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Stefan Baumann - One of the best experts on this subject based on the ideXlab platform.
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Optimization of sintering conditions for improved microstructural and mechanical properties of dense Ce0.8Gd0.2O2-δ-FeCo2O4 Oxygen Transport Membranes
Journal of the European Ceramic Society, 2021Co-Authors: Fanlin Zeng, Jürgen Malzbender, Stefan Baumann, Olivier Guillon, Arian Nijmeijer, Louis Winnubst, Mirko Ziegner, Ruth Schwaiger, Wilhelm A. MeulenbergAbstract:Abstract Ce0.8Gd0.2O2-δ-FeCo2O4 composite is an excellent Oxygen Transport Membrane material with good chemical stability for applications in Oxygen separation and Membrane reactors. To improve microstructural and mechanical properties, sintering profiles for Ce0.8Gd0.2O2-δ-FeCo2O4 composites were optimized. Different sintering temperatures are selected based on our study of phase interactions among the initial powder mixtures using high-temperature X-ray diffraction. The results reveal that the phase interaction at ∼1050 ℃ accelerates densification process, and a further increase of sintering temperature to 1200 ℃ contributes to the homogenization of the pore distribution. A higher density and an improved homogeneity of pore distribution result in enhanced mechanical strength. However, the density decreases once the sintering temperature reaches 1350 ℃. Hence, the optimal sintering temperature considering both microstructural and mechanical properties appears to be 1200 ℃. Sintering at this temperature results in a microstructure with a density exceeding 99 % with only small surface defects and a high average flexural strength of approximately 266 MPa.
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chemical environment induced mixed conductivity of titanate as a highly stable Oxygen Transport Membrane
iScience, 2019Co-Authors: Wenyuan Liang, Heqing Jiang, Stefan Baumann, Wilhelm A. Meulenberg, Chih Long Tsai, Xiaoliang XiaAbstract:Summary Coupling of two Oxygen-involved reactions at the opposite sides of an Oxygen Transport Membrane (OTM) has demonstrated great potential for process intensification. However, the current cobalt- or iron-containing OTMs suffer from poor reduction tolerance, which are incompetent for Membrane reactor working in low Oxygen partial pressure (pO2). Here, we report for the first time a both Co- and Fe-free SrMg0.15Zr0.05Ti0.8O3−δ (SMZ-Ti) Membrane that exhibits both superior reduction tolerance for 100 h in 20 vol.% H2/Ar and environment-induced mixed conductivity due to the modest reduction of Ti4+ to Ti3+ in low pO2. We further demonstrate that SMZ-Ti is ideally suited for Membrane reactor where water splitting is coupled with methane reforming at the opposite sides to simultaneously obtain hydrogen and synthesis gas. These results extend the scope of mixed conducting materials to include titanates and open up new avenues for the design of chemically stable Membrane materials for high-performance Membrane reactors.
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Temperature-Induced Structural Reorganization of W-Doped Ba0.5Sr0.5Co0.8Fe0.2O3−δ Composite Membranes for Air Separation
Chemistry of Materials, 2019Co-Authors: Qianqian Lan, Stefan Baumann, Yoo Jung Sohn, Wilhelm A. Meulenberg, Rafal E. Dunin-borkowski, Heqing JiangAbstract:The practical use of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) prototypical Oxygen-Transport Membrane for air separation is currently hampered by the decomposition of the cubic perovskite into a variant with...
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Thermochemical stability of Fe- and co-functionalized perovskite-type SrTiO3 Oxygen Transport Membrane materials in syngas conditions
Journal of the European Ceramic Society, 2019Co-Authors: Yang Liu, Stefan Baumann, Yoo Jung Sohn, Vladimir Motalov, D. Sergeev, Michael Müller, Olivier GuillonAbstract:Abstract The materials typically used for Oxygen Transport Membranes, Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) tend to decompose due to their low thermochemical stability under reducing atmosphere. Fe- and Co-doped SrTiO3 (SrTi1-x-yCoxFeyO3-δ, x + y ≤ 0.35) (STCF) materials showing an Oxygen Transport comparable to LSCF have great potential for application in ion-Transport-devices. In this study, the thermochemical stability of pure perovskite-structured STCF was investigated after annealing in a syngas atmosphere at 600–900 °C. The phase composition of the materials after annealing was characterized by means of X-ray diffraction (XRD). The thermodynamic activities of SrO, FeO, and CoO in the STCF materials were evaluated using Knudsen effusion mass spectrometry (KEMS). Co-doped SrTiO3 (STC) materials were not stable after annealing in the syngas atmosphere above 5 mol% Co-substitution. Ruddlesden-Popper-like phases and SrCO3 were detected after annealing at 600 °C. In contrast, Fe substitution (STF) showed good stability after annealing in syngas upto 35 mol% substitution.
