Influence of synthetic method on the properties of La0.5Ba0.5FeO3 SOFC cathode

Power Point presentado en The Energy and Materials Research Conference - EMR2015 celebrado en Madrid (España) entre el 25-27 de febrero de 2015Perovskite type (ABO3) oxides have been widely studied as SOFC cathode materials at high temperatures. Given that several of the challenges hindering SOFC technology are consequence of the high operation temperature (about 1000ºC) [1,2], an important goal is to reduce it to 600-800ºC. To minimize this effect new perovskite-type mixed ionic-electronic conducting oxides have been widely studied as promising IT-SOFC cathodes. Among them, iron perovskites (LSF) seem to be good candidates mainly for their appropriate thermal expansion match with YSZ electrolytes and their good catalytic activity for the oxygen reduction [3,4]. The properties of these compounds and thus their cell performance depends on several factors: the right choice of A and B elements, the amount of doping cations (A1-xAx) and some structural parameters such as the tolerance factor [5], the average size of the A-site cations () and the A cation size disorder (σ2(rA)). Studies on the influence of the hole-doping (x) in the A-site of LSF perovskites have shown good cathode performances in compounds with intermediate doping levels [6]. The change of and σ2(rA) indicate that better performances are observed for highest and lowest σ2(rA) [7]. External parameters, such as the synthetic method, are also important factors that influence the final properties [8]. In this sense it has been observed that porosity, grain size and morphology of the compounds strongly depend on the sample preparation techniques. In this research, a La0.5Ba0.5FeO3 perovskite has been synthesized by two different methods (ceramic and glycine-nitrate routes) in order to study the synthetic method influence on the properties of this compound as IT-SOFC cathode material. This composition has been chosen due to its intermediate hole doping level (0.5) and high average size of the A-site cations ( = 1.48 Å, when rA are standard 12-coordinate ionic radii), these parameters, according with previous studies should show interesting properties for its use as SOFC cathode. It has been observed that the two La0.5Ba0.5FeO3 compounds show different room temperature crystal structure depending on the synthesis route. The sample obtained by the ceramic method has higher oxygen vacancy content, but in the other hand the SEM micrographs show that glycine-nitrate process leads to a compound with porous structure and particles with nanometric grain sizes. At 700 or 800ºC the electrical conductivity of both samples is similar but the sample obtained by glycine-nitrate route shows better electrochemical performance. The ceramic sample has lower adherence than the glycine counterpart and this derivates in higher values of polarization resistance. It is believed that this is a consequence of the heterogenous morphology of this sample. Therefore, it seems that the glycine-nitrate synthetic method is a more appropriate technique for preparing perovskite cathodes

Polyacrylamide Ferrogels with Magnetite or Strontium Hexaferrite: Next Step in the Development of Soft Biomimetic Matter for Biosensor Applications

Magnetic biosensors are an important part of biomedical applications of magnetic materials. As the living tissue is basically a " soft matter." this study addresses the development of ferrogels (FG) with micron sized magnetic particles of magnetite and strontium hexaferrite mimicking the living tissue. The basic composition of the FG comprised the polymeric network of polyacrylamide, synthesized by free radical polymerization of monomeric acrylamide (AAm) in water solution at three levels of concentration (1.1 M, 0.85 M and 0.58 M) to provide the FG with varying elasticity. To improve FG biocompatibility and to prevent the precipitation of the particles, polysaccharide thickeners-guar gum or xanthan gum were used. The content of magnetic particles in FG varied up to 5.2 wt % depending on the FG composition. The mechanical properties of FG and their deformation in a uniform magnetic field were comparatively analyzed. FG filled with strontium hexaferrite particles have larger Young's modulus value than FG filled with magnetite particles, most likely due to the specific features of the adhesion of the network's polymeric subchains on the surface of the particles. FG networks with xanthan are stronger and have higher modulus than the FG with guar. FG based on magnetite, contract in a magnetic field 0.42 T, whereas some FG based on strontium hexaferrite swell. Weak FG with the lowest concentration of AAm shows a much stronger response to a field, as the concentration of AAm governs the Young's modulus of ferrogel. A small magnetic field magnetoimpedance sensor prototype with Co68.6Fe3.9Mo3.0Si12.0B12.5 rapidly quenched amorphous ribbon based element was designed aiming to develop a sensor working with a disposable stripe sensitive element. The proposed protocol allowed measurements of the concentration dependence of magnetic particles in gels using magnetoimpedance responses in the presence of magnetite and strontium hexaferrite ferrogels with xanthan. We have discussed the importance of magnetic history for the detection process and demonstrated the importance of remnant magnetization in the case of the gels with large magnetic particles.This work was supported in part within the framework of the state task of the Ministry of Education and Science of Russia 3.6121.2017/8.9; RFBR grant 16-08-00609 and by the ACTIMAT grant of the Basque Country Government. Selected studies were made at SGIKER Common Services of UPV-EHU and URFU Common Services. We thank I.V. Beketov, A.A. Svalova, Burgoa Beitia, A. Amirabadizadeh, A. Garcia-Arribas and I. Orue for their special support

