is rapidly depleted with sediment depth, however, and methanogenesis is generally the most important process in overall carbon mineralization. Sulphate reduction is generally low in acidic lakes because of low sulphate availability and reduced microbial activity. 5. It is still unclear which of the forms of sulphur deposits are the most important and under which conditions burial occurs. Sulphur deposition is controlled by the rate of sulphate reduction and Reoxidation. Reoxidation of sulphides occurs rapidly through several pathways, both under oxic and anoxic conditions. Only a few studies have been able to examine the importance of Reoxidation, but it is hypothesized that most of the Reoxidation takes place under anoxic conditions and that disproportionation is often involved. The presence of sulphide oxidizing bacteria, benthic fauna and rooted macrophytes may substantially enhance oxic Reoxidation. Deposition of sulphur is generally higher in eutrophic than in oligotrophic lakes because of a number of factors: a higher rate of sulphate reduction, enhanced sedimentation of organic sulphur and less Reoxidation as a result of reduced penetration of oxygen into the sediments, a lack of faunal activity and rooted macrophytes.

F Cosandey - One of the best experts on this subject based on the ideXlab platform.

  • low temperature Reoxidation mechanism in nanocrystalline tio2 δ thin films
    Journal of The Electrochemical Society, 2001
    Co-Authors: Avner Rothschild, Y Komem, F Cosandey
    Abstract:

    This paper deals with the Reoxidation of nanocrystalline TiO 2 δ thin films during exposure to ambient oxygen at relatively low temperatures. A phenomenological model is proposed to describe the Reoxidation mechanism and its influence on the electrical conductance's sensitivity to oxygen, taking into account both surface and bulk processes. Chemisorption of oxygen predominates during the lirst few minutes, followed by diffusion of oxygen into the film and recombination with oxygen vacancies. The model describes the kinetics of the change in the electrical conductance during the transition from the initial to the final equilibrium states. Logarithmic and modified parabolic laws are derived to describe the change in the conductance as a function of time during the first (surface-controlled) and second (bulk-controlled) stages of the Reoxidation reaction, respectively. It is demonstrated that these expressions fit very well with experimental results from nanocrystalline TiO 2 δ thin films during exposure to ambien oxygen at constant temperatures between 200 and 325°C.

  • Low Temperature Reoxidation Mechanism in Nanocrystalline TiO2 − δ Thin Films
    Journal of The Electrochemical Society, 2001
    Co-Authors: Avner Rothschild, Y Komem, F Cosandey
    Abstract:

    This paper deals with the Reoxidation of nanocrystalline TiO 2 δ thin films during exposure to ambient oxygen at relatively low temperatures. A phenomenological model is proposed to describe the Reoxidation mechanism and its influence on the electrical conductance's sensitivity to oxygen, taking into account both surface and bulk processes. Chemisorption of oxygen predominates during the lirst few minutes, followed by diffusion of oxygen into the film and recombination with oxygen vacancies. The model describes the kinetics of the change in the electrical conductance during the transition from the initial to the final equilibrium states. Logarithmic and modified parabolic laws are derived to describe the change in the conductance as a function of time during the first (surface-controlled) and second (bulk-controlled) stages of the Reoxidation reaction, respectively. It is demonstrated that these expressions fit very well with experimental results from nanocrystalline TiO 2 δ thin films during exposure to ambien oxygen at constant temperatures between 200 and 325°C.