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Simulation of the effect of the porous support on flux through an asymmetric Oxygen Transport Membrane
Journal of Membrane Science, 2017Co-Authors: Unoaku Victoria Unije, Stefan Baumann, Robert Mücke, Patrick Niehoff, Robert Vaßen, Olivier GuillonAbstract:Abstract Asymmetric Membranes provide a low ionic resistance of the functional separation layer together with a high mechanical stability. However, the microstructure of the porous support in the Membrane assembly affects the overall flux significantly. This effect was studied by applying the binary friction model (BFM) for the support together with a modified Wagner equation for the dense Membrane using Transport relevant parameters obtained from micro computed tomography data of a tape cast Ba0.5Sr0.5Co0.8Fe0.2O3–δ support. The influence of different pore diameters and thicknesses of the support were compared for different feed gases (Oxygen and air) and flow configurations (3-end, 4-end, assembly orientation). The effect of the support at large pore diameters (>35 µm) for the 3-end mode Transport process using Oxygen as feed gas, was negligible. This was not the case for the 4-end mode irrespective of the feed gas, and for the 3-end mode using air as feed gas. This was attributed to the binary diffusion term in the BFM. Thin small-pored supports yield the same flux as thick large-pored supports considering a non-linear relationship between thickness and pore size. This can be used for the optimization of the support's microstructure with regards to mechanical strength and permeability.
Wilhelm A. Meulenberg - One of the best experts on this subject based on the ideXlab platform.
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Optimization of sintering conditions for improved microstructural and mechanical properties of dense Ce0.8Gd0.2O2-δ-FeCo2O4 Oxygen Transport Membranes
Journal of the European Ceramic Society, 2021Co-Authors: Fanlin Zeng, Jürgen Malzbender, Stefan Baumann, Olivier Guillon, Arian Nijmeijer, Louis Winnubst, Mirko Ziegner, Ruth Schwaiger, Wilhelm A. MeulenbergAbstract:Abstract Ce0.8Gd0.2O2-δ-FeCo2O4 composite is an excellent Oxygen Transport Membrane material with good chemical stability for applications in Oxygen separation and Membrane reactors. To improve microstructural and mechanical properties, sintering profiles for Ce0.8Gd0.2O2-δ-FeCo2O4 composites were optimized. Different sintering temperatures are selected based on our study of phase interactions among the initial powder mixtures using high-temperature X-ray diffraction. The results reveal that the phase interaction at ∼1050 ℃ accelerates densification process, and a further increase of sintering temperature to 1200 ℃ contributes to the homogenization of the pore distribution. A higher density and an improved homogeneity of pore distribution result in enhanced mechanical strength. However, the density decreases once the sintering temperature reaches 1350 ℃. Hence, the optimal sintering temperature considering both microstructural and mechanical properties appears to be 1200 ℃. Sintering at this temperature results in a microstructure with a density exceeding 99 % with only small surface defects and a high average flexural strength of approximately 266 MPa.
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chemical environment induced mixed conductivity of titanate as a highly stable Oxygen Transport Membrane
iScience, 2019Co-Authors: Wenyuan Liang, Heqing Jiang, Stefan Baumann, Wilhelm A. Meulenberg, Chih Long Tsai, Xiaoliang XiaAbstract:Summary Coupling of two Oxygen-involved reactions at the opposite sides of an Oxygen Transport Membrane (OTM) has demonstrated great potential for process intensification. However, the current cobalt- or iron-containing OTMs suffer from poor reduction tolerance, which are incompetent for Membrane reactor working in low Oxygen partial pressure (pO2). Here, we report for the first time a both Co- and Fe-free SrMg0.15Zr0.05Ti0.8O3−δ (SMZ-Ti) Membrane that exhibits both superior reduction tolerance for 100 h in 20 vol.% H2/Ar and environment-induced mixed conductivity due to the modest reduction of Ti4+ to Ti3+ in low pO2. We further demonstrate that SMZ-Ti is ideally suited for Membrane reactor where water splitting is coupled with methane reforming at the opposite sides to simultaneously obtain hydrogen and synthesis gas. These results extend the scope of mixed conducting materials to include titanates and open up new avenues for the design of chemically stable Membrane materials for high-performance Membrane reactors.
