Duplex coating consisting of an inner cerium-based layer and polypyrrole (PPy) film topcoat was electrodeposited onto AISI 304 stainless steel. The cerium-based coating was electrodeposited in solutions containing cerium nitrate at 50 ºC. The polymeric outer layer was electropolymerized in the presence of sodium bis(2-ethylhexyl) sulfosuccinate (AOT). The electrosynthesis was done under potentiostat conditions. The coatings were characterized by scanning electron microscopy (SEM) and energy dispersive x-ray spectrometry (EDX). The morphology of the double-layered cerium polypyrrole film shows a granular structure with the presence of agglomerates of small grains.
The anticorrosive performance of the coatings was evaluated in sodium chloride solution by linear polarization, open circuit measurements, and electrochemical impedance spectroscopy (EIS). Single films, cerium layer and PPy coating, and the duplex film all reduce the corrosion rate of AISI 304 stainless steel in NaCl solution. The duplex coating presents an improved corrosion resistance concerning the single films. The combination of the characteristics of the single layers is responsible for the superior corrosion protection efficiency of the double-layered cerium polypyrrole coating.
A duplex coating was formed under potentiostatic conditions on magnesium
alloy AZ91D in order to improve its corrosion resistance in simulated
physiological environment. The first layer was formed by anodization at low
potentials in molybdate solution. The outer layer was a PPy film
electro-synthesized in sodium salicylate solution. The conditions of the
formation were determined to obtain a layer with globular morphology. The
bilayer was characterized by scanning electron microscopy (SEM) and X-ray
diffraction (XRD). The corrosion protection properties of the coatings were
examined in Ringer solution by monitoring the open circuit potential (OCP),
polarization techniques, and electrochemical impedance spectroscopy (EIS).
The obtained results showed that the bilayer improves the corrosion
resistance of the substrate. Moreover, the duplex coating presented better
anticorrosive properties than the single PPy film. Afterwards, the bilayer
was modified by cementation of silver ions from a solution containing AgNO3.
The modified electrode exhibited good antibacterial properties.
RESUMEN Debido a su biocompatibilidad, biodegradabilidad y características mecánicas similares a las del hueso humano, las aleaciones de Mg constituyen una alternativa prometedora como materiales para la fabricación de implantes temporales. Sin embargo, su alta velocidad de degradación en ambiente fisiológico es un impedimento para estas aplicaciones. Con la finalidad de incrementar la resistencia a la corrosión de la aleación de Mg AZ91D en ambiente fisiológico simulado, se generaron recubrimientos dobles de cerio y epoxi modificados. Como primer paso se sintetizó químicamente polipirrol (PPy) modificado con nanopartículas de plata a partir de pirrol (Py), AgNO3 y Ce(SO4)2. Se sintetizaron dos tamaños de nanopartículas variando la concentración de AgNO3 empleada para la síntesis de los polvos. Se verificó que los compuestos tienen propiedades bactericidas contra la bacteria Gram negativa Escherichia cole (E. cori). A partir de estos resultados, se formó un recubrimiento doble sobre la aleación y éste fue modificado con los polvos sintetizados. El recubrimiento consistió en una primera película base cerio y una segunda película epoxi, a la cual se le adicionó un 1% p/p de los compuestos bactericidas. Análisis electroquímicos como polarizaciones anódicas, curvas de polarización de Tafo, variación del potencial de circuito abierto (PCA) y espectroscopia de impedancia electroquímica (EIS) verificaron que los recubrimientos modificados fueron capaces de proteger al sustrato contra la corrosión en solución fisiológica simulada. A su vez, la adición del compuesto de PPy y plata confiere propiedades antibacteriales al recubrimiento, las cuales fueron evaluadas mediante la técnica de Kirby-Bauer contra la bacteria E. coli.
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