{"id":{"repo_id":"aachen","oai_identifier":"oai:publications.rwth-aachen.de:50579"},"canonical_url":"https://search.dev.ndltd.org/etd/aachen/oai:publications.rwth-aachen.de:50579","repository":{"repo_id":"aachen","name":"RWTH Aachen University","base_url":"https://publications.rwth-aachen.de/oai2d"},"display":{"title":"Oxygen transport in Ba(Fe,Co,Zr)O 3 - delta membranes","abstract":"The nonstoichiometry of Ba(Fe,Co,Zr)O3-delta (Zr-lean Ba(Fe,Co,Zr)O3-delta) is measured as a function of temperature and oxygen activity by TG. Very high nonstoichiometry (delta0=0.78 at a(O2)=1) is determined at 1273 K. From the nonstoichiometry of Ba(Fe,Co,Zr)O3-delta;, exponent n (n=-0.01) in Cv=C0v•a(O2)n, thermodynamic factor (gamma=140) and activation energy for oxygen vacancy formation (DeltaEf=1.5 kJ/mol) are estimated. Two oxygen transport models in Ba(Fe,Co,Zr)O3-delta membranes are proposed. In bulk, oxygen ion diffusion is described by the classical Wagner equation. At gas-solid interfaces, two models (two surface exchange reaction rates) are derived based on various surface exchange reaction kinetics. By combining two (oxygen ion diffusion in bulk and exchange reaction at gas-solid interfaces), two oxygen transport models, which have three parameters (oxygen ionic conductivity, sigma0ion, surface exchange coefficient, k, and the exponent n in Cv=C0v•a(O2)n.), are developed. Finally, sigma0ion and k are determined by fitting the oxygen permeation data to the two models using the exponent n determined by TG (n=-0.01). Oxygen permeation fluxes for Ba(Fe,Co,Zr)O3-delta membranes were measured as a function of temperature and oxygen activity on the sweep gas side. Thickness dependency of oxygen permeation (ag1=0.21 and ag2=0.02) shows clearly that oxygen permeation in Ba(Fe,Co,Zr)O3-delta membranes is partially controlled by surface exchange reaction. Using the exponent n (=-0.01) determined by TG, the remaining two parameters (sigma0ion, k) are determined by fitting the experimental data to the models. In terms of curvatures of flux lines calculated from both models, the second model seems to provide better description of oxygen permeation. However, there was no big difference in activation energies of sigma0ion and k, and the calculated characteristic length, Lc. When a new parameter, the dependency of surface exchange coefficient on oxygen activity (k=k0•ag(O2)m or k=k0•as(O2)m) is introduced to both models, reasonable values for sigma0ion, k, and m as well as higher fitting quality can be obtained. For both cases, the dependency of surface exchange coefficient on oxygen activity (m=0.80 for the first model and m=0.40 for the second model in k=k0•ag(O2)m), and m=1.55 for the first model and m=0.80 for the second model in k=k0•as(O2)m) is scattered roughly in the same range of the literature data (m=0.4~1.2). Oxygen permeation rates for fibre type membrane (wall thickness 0.16 mm) are measured as a function of temperature and sweep gas flow rate (Ar flow rate). Using a simple Wagner equation, overall activation energy of oxygen transport across a fibre type Ba(Fe,Co,Zr)O3-delta membrane is evaluated, which lies between two activation energies obtained for disc type membrane. This confirms that very reasonable values for sigma0ion and k were obtained for disc type membrane. More quantitatively, the oxygen permeation rates of a fibre type membrane are calculated using the parameters obtained from disc type membrane. The calculated oxygen permeation rates of a fibre type membrane do not deviate so much from the experimental data. The calculation results show further that the presence of bubbles (or pores) can reduce the oxygen permeation rates of fibre type membrane and the total oxygen permeation rates of fibre type membrane are higher in counter-current that in co-current. Overlap of TG relaxation curves of 0.42 mm thick membrane with that of 0.13 mm thick membrane means that intrinsic relaxation induced by Dchem and kchem is so fast and the response of TG furnace is so slow that it is impossible to discern TG relaxation curves of two membranes from the response of TG furnace. Comparison of the response of TG furnace (directly measured by oxygen sensor) with the relaxation curve of two membranes strongly shows that the relaxation is controlled entirely by the response