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Temperature-Induced Structural Reorganization of W-Doped Ba0.5Sr0.5Co0.8Fe0.2O3−δ Composite Membranes for Air Separation
Chemistry of Materials, 2019Co-Authors: Qianqian Lan, Stefan Baumann, Yoo Jung Sohn, Wilhelm A. Meulenberg, Rafal E. Dunin-borkowski, Heqing JiangAbstract:The practical use of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) prototypical Oxygen-Transport Membrane for air separation is currently hampered by the decomposition of the cubic perovskite into a variant with...
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structural and functional properties of srti1 xfexo3 δ 0 x 1 for the use as Oxygen Transport Membrane
Separation and Purification Technology, 2015Co-Authors: Falk Schulzekuppers, S.f.p. Ten Donkelaar, Stefan Baumann, P. Prigorodov, Yoo Jung Sohn, Henny J.m. Bouwmeester, Wilhelm A. Meulenberg, Olivier GuillonAbstract:Abstract Perovskitic oxides are widely investigated as Oxygen Transport Membrane materials for the efficient generation of pure Oxygen or the use in Membrane reactors. However, most of high performance perovskites suffer from low stability in operation conditions. Therefore, solid solutions of SrTi 1 − x Fe x O 3 − δ (STF) are investigated due to the initial high stability of the strontium titanate host lattice. Self-synthesized powders with substitution of Ti by 0%, 25%, 35%, 50%, 75%, and 100% Fe were studied. Crystal structure, functional properties i.e., diffusion coefficient, surface exchange rates, and Oxygen permeation rates as well as Membrane fabrication and operation related material properties i.e. sintering behaviour and thermal/chemical expansion were investigated. Substitution of Ti by Fe increases Oxygen mobility and, hence, Oxygen permeation rates, but reduces stability in operation relevant atmospheres such as Ar/4%H 2 or CO 2 . At the same time thermal/chemical expansion increases. This makes the fabrication of supported thin Membranes and their integration into Membrane modules more challenging. It turned out that 25–35% Fe substituting Ti seems to be a good compromise between structural and functional properties. Oxygen permeation rates achieved are comparable to that of standard materials such as La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 − δ (LSCF). At the same time stability is higher and thermal expansion coefficients lower compared to LSCF, which makes STF with limited Fe-content (max. 35%) a promising Oxygen Transport Membrane material.
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Structural and functional properties of SrTi1−xFexO3−δ (0⩽x⩽1) for the use as Oxygen Transport Membrane
Separation and Purification Technology, 2015Co-Authors: Falk Schulze-küppers, S.f.p. Ten Donkelaar, Stefan Baumann, P. Prigorodov, Yoo Jung Sohn, Henny J.m. Bouwmeester, Wilhelm A. Meulenberg, Olivier GuillonAbstract:Abstract Perovskitic oxides are widely investigated as Oxygen Transport Membrane materials for the efficient generation of pure Oxygen or the use in Membrane reactors. However, most of high performance perovskites suffer from low stability in operation conditions. Therefore, solid solutions of SrTi 1 − x Fe x O 3 − δ (STF) are investigated due to the initial high stability of the strontium titanate host lattice. Self-synthesized powders with substitution of Ti by 0%, 25%, 35%, 50%, 75%, and 100% Fe were studied. Crystal structure, functional properties i.e., diffusion coefficient, surface exchange rates, and Oxygen permeation rates as well as Membrane fabrication and operation related material properties i.e. sintering behaviour and thermal/chemical expansion were investigated. Substitution of Ti by Fe increases Oxygen mobility and, hence, Oxygen permeation rates, but reduces stability in operation relevant atmospheres such as Ar/4%H 2 or CO 2 . At the same time thermal/chemical expansion increases. This makes the fabrication of supported thin Membranes and their integration into Membrane modules more challenging. It turned out that 25–35% Fe substituting Ti seems to be a good compromise between structural and functional properties. Oxygen permeation rates achieved are comparable to that of standard materials such as La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 − δ (LSCF). At the same time stability is higher and thermal expansion coefficients lower compared to LSCF, which makes STF with limited Fe-content (max. 35%) a promising Oxygen Transport Membrane material.
