Papers by Author: Célia Fraga Malfatti

Abstract: Plasma sprayed alumina coating is applied in many industrial applications in order to promote wear and corrosion resistance. Nonetheless, high porosity remained after deposition is a critical factor because it decreases the wear resistance. Some inorganic sealants can be used to reduce the open pores and superficial micro-cracks effect, improving the wear and corrosion resistance of alumina coatings. In this work, plasma sprayed alumina coating samples were divided into two groups: i) impregnated with inorganic sealant (AlPO4) and heat treated; ii) as deposited. Erosive wear tests were carried out in an erosion rig according to ASTM G76. The samples were subjected to an erodent flux, with impact angles of 30º up to 90º, at a velocity of 50m/s and temperatures of 25°C up to 400°C. The samples were characterized by SEM, Vickers microhardness, potentiodynamic anodic polarization and erosive wear rate. Results showed that erosive wear rate of alumina impregnated coating is lower than without the sealant. The sealed alumina coating presented higher mechanical properties; improved microstructural characteristics and the sealant promoted better lamellae contact, as can be observed by less sharpness in pits formation of microstructure.

Abstract: The development of solid oxide fuel cell has shown that the thin film concept for the electrode supported designs, based on the yttria-stabilized zirconia, is more promising than the research of new electrolyte materials. In this work, the spray pyrolysis process was investigated in order to obtain dense thin films of YSZ on porous ceramic substrates. High porosity LSM, a typical material of SOFC cathodes, was used as substrate. The precursor solution was obtained by zirconium and yttrium salts dissolved in a mixture of ethanol and propylene glycol, with volume ratio 1:1. The substrate was heated and maintained at a constant temperature (280°C, 340°C or 560°C). The as-obtained films were heat treated in a temperature of 700°C, aiming to obtain yttria-stabilized-zirconia films from the amorphous film. The morphology and microstructure of the films were characterized by scanning electron microscopy and X-ray diffraction.

Abstract: The sol-gel process based on silanes precursors appeared in recent years as a strong alternative for post-treatment to provide an optimization of the protective efficacy of zinc. Moreover, this process has been used to replace chemical chromating conversion based on hexavalent chromium. The silane films are hybrid compounds that provide characteristics of both polymeric materials, such as flexibility and functional compatibility, and ceramic materials, such as high strength and durability. The present work aimed to evaluate the influence of silane films obtained by dip-coating, on the characteristics of electrodeposited zinc coatings. The xerogel films showed a homogeneous surface and a better performance on the corrosion resistance than zinc coating without post-treatment, what can be confirmed by the electrochemical impedance results. These tests showed that application of the silane film promotes the occurrence of one more time constant compared to pure zinc system, hindering the corrosion process.