of TG furnace. In this case, the only minimum Dchem and kchem can be estimated by assuming a certain error boundary (xi) of the response of TG furnace. A parametric study shows that Dchem and kchem determined from single relaxation curve might include high errors. This provides two requirements for extraction of accurate Dchem and kchem: at least two relaxation curves should be obtained from two membranes and they should belong to different L/Lc regime.","abstract_html":"The nonstoichiometry of Ba(Fe,Co,Zr)O3-delta (Zr-lean Ba(Fe,Co,Zr)O3-delta) is measured as a function of temperature and oxygen activity by TG. Very high nonstoichiometry (delta0=0.78 at a(O2)=1) is determined at 1273 K. From the nonstoichiometry of Ba(Fe,Co,Zr)O3-delta;, exponent n (n=-0.01) in Cv=C0v•a(O2)n, thermodynamic factor (gamma=140) and activation energy for oxygen vacancy formation (DeltaEf=1.5 kJ/mol) are estimated. Two oxygen transport models in Ba(Fe,Co,Zr)O3-delta membranes are proposed. In bulk, oxygen ion diffusion is described by the classical Wagner equation. At gas-solid interfaces, two models (two surface exchange reaction rates) are derived based on various surface exchange reaction kinetics. By combining two (oxygen ion diffusion in bulk and exchange reaction at gas-solid interfaces), two oxygen transport models, which have three parameters (oxygen ionic conductivity, sigma0ion, surface exchange coefficient, k, and the exponent n in Cv=C0v•a(O2)n.), are developed. Finally, sigma0ion and k are determined by fitting the oxygen permeation data to the two models using the exponent n determined by TG (n=-0.01). Oxygen permeation fluxes for Ba(Fe,Co,Zr)O3-delta membranes were measured as a function of temperature and oxygen activity on the sweep gas side. Thickness dependency of oxygen permeation (ag1=0.21 and ag2=0.02) shows clearly that oxygen permeation in Ba(Fe,Co,Zr)O3-delta membranes is partially controlled by surface exchange reaction. Using the exponent n (=-0.01) determined by TG, the remaining two parameters (sigma0ion, k) are determined by fitting the experimental data to the models. In terms of curvatures of flux lines calculated from both models, the second model seems to provide better description of oxygen permeation. However, there was no big difference in activation energies of sigma0ion and k, and the calculated characteristic length, Lc. When a new parameter, the dependency of surface exchange coefficient on oxygen activity (k=k0•ag(O2)m or k=k0•as(O2)m) is introduced to both models, reasonable values for sigma0ion, k, and m as well as higher fitting quality can be obtained. For both cases, the dependency of surface exchange coefficient on oxygen activity (m=0.80 for the first model and m=0.40 for the second model in k=k0•ag(O2)m), and m=1.55 for the first model and m=0.80 for the second model in k=k0•as(O2)m) is scattered roughly in the same range of the literature data (m=0.4~1.2). Oxygen permeation rates for fibre type membrane (wall thickness 0.16 mm) are measured as a function of temperature and sweep gas flow rate (Ar flow rate). Using a simple Wagner equation, overall activation energy of oxygen transport across a fibre type Ba(Fe,Co,Zr)O3-delta membrane is evaluated, which lies between two activation energies obtained for disc type membrane. This confirms that very reasonable values for sigma0ion and k were obtained for disc type membrane. More quantitatively, the oxygen permeation rates of a fibre type membrane are calculated using the parameters obtained from disc type membrane. The calculated oxygen permeation rates of a fibre type membrane do not deviate so much from the experimental data. The calculation results show further that the presence of bubbles (or pores) can reduce the oxygen permeation rates of fibre type membrane and the total oxygen permeation rates of fibre type membrane are higher in counter-current that in co-current. Overlap of TG relaxation curves of 0.42 mm thick membrane with that of 0.13 mm thick membrane means that intrinsic relaxation induced by Dchem and kchem is so fast and the response of TG furnace is so slow that it is impossible to discern TG relaxation curves of two membranes from the response of TG furnace. Comparison of the response of TG furnace (directly measured by oxygen sensor) with the relaxation curve