Kati Raju - One of the best experts on this subject based on the ideXlab platform.
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rietveld refinement and estimation of residual stress in gdc lscf Oxygen Transport Membrane ceramic composites
Ceramics International, 2018Co-Authors: Kati Raju, Seyoung Kim, Soo-hyun Kim, Young-hoon Seong, In-sub HanAbstract:Abstract The phase purity and crystal structure of dual-phase Ce .9 Gd .1 O 2–δ –La .6 Sr .4 Co .2 Fe .8 O 3–δ (GDC–LSCF) composites were refined using data obtained from X-ray diffraction (XRD) by employing the Rietveld method. Rietveld analysis indicated that the structures of GDC and LSCF phases are well crystallized as cubic Fm 3 m and rhombohedral R 3 c space groups, respectively. Scanning electron microscopy images showed smooth and dense structures, depicting a homogeneous crystalline structure of the samples. When the composites were cooled from their sintering temperature (1250 °C), compressive stresses were generated in the GDC and corresponding tensile stresses were generated in the LSCF due to differences in thermal expansion coefficients. The compressive residual stresses of the composites were investigated by high-angle XRD measurements using the well-known sin 2 ψ method. The average compressive residual stresses in GDC phase are estimated to be − 312 and − 290 MPa for 80 GDC–20 LSCF and 50 GDC–50 LSCF, respectively. The aim of this study is to provide a better understanding of the crystal structures and residual stresses in GDC–LSCF composites through XRD and the suitability of these composites for Oxygen Transport Membranes.
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Interfacial microstructure and shear strength of reactive air brazed Oxygen Transport Membrane ceramic-metal alloy joints
Metals and Materials International, 2018Co-Authors: Dang-hyok Yoon, Seyoung Kim, Kati Raju, Kwang-sup SongAbstract:To fabricate a multi-layered structure for maximizing Oxygen production, Oxygen Transport Membrane (OTM) ceramics need to be joined or sealed hermetically metal supports for interfacing with the peripheral components of the system. Therefore, in this study, Ag–10 wt% CuO was evaluated as an effective filler material for the reactive air brazing of dense Ce0.9Gd0.1O2–δ–La0.7Sr0.3MnO3±δ (GDC–LSM) OTM ceramics. Thermal decomposition in air and wetting behavior of the braze filler was performed. Reactive air brazing was performed at 1050 °C for 30 min in air to join GDC–LSM with four different commercially available high temperature-resistant metal alloys, such as Crofer 22 APU, Inconel 600, Fecralloy, and AISI 310S. The microstructure and elemental distribution of the ceramic-ceramic and ceramic-metal interfaces were examined from polished cross-sections. The mechanical shear strength at room temperature for the as-brazed and isothermally aged (800 °C for 24 h) joints of all the samples was compared. The results showed that the strength of the ceramic-ceramic joints was decreased marginally by aging; however, in the case of metal-ceramic joints, different decreases in strengths were observed according to the metal alloy used, which was explained based on the formation of different oxide layers at the interfaces.
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Interfacial microstructure and shear strength of reactive air brazed Oxygen Transport Membrane ceramic–metal alloy joints
Metals and Materials International, 2018Co-Authors: Dang-hyok Yoon, Seyoung Kim, Kati Raju, Kwang-sup SongAbstract:To fabricate a multi-layered structure for maximizing Oxygen production, Oxygen Transport Membrane (OTM) ceramics need to be joined or sealed hermetically metal supports for interfacing with the peripheral components of the system. Therefore, in this study, Ag–10 wt% CuO was evaluated as an effective filler material for the reactive air brazing of dense Ce_0.9Gd_0.1O_2–δ–La_0.7Sr_0.3MnO_3±δ (GDC–LSM) OTM ceramics. Thermal decomposition in air and wetting behavior of the braze filler was performed. Reactive air brazing was performed at 1050 °C for 30 min in air to join GDC–LSM with four different commercially available high temperature-resistant metal alloys, such as Crofer 22 APU, Inconel 600, Fecralloy, and AISI 310S. The microstructure and elemental distribution of the ceramic-ceramic and ceramic-metal interfaces were examined from polished cross-sections. The mechanical shear strength at room temperature for the as-brazed and isothermally aged (800 °C for 24 h) joints of all the samples was compared. The results showed that the strength of the ceramic-ceramic joints was decreased marginally by aging; however, in the case of metal-ceramic joints, different decreases in strengths were observed according to the metal alloy used, which was explained based on the formation of different oxide layers at the interfaces.
