Effect of sealing treatment on the corrosion resistance of thermal-sprayed ceramic coatings

Plasma-sprayed ceramic coatings usually are characterized by a relatively high open porosity, which is deleterious when these coatings have to perform in an aggressive environment. Various methods were applied to the as-deposited coatings in order to close this porosity and, hence, improve their corrosion resistance. In this study, plasma-sprayed alumina+titania coatings were sealed using different sealants such as phosphoric acid, phenol, and epoxy-based sealants. The effectiveness of the sealing treatment was determined through electrochemical testing, complemented by scanning electron microscopy (SEM) and optical microscopy observations. The results obtained indicated that both phenol and epoxy sealants resulted to be more effective than phosphoric acid in enhancing the corrosion resistance of thermally sprayed ceramic coatings used in the present research.