Mechanical Force Acting on Ferrogel in a Non-Uniform Magnetic Field: Measurements and Modeling

The development of magnetoactive microsystems for targeted drug delivery, magnetic biodetection, and replacement therapy is an important task of present day biomedical research. In this work, we experimentally studied the mechanical force acting in cylindrical ferrogel samples due to the application of a non-uniform magnetic field. A commercial microsystem is not available for this type of experimental study. Therefore, the original experimental setup for measuring the mechanical force on ferrogel in a non-uniform magnetic field was designed, calibrated, and tested. An external magnetic field was provided by an electromagnet. The maximum intensity at the surface of the electromagnet was 39.8 kA/m and it linearly decreased within 10 mm distance from the magnet. The Ferrogel samples were based on a double networking polymeric structure which included a chemical network of polyacrylamide and a physical network of natural polysaccharide guar. Magnetite particles, 0.25 micron in diameter, were embedded in the hydrogel structure, up to 24% by weight. The forces of attraction between an electromagnet and cylindrical ferrogel samples, 9 mm in height and 13 mm in diameter, increased with field intensity and the concentration of magnetic particles, and varied within 0.1–30 mN. The model provided a fair evaluation of the mechanical forces that emerged in ferrogel samples placed in a non-uniform magnetic field and proved to be useful for predicting the deformation of ferrogels in practical bioengineering applications. © 2022 by the authors.Ministry of Education and Science of the Russian Federation, Minobrnauka: FEUZ-2020-0051; Russian Science Foundation, RSF: 20-12-00031; Ministry of Health of the Russian Federation: 121032300335-1This study was in part supported by the program of the Ministry of Health of the Russian Federation (project 121032300335-1). A.Yu. Zubarev and A.P. Safronov acknowledge the financial support of the Russian Science Foundation for theoretical modeling and the numerical verification of the model (grant 20-12-00031). This work was in part financially supported by (G.V. Kurlyandskaya and G.Yu. Melnikov) the Ministry of Science and Higher Education of the Russian Federation (grant number FEUZ-2020-0051)

Influence of synthetic method on the properties of La0.5Ba0.5FeO3 SOFC cathode

Power Point presentado en The Energy and Materials Research Conference - EMR2015 celebrado en Madrid (España) entre el 25-27 de febrero de 2015Perovskite type (ABO3) oxides have been widely studied as SOFC cathode materials at high temperatures. Given that several of the challenges hindering SOFC technology are consequence of the high operation temperature (about 1000ºC) [1,2], an important goal is to reduce it to 600-800ºC. To minimize this effect new perovskite-type mixed ionic-electronic conducting oxides have been widely studied as promising IT-SOFC cathodes. Among them, iron perovskites (LSF) seem to be good candidates mainly for their appropriate thermal expansion match with YSZ electrolytes and their good catalytic activity for the oxygen reduction [3,4]. The properties of these compounds and thus their cell performance depends on several factors: the right choice of A and B elements, the amount of doping cations (A1-xAx) and some structural parameters such as the tolerance factor [5], the average size of the A-site cations () and the A cation size disorder (σ2(rA)). Studies on the influence of the hole-doping (x) in the A-site of LSF perovskites have shown good cathode performances in compounds with intermediate doping levels [6]. The change of and σ2(rA) indicate that better performances are observed for highest and lowest σ2(rA) [7]. External parameters, such as the synthetic method, are also important factors that influence the final properties [8]. In this sense it has been observed that porosity, grain size and morphology of the compounds strongly depend on the sample preparation techniques. In this research, a La0.5Ba0.5FeO3 perovskite has been synthesized by two different methods (ceramic and glycine-nitrate routes) in order to study the synthetic method influence on the properties of this compound as IT-SOFC cathode material. This composition has been chosen due to its intermediate hole doping level (0.5) and high average size of the A-site cations ( = 1.48 Å, when rA are standard 12-coordinate ionic radii), these parameters, according with previous studies should show interesting properties for its use as SOFC cathode. It has been observed that the two La0.5Ba0.5FeO3 compounds show different room temperature crystal structure depending on the synthesis route. The sample obtained by the ceramic method has higher oxygen vacancy content, but in the other hand the SEM micrographs show that glycine-nitrate process leads to a compound with porous structure and particles with nanometric grain sizes. At 700 or 800ºC the electrical conductivity of both samples is similar but the sample obtained by glycine-nitrate route shows better electrochemical performance. The ceramic sample has lower adherence than the glycine counterpart and this derivates in higher values of polarization resistance. It is believed that this is a consequence of the heterogenous morphology of this sample. Therefore, it seems that the glycine-nitrate synthetic method is a more appropriate technique for preparing perovskite cathodes