of two membranes strongly shows that the relaxation is controlled entirely by the response of TG furnace. In this case, the only minimum Dchem and kchem can be estimated by assuming a certain error boundary (xi) of the response of TG furnace. A parametric study shows that Dchem and kchem determined from single relaxation curve might include high errors. This provides two requirements for extraction of accurate Dchem and kchem: at least two relaxation curves should be obtained from two membranes and they should belong to different L/Lc regime.","abstract_has_math":false,"creators":["Byun, Young Chang"],"institution":"Publikationsserver der RWTH Aachen University","degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":["Schroeder, Michael"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2008,"date_issued":"2008","date_published":"2008","updated_at":"2026-07-30T19:40:25Z","subjects":["info:eu-repo/classification/ddc/540","Membran","Sauerstofftransport","Chemie","Sauerstofftrennung","oxygen separation","membrane"],"languages":["eng"],"rights":["info:eu-repo/semantics/openAccess"],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-113119%22"],"render_values":[{"text":"https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-113119%22","href":"https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-113119%22","code":true}]}]},"links":{"outbound_url":"https://publications.rwth-aachen.de/record/50579","outbound_label":"Repository record","outbound_source":"dc:identifier"},"source_record":{"url":"https://publications.rwth-aachen.de/oai2d?verb=GetRecord&metadataPrefix=oai_dc&identifier=oai%3Apublications.rwth-aachen.de%3A50579","prefix":"oai_dc"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Schroeder, Michael"]},{"key":"dc:creator","label":"Author","values":["Byun, Young Chang"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:coverage","label":"Dc Coverage","values":["DE"]},{"key":"dc:date","label":"Dc Date","values":["2008"]},{"key":"dc:publisher","label":"Institution","values":["Publikationsserver der RWTH Aachen University"]},{"key":"dc:relation","label":"Dc Relation","values":["info:eu-repo/semantics/altIdentifier/urn/urn:nbn:de:hbz:82-opus-26694"]},{"key":"dc:type","label":"Dc Type","values":["info:eu-repo/semantics/doctoralThesis","info:eu-repo/semantics/publishedVersion"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["info:eu-repo/classification/ddc/540","Membran","Sauerstofftransport","Chemie","Sauerstofftrennung","oxygen separation","membrane"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["eng"]},{"key":"dc:rights","label":"Dc Rights","values":["info:eu-repo/semantics/openAccess"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://publications.rwth-aachen.de/record/50579","https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-113119%22"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["The nonstoichiometry of Ba(Fe,Co,Zr)O3-delta (Zr-lean Ba(Fe,Co,Zr)O3-delta) is measured as a function of temperature and oxygen activity by TG. Very high nonstoichiometry (delta0=0.78 at a(O2)=1) is determined at 1273 K. From the nonstoichiometry of Ba(Fe,Co,Zr)O3-delta;, exponent n (n=-0.01) in Cv=C0v•a(O2)n, thermodynamic factor (gamma=140) and activation energy for oxygen vacancy formation (DeltaEf=1.5 kJ/mol) are estimated. Two oxygen transport models in Ba(Fe,Co,Zr)O3-delta membranes are proposed. In bulk, oxygen ion diffusion is described by the classical Wagner equation. At gas-solid interfaces, two models (two surface exchange reaction rates) are derived based on various surface exchange reaction kinetics. By combining two (oxygen ion diffusion in bulk and exchange reaction at gas-solid interfaces), two oxygen transport models, which have three parameters (oxygen ionic conductivity, sigma0ion, surface exchange coefficient, k, and the exponent n in Cv=C0v•a(O2)n.), are developed. Finally, sigma0ion and k are determined by fitting the oxygen permeation data to the two models using the exponent n determined by TG (n=-0.01). Oxygen permeation fluxes for Ba(Fe,Co,Zr)O3-delta membranes were measured as a function of temperature and oxygen activity on the sweep gas side. Thickness dependency of oxygen permeation (ag1=0.21 and ag2=0.02) shows clearly that oxygen permeation in Ba(Fe,Co,Zr)O3-delta membranes is partially controlled