Síntese de manganita dopada com estrôncio e cobaltita dopada com antimônio e caracterização microestrutural

AUTOR(ES)
FONTE

IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia

DATA DE PUBLICAÇÃO

2012

RESUMO

The great variety of properties of oxides with the perovskite structure allows their application in several fields of technology. Specially, the electrochemical properties and the thermal stability of some of these compounds make these materials the most used in devices for energy generation such as the solid oxide fuel cells (SOFC). SOFC¿s are devices the reach high efficiencies in the conversion of electric energy and are likely to be used in sustainable and distributed energy generation. For this cells, perovskitas composed by strontium doped lanthanum manganites (LSM) is the material that fits most of requirements for the application in SOFC¿s cathodes. In the intermediate temperature solid oxide fuel cells (IT-SOFC) there is the possibility to build a cell with thin ceramic films supported in a metallic interconnector. However, for IT-SOFC¿s cathodes, LSM no longer has a good electrochemical performance due to the device¿s lower operating temperatures, being necessary the development of mixed conductors to increase the amount of reactive sites for the reduction of O2. In this context, the development of cathodes based on antimony doped strontium cobaltites (SCS) perovskites is being proposed to this application. This work was executed looking for the obtaining of LSM, a material for SOFC cathodes, and to evaluate its behavior against processing conditions; and for the obtaining of SCS, a material for IT-SOFC cathodes. LSM powders were obtained by combustion synthesis, varying the amount and type of fuel, and observing the resulting morphological aspect conferred by the selected parameters. For comparison, the obtaining of LSM powders was carried out via the sol-gel method. The combustion method was also used for the obtaining of SCS, watching for the calcination time. LSM powders were processed and powder with most promising characteristics was used in dispersions for dip coating of dense YSZ substrates. The LSM perovskite was obtained as a single phase powder after calcination without influence of the fuel excess, fuel type or synthesis method, in the final formation of the rhombohedral structure. Aggregates with distinct morphology, formed by nanocrystalline particles with average size around 30 nm, were observed when sucrose was used as fuel and also when mixed with urea in the precursor solution, which formed crystallites with average size near 20 nm. The use of sucrose also promoted the obtaining of the powder with the higher specific surface area (34,9 m²/g) which presented sintering rates higher than the other powders. When not too rough, the YSZ substrates had more continuous films formed in its surface and also when the first depositions were made with the substrates slowly emerging from the bath. The use of a solution based on distilled water with higher amount of binder, promoted the obtaining of films as thin as 3 ¿m and with a porous microstructure. Combustion synthesis also led to the obtaining of the SCS perovskite, however after 6 hours calcination the powder still presented secondary phases and longer calcination periods may be necessary for the obtaining of a single phase material. The high heat of the SCS synthesis reaction formed dense, yet nanocrystalline aggregates.

ASSUNTO(S)

sinterização lsm células a combustível scs filmes finos perovskite cathode dip coating sol-gel materiais cerâmicos : ensaios sofc it-sofc combustion synthesis

ACESSO AO ARTIGO

Documentos Relacionados