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Rietveld refinement and estimation of residual stress in GDC–LSCF Oxygen Transport Membrane ceramic composites
Ceramics International, 2018Co-Authors: Kati Raju, Seyoung Kim, Soo-hyun Kim, Young-hoon Seong, In-sub HanAbstract:Abstract The phase purity and crystal structure of dual-phase Ce .9 Gd .1 O 2–δ –La .6 Sr .4 Co .2 Fe .8 O 3–δ (GDC–LSCF) composites were refined using data obtained from X-ray diffraction (XRD) by employing the Rietveld method. Rietveld analysis indicated that the structures of GDC and LSCF phases are well crystallized as cubic Fm 3 m and rhombohedral R 3 c space groups, respectively. Scanning electron microscopy images showed smooth and dense structures, depicting a homogeneous crystalline structure of the samples. When the composites were cooled from their sintering temperature (1250 °C), compressive stresses were generated in the GDC and corresponding tensile stresses were generated in the LSCF due to differences in thermal expansion coefficients. The compressive residual stresses of the composites were investigated by high-angle XRD measurements using the well-known sin 2 ψ method. The average compressive residual stresses in GDC phase are estimated to be − 312 and − 290 MPa for 80 GDC–20 LSCF and 50 GDC–50 LSCF, respectively. The aim of this study is to provide a better understanding of the crystal structures and residual stresses in GDC–LSCF composites through XRD and the suitability of these composites for Oxygen Transport Membranes.
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reactive air brazing of gdc lscf ceramics using ag 10 wt cuo paste for Oxygen Transport Membrane applications
Ceramics International, 2016Co-Authors: Kati Raju, Dang-hyok YoonAbstract:Abstract This paper reports the effectiveness of a Ag–10 wt% CuO braze filler for the joining of dense Ce 0.9 Gd 0.1 O 2–δ –La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3–δ (GDC–LSCF) dual-phase ceramics for the Oxygen Transport Membrane applications. Brazing was performed at 1050 °C for 30 min in air. The microstructure of the ceramic-filler-ceramic interfaces of the polished cross-sectional areas and the elemental distribution were examined. The results indicated that the Ag–10 wt% CuO braze filler ensured reliable and compact joining without the formation of cracks and voids at the joining interface. The room temperature mechanical shear strengths were 59.3 and 40.2 MPa for the as-brazed and isothermally aged joints at 800 °C for 24 h in air, respectively.
Dang-hyok Yoon - One of the best experts on this subject based on the ideXlab platform.
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Interfacial microstructure and shear strength of reactive air brazed Oxygen Transport Membrane ceramic-metal alloy joints
Metals and Materials International, 2018Co-Authors: Dang-hyok Yoon, Seyoung Kim, Kati Raju, Kwang-sup SongAbstract:To fabricate a multi-layered structure for maximizing Oxygen production, Oxygen Transport Membrane (OTM) ceramics need to be joined or sealed hermetically metal supports for interfacing with the peripheral components of the system. Therefore, in this study, Ag–10 wt% CuO was evaluated as an effective filler material for the reactive air brazing of dense Ce0.9Gd0.1O2–δ–La0.7Sr0.3MnO3±δ (GDC–LSM) OTM ceramics. Thermal decomposition in air and wetting behavior of the braze filler was performed. Reactive air brazing was performed at 1050 °C for 30 min in air to join GDC–LSM with four different commercially available high temperature-resistant metal alloys, such as Crofer 22 APU, Inconel 600, Fecralloy, and AISI 310S. The microstructure and elemental distribution of the ceramic-ceramic and ceramic-metal interfaces were examined from polished cross-sections. The mechanical shear strength at room temperature for the as-brazed and isothermally aged (800 °C for 24 h) joints of all the samples was compared. The results showed that the strength of the ceramic-ceramic joints was decreased marginally by aging; however, in the case of metal-ceramic joints, different decreases in strengths were observed according to the metal alloy used, which was explained based on the formation of different oxide layers at the interfaces.