by surface exchange reaction. Using the exponent n (=-0.01) determined by TG, the remaining two parameters (sigma0ion, k) are determined by fitting the experimental data to the models. In terms of curvatures of flux lines calculated from both models, the second model seems to provide better description of oxygen permeation. However, there was no big difference in activation energies of sigma0ion and k, and the calculated characteristic length, Lc. When a new parameter, the dependency of surface exchange coefficient on oxygen activity (k=k0•ag(O2)m or k=k0•as(O2)m) is introduced to both models, reasonable values for sigma0ion, k, and m as well as higher fitting quality can be obtained. For both cases, the dependency of surface exchange coefficient on oxygen activity (m=0.80 for the first model and m=0.40 for the second model in k=k0•ag(O2)m), and m=1.55 for the first model and m=0.80 for the second model in k=k0•as(O2)m) is scattered roughly in the same range of the literature data (m=0.4~1.2). Oxygen permeation rates for fibre type membrane (wall thickness 0.16 mm) are measured as a function of temperature and sweep gas flow rate (Ar flow rate). Using a simple Wagner equation, overall activation energy of oxygen transport across a fibre type Ba(Fe,Co,Zr)O3-delta membrane is evaluated, which lies between two activation energies obtained for disc type membrane. This confirms that very reasonable values for sigma0ion and k were obtained for disc type membrane. More quantitatively, the oxygen permeation rates of a fibre type membrane are calculated using the parameters obtained from disc type membrane. The calculated oxygen permeation rates of a fibre type membrane do not deviate so much from the experimental data. The calculation results show further that the presence of bubbles (or pores) can reduce the oxygen permeation rates of fibre type membrane and the total oxygen permeation rates of fibre type membrane are higher in counter-current that in co-current. Overlap of TG relaxation curves of 0.42 mm thick membrane with that of 0.13 mm thick membrane means that intrinsic relaxation induced by Dchem and kchem is so fast and the response of TG furnace is so slow that it is impossible to discern TG relaxation curves of two membranes from the response of TG furnace. Comparison of the response of TG furnace (directly measured by oxygen sensor) with the relaxation curve of two membranes strongly shows that the relaxation is controlled entirely by the response of TG furnace. In this case, the only minimum Dchem and kchem can be estimated by assuming a certain error boundary (xi) of the response of TG furnace. A parametric study shows that Dchem and kchem determined from single relaxation curve might include high errors. This provides two requirements for extraction of accurate Dchem and kchem: at least two relaxation curves should be obtained from two membranes and they should belong to different L/Lc regime."]},{"key":"dc:source","label":"Dc Source","values":["Aachen : Publikationsserver der RWTH Aachen University II, 126 S. Ill., graph. Darst. (2008). = Aachen, Techn. Hochsch., Diss., 2008"]},{"key":"dc:title","label":"Title","values":["Oxygen transport in Ba(Fe,Co,Zr)O 3 - delta membranes"]}]}],"canonical_facts":{"dc:contributor":["Schroeder, Michael"],"dc:coverage":["DE"],"dc:creator":["Byun, Young Chang"],"dc:date":["2008"],"dc:description":["The nonstoichiometry of Ba(Fe,Co,Zr)O3-delta (Zr-lean Ba(Fe,Co,Zr)O3-delta) is measured as a function of temperature and oxygen activity by TG. Very high nonstoichiometry (delta0=0.78 at a(O2)=1) is determined at 1273 K. From the nonstoichiometry of Ba(Fe,Co,Zr)O3-delta;, exponent n (n=-0.01) in Cv=C0v•a(O2)n, thermodynamic factor (gamma=140) and activation energy for oxygen vacancy formation (DeltaEf=1.5 kJ/mol) are estimated. Two oxygen transport models in Ba(Fe,Co,Zr)O3-delta membranes are proposed. In bulk, oxygen ion diffusion is described by the classical Wagner equation. At gas-solid interfaces, two models (two surface exchange reaction rates) are derived based on various surface exchange reaction kinetics. By combining two (oxygen ion diffusion in bulk and exchange reaction at gas-solid interfaces), two oxygen transport models, which have three parameters (oxygen ionic conductivity, sigma0ion, surface exchange