Influência do tamanho de grão da zircônia estabilizada com ítria e das propriedades reológicas de barbotinas anódicas sobre as características microestruturais de filmes de anodo usados em pilhas a combustível de óxidos sólidos.

Abstract

Solid oxide fuel cells (SOFCs) are devices capable of cleanly converting chemical energy into electric energy with a high efficiency. One of the most important components of SOFCs is the anode. Oxidative electrochemical reactions of the fuel gas occur in this electrode and the resulting electrons are transported to the cell interconnectors. Currently, NiO/YSZ composite is the most used material in the fabrication of anode films due mainly to its low cost. In this work, it was synthesized two YSZ powders (YSZ800 and YSZ1000) by the co-precipitation method. Two compounds NiO/YSZ (NiO/YSZ800 and NiO/YSZ1000) were prepared from these powders by impregnation. The NiO/YSZ powders were used to prepare eight ceramic slurries, which were later mixed for 5, 10, 20 and 40 h. These ceramic slurries were deposited by aerography onto the YSZ substrates, which were thermally treated later to form the anode film. Several techniques were used to characterize the YSZ powders and their composites. X-ray diffraction (XRD) was used to determine the crystalline phases present, possible amorphous phases, and crystallite size. The Brunauer, Emmett and Teller (BET) method helped in the determination of the specific surface area (ABET), total pore volume (Vt), and average pore diameter (dp) of YSZ800 and YSZ1000. The average particle size of these powders was calculated from the specific surface area given by BET. The rheological behavior of the ceramic slurries was studied with a rheometer. It showed that mixture time and YSZ powder grain size affect suspension viscosity significantly. The thermal properties of the ceramic slurries were evaluated by Thermal Analysis (TG) and Differential Thermal Analysis (DTA). Optical microscopy (OM) and Scanning Electron Microscopy (SEM) were used in the study of the film microstructure. From SEM images, it was possible to determine the porosity and pore contiguity, and YSZ and NiO contents. Energy-Dispersive Spectrometry (EDS) and Wavelength Dispersion System (WDS) analyses were used to detect the possible impurities present in the films and allowed the separate detection of yttrium and zirconium. The elemental map was used to verify the distribution of elements Y, Z, and Ni in films and to relate it to the ceramic slurries mixing time.