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Interfacial microstructure and shear strength of reactive air brazed Oxygen Transport Membrane ceramic–metal alloy joints
Metals and Materials International, 2018Co-Authors: Dang-hyok Yoon, Seyoung Kim, Kati Raju, Kwang-sup SongAbstract:To fabricate a multi-layered structure for maximizing Oxygen production, Oxygen Transport Membrane (OTM) ceramics need to be joined or sealed hermetically metal supports for interfacing with the peripheral components of the system. Therefore, in this study, Ag–10 wt% CuO was evaluated as an effective filler material for the reactive air brazing of dense Ce_0.9Gd_0.1O_2–δ–La_0.7Sr_0.3MnO_3±δ (GDC–LSM) OTM ceramics. Thermal decomposition in air and wetting behavior of the braze filler was performed. Reactive air brazing was performed at 1050 °C for 30 min in air to join GDC–LSM with four different commercially available high temperature-resistant metal alloys, such as Crofer 22 APU, Inconel 600, Fecralloy, and AISI 310S. The microstructure and elemental distribution of the ceramic-ceramic and ceramic-metal interfaces were examined from polished cross-sections. The mechanical shear strength at room temperature for the as-brazed and isothermally aged (800 °C for 24 h) joints of all the samples was compared. The results showed that the strength of the ceramic-ceramic joints was decreased marginally by aging; however, in the case of metal-ceramic joints, different decreases in strengths were observed according to the metal alloy used, which was explained based on the formation of different oxide layers at the interfaces.
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reactive air brazing of gdc lscf ceramics using ag 10 wt cuo paste for Oxygen Transport Membrane applications
Ceramics International, 2016Co-Authors: Kati Raju, Dang-hyok YoonAbstract:Abstract This paper reports the effectiveness of a Ag–10 wt% CuO braze filler for the joining of dense Ce 0.9 Gd 0.1 O 2–δ –La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3–δ (GDC–LSCF) dual-phase ceramics for the Oxygen Transport Membrane applications. Brazing was performed at 1050 °C for 30 min in air. The microstructure of the ceramic-filler-ceramic interfaces of the polished cross-sectional areas and the elemental distribution were examined. The results indicated that the Ag–10 wt% CuO braze filler ensured reliable and compact joining without the formation of cracks and voids at the joining interface. The room temperature mechanical shear strengths were 59.3 and 40.2 MPa for the as-brazed and isothermally aged joints at 800 °C for 24 h in air, respectively.
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Joining of metal-ceramic using reactive air brazing for Oxygen Transport Membrane applications
Materials and Design, 2016Co-Authors: Kati Raju, Seyoung Kim, Ji Haeng Yu, Kwang-sup Song, Dang-hyok YoonAbstract:This study examined the joining of dense Ce0.9Gd0.1O2 − δ–La0.6Sr0.4Co0.2Fe0.8O3 − δ(GDC–LSCF) ceramics to high temperature metal alloys for the fabrication of multilayered Oxygen Transport Membrane (OTM) stacks. Reactive air brazing using a silver-based paste was performed at 1050 °C for 30 min in air to join GDC–LSCF/high temperature alloys, such as AISI 310S, Inconel 600 and Crofer 22 APU. The effects of the various filler materials, including CuO, GDC, LSCF, and GDC–LSCF mixture, in the Ag paste were also examined. The Ag–10 wt% CuO braze filler ensured in a reliable and compact joining without the formation of cracks and voids at the joining interface, while the addition of other ceramic fillers resulted in incomplete joining. Although none of the GDC–LSCF/metal alloy joints showed gas leakage at room temperature, the GDC–LSCF/Crofer joint only maintained the gas-tightness up to 800 °C under pressurized air up to 7 bars, which was explained by the microstructural rigidness of the oxide layer formed on the filler/alloy interface at high temperatures. This was supported by the minimal decrease in shear strength of the GDC–LSCF/Crofer joint, which was 91.1 and 88.3 MPa for the as-brazed and isothermally aged joint at 800 °C for 24 h in air, respectively.