coefficient, k, and the exponent n in Cv=C0v•a(O2)n.), are developed. Finally, sigma0ion and k are determined by fitting the oxygen permeation data to the two models using the exponent n determined by TG (n=-0.01). Oxygen permeation fluxes for Ba(Fe,Co,Zr)O3-delta membranes were measured as a function of temperature and oxygen activity on the sweep gas side. Thickness dependency of oxygen permeation (ag1=0.21 and ag2=0.02) shows clearly that oxygen permeation in Ba(Fe,Co,Zr)O3-delta membranes is partially controlled by surface exchange reaction. Using the exponent n (=-0.01) determined by TG, the remaining two parameters (sigma0ion, k) are determined by fitting the experimental data to the models. In terms of curvatures of flux lines calculated from both models, the second model seems to provide better description of oxygen permeation. However, there was no big difference in activation energies of sigma0ion and k, and the calculated characteristic length, Lc. When a new parameter, the dependency of surface exchange coefficient on oxygen activity (k=k0•ag(O2)m or k=k0•as(O2)m) is introduced to both models, reasonable values for sigma0ion, k, and m as well as higher fitting quality can be obtained. For both cases, the dependency of surface exchange coefficient on oxygen activity (m=0.80 for the first model and m=0.40 for the second model in k=k0•ag(O2)m), and m=1.55 for the first model and m=0.80 for the second model in k=k0•as(O2)m) is scattered roughly in the same range of the literature data (m=0.4~1.2). Oxygen permeation rates for fibre type membrane (wall thickness 0.16 mm) are measured as a function of temperature and sweep gas flow rate (Ar flow rate). Using a simple Wagner equation, overall activation energy of oxygen transport across a fibre type Ba(Fe,Co,Zr)O3-delta membrane is evaluated, which lies between two activation energies obtained for disc type membrane. This confirms that very reasonable values for sigma0ion and k were obtained for disc type membrane. More quantitatively, the oxygen permeation rates of a fibre type membrane are calculated using the parameters obtained from disc type membrane. The calculated oxygen permeation rates of a fibre type membrane do not deviate so much from the experimental data. The calculation results show further that the presence of bubbles (or pores) can reduce the oxygen permeation rates of fibre type membrane and the total oxygen permeation rates of fibre type membrane are higher in counter-current that in co-current. Overlap of TG relaxation curves of 0.42 mm thick membrane with that of 0.13 mm thick membrane means that intrinsic relaxation induced by Dchem and kchem is so fast and the response of TG furnace is so slow that it is impossible to discern TG relaxation curves of two membranes from the response of TG furnace. Comparison of the response of TG furnace (directly measured by oxygen sensor) with the relaxation curve of two membranes strongly shows that the relaxation is controlled entirely by the response of TG furnace. In this case, the only minimum Dchem and kchem can be estimated by assuming a certain error boundary (xi) of the response of TG furnace. A parametric study shows that Dchem and kchem determined from single relaxation curve might include high errors. This provides two requirements for extraction of accurate Dchem and kchem: at least two relaxation curves should be obtained from two membranes and they should belong to different L/Lc regime."],"dc:identifier":["https://publications.rwth-aachen.de/record/50579","https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-113119%22"],"dc:language":["eng"],"dc:publisher":["Publikationsserver der RWTH Aachen University"],"dc:relation":["info:eu-repo/semantics/altIdentifier/urn/urn:nbn:de:hbz:82-opus-26694"],"dc:rights":["info:eu-repo/semantics/openAccess"],"dc:source":["Aachen : Publikationsserver der RWTH Aachen University II, 126 S. Ill., graph. Darst. (2008). = Aachen, Techn. Hochsch., Diss., 2008"],"dc:subject":["info:eu-repo/classification/ddc/540","Membran","Sauerstofftransport","Chemie","Sauerstofftrennung","oxygen separation","membrane"],"dc:title":["Oxygen transport in Ba(Fe,Co,Zr)O 3 - delta membranes"],"dc:type":["info:eu-repo/semantics/doctoralThesis","info:eu-repo/semantics/publishedVersion"]},"updated_at":"2026-07-30T19:40:25Z"}