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Reactive air brazing of GDC–LSCF ceramics using Ag–10 wt% CuO paste for Oxygen Transport Membrane applications
Ceramics International, 2016Co-Authors: Kati Raju, Muksin, Dang-hyok YoonAbstract:Abstract This paper reports the effectiveness of a Ag–10 wt% CuO braze filler for the joining of dense Ce 0.9 Gd 0.1 O 2–δ –La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3–δ (GDC–LSCF) dual-phase ceramics for the Oxygen Transport Membrane applications. Brazing was performed at 1050 °C for 30 min in air. The microstructure of the ceramic-filler-ceramic interfaces of the polished cross-sectional areas and the elemental distribution were examined. The results indicated that the Ag–10 wt% CuO braze filler ensured reliable and compact joining without the formation of cracks and voids at the joining interface. The room temperature mechanical shear strengths were 59.3 and 40.2 MPa for the as-brazed and isothermally aged joints at 800 °C for 24 h in air, respectively.
Olivier Guillon - One of the best experts on this subject based on the ideXlab platform.
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Optimization of sintering conditions for improved microstructural and mechanical properties of dense Ce0.8Gd0.2O2-δ-FeCo2O4 Oxygen Transport Membranes
Journal of the European Ceramic Society, 2021Co-Authors: Fanlin Zeng, Jürgen Malzbender, Stefan Baumann, Olivier Guillon, Arian Nijmeijer, Louis Winnubst, Mirko Ziegner, Ruth Schwaiger, Wilhelm A. MeulenbergAbstract:Abstract Ce0.8Gd0.2O2-δ-FeCo2O4 composite is an excellent Oxygen Transport Membrane material with good chemical stability for applications in Oxygen separation and Membrane reactors. To improve microstructural and mechanical properties, sintering profiles for Ce0.8Gd0.2O2-δ-FeCo2O4 composites were optimized. Different sintering temperatures are selected based on our study of phase interactions among the initial powder mixtures using high-temperature X-ray diffraction. The results reveal that the phase interaction at ∼1050 ℃ accelerates densification process, and a further increase of sintering temperature to 1200 ℃ contributes to the homogenization of the pore distribution. A higher density and an improved homogeneity of pore distribution result in enhanced mechanical strength. However, the density decreases once the sintering temperature reaches 1350 ℃. Hence, the optimal sintering temperature considering both microstructural and mechanical properties appears to be 1200 ℃. Sintering at this temperature results in a microstructure with a density exceeding 99 % with only small surface defects and a high average flexural strength of approximately 266 MPa.
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Thermochemical stability of Fe- and co-functionalized perovskite-type SrTiO3 Oxygen Transport Membrane materials in syngas conditions
Journal of the European Ceramic Society, 2019Co-Authors: Yang Liu, Stefan Baumann, Yoo Jung Sohn, Vladimir Motalov, D. Sergeev, Michael Müller, Olivier GuillonAbstract:Abstract The materials typically used for Oxygen Transport Membranes, Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) tend to decompose due to their low thermochemical stability under reducing atmosphere. Fe- and Co-doped SrTiO3 (SrTi1-x-yCoxFeyO3-δ, x + y ≤ 0.35) (STCF) materials showing an Oxygen Transport comparable to LSCF have great potential for application in ion-Transport-devices. In this study, the thermochemical stability of pure perovskite-structured STCF was investigated after annealing in a syngas atmosphere at 600–900 °C. The phase composition of the materials after annealing was characterized by means of X-ray diffraction (XRD). The thermodynamic activities of SrO, FeO, and CoO in the STCF materials were evaluated using Knudsen effusion mass spectrometry (KEMS). Co-doped SrTiO3 (STC) materials were not stable after annealing in the syngas atmosphere above 5 mol% Co-substitution. Ruddlesden-Popper-like phases and SrCO3 were detected after annealing at 600 °C. In contrast, Fe substitution (STF) showed good stability after annealing in syngas upto 35 mol% substitution.
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Simulation of the effect of the porous support on flux through an asymmetric Oxygen Transport Membrane
Journal of Membrane Science, 2017Co-Authors: Unoaku Victoria Unije, Stefan Baumann, Robert Mücke, Patrick Niehoff, Robert Vaßen, Olivier GuillonAbstract:Abstract Asymmetric Membranes provide a low ionic resistance of the functional separation layer together with a high mechanical stability. However, the microstructure of the porous support in the Membrane assembly affects the overall flux significantly. This effect was studied by applying the binary friction model (BFM) for the support together with a modified Wagner equation for the dense Membrane using Transport relevant parameters obtained from micro computed tomography data of a tape cast Ba0.5Sr0.5Co0.8Fe0.2O3–δ support. The influence of different pore diameters and thicknesses of the support were compared for different feed gases (Oxygen and air) and flow configurations (3-end, 4-end, assembly orientation). The effect of the support at large pore diameters (>35 µm) for the 3-end mode Transport process using Oxygen as feed gas, was negligible. This was not the case for the 4-end mode irrespective of the feed gas, and for the 3-end mode using air as feed gas. This was attributed to the binary diffusion term in the BFM. Thin small-pored supports yield the same flux as thick large-pored supports considering a non-linear relationship between thickness and pore size. This can be used for the optimization of the support's microstructure with regards to mechanical strength and permeability.
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structural and functional properties of srti1 xfexo3 δ 0 x 1 for the use as Oxygen Transport Membrane
Separation and Purification Technology, 2015Co-Authors: Falk Schulzekuppers, S.f.p. Ten Donkelaar, Stefan Baumann, P. Prigorodov, Yoo Jung Sohn, Henny J.m. Bouwmeester, Wilhelm A. Meulenberg, Olivier GuillonAbstract:Abstract Perovskitic oxides are widely investigated as Oxygen Transport Membrane materials for the efficient generation of pure Oxygen or the use in Membrane reactors. However, most of high performance perovskites suffer from low stability in operation conditions. Therefore, solid solutions of SrTi 1 − x Fe x O 3 − δ (STF) are investigated due to the initial high stability of the strontium titanate host lattice. Self-synthesized powders with substitution of Ti by 0%, 25%, 35%, 50%, 75%, and 100% Fe were studied. Crystal structure, functional properties i.e., diffusion coefficient, surface exchange rates, and Oxygen permeation rates as well as Membrane fabrication and operation related material properties i.e. sintering behaviour and thermal/chemical expansion were investigated. Substitution of Ti by Fe increases Oxygen mobility and, hence, Oxygen permeation rates, but reduces stability in operation relevant atmospheres such as Ar/4%H 2 or CO 2 . At the same time thermal/chemical expansion increases. This makes the fabrication of supported thin Membranes and their integration into Membrane modules more challenging. It turned out that 25–35% Fe substituting Ti seems to be a good compromise between structural and functional properties. Oxygen permeation rates achieved are comparable to that of standard materials such as La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 − δ (LSCF). At the same time stability is higher and thermal expansion coefficients lower compared to LSCF, which makes STF with limited Fe-content (max. 35%) a promising Oxygen Transport Membrane material.
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Structural and functional properties of SrTi1−xFexO3−δ (0⩽x⩽1) for the use as Oxygen Transport Membrane
Separation and Purification Technology, 2015Co-Authors: Falk Schulze-küppers, S.f.p. Ten Donkelaar, Stefan Baumann, P. Prigorodov, Yoo Jung Sohn, Henny J.m. Bouwmeester, Wilhelm A. Meulenberg, Olivier GuillonAbstract:Abstract Perovskitic oxides are widely investigated as Oxygen Transport Membrane materials for the efficient generation of pure Oxygen or the use in Membrane reactors. However, most of high performance perovskites suffer from low stability in operation conditions. Therefore, solid solutions of SrTi 1 − x Fe x O 3 − δ (STF) are investigated due to the initial high stability of the strontium titanate host lattice. Self-synthesized powders with substitution of Ti by 0%, 25%, 35%, 50%, 75%, and 100% Fe were studied. Crystal structure, functional properties i.e., diffusion coefficient, surface exchange rates, and Oxygen permeation rates as well as Membrane fabrication and operation related material properties i.e. sintering behaviour and thermal/chemical expansion were investigated. Substitution of Ti by Fe increases Oxygen mobility and, hence, Oxygen permeation rates, but reduces stability in operation relevant atmospheres such as Ar/4%H 2 or CO 2 . At the same time thermal/chemical expansion increases. This makes the fabrication of supported thin Membranes and their integration into Membrane modules more challenging. It turned out that 25–35% Fe substituting Ti seems to be a good compromise between structural and functional properties. Oxygen permeation rates achieved are comparable to that of standard materials such as La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 − δ (LSCF). At the same time stability is higher and thermal expansion coefficients lower compared to LSCF, which makes STF with limited Fe-content (max. 35%) a promising Oxygen Transport Membrane material.
