Investigation under conditions of accelerated anodic corrosion of the effect of TiO2 substitution by CeO2 on the stability of Ir-based ceramic coatings

Ti-supported electrodes of nominal composition Ti/Ir0.3Ti(0.7-x)CexO2 (0 less than or equal to x less than or equal to 0.7) were prepared by thermal decomposition of the chloride precursor mixtures (450 degrees C). A systematic study of the corrosion behaviour of these anodes was performed under conditions of accelerated corrosion (j=800 mA cm(-2)) in acidic medium. The service life, SL, strongly depended on electrode composition, varying between 6 and 47 h, CeO2 introduction producing more unstable materials. Anodes containing 30 less than or equal to mol% CeO2 less than or equal to 60 present the lowest SL. This finding is possibly related to the preferential dissolution of Ce in association with the crystalline structure of these coatings (amorphous phase or low degree of crystallinity). The highest SL was observed for the Ti/Ir0.3Ti0.7O2 composition, probably as a result of the formation of a solid solution between Ir and Ti, besides a more compact oxide layer, which delays the Ti-o support passivation. A mixed mechanism of anode deactivation is operative. Complementar analyses, such as ICPES, EDX, SEM and CV, allowed to verify that passivation is the main source of the Ti/Ir0.3Ti0.7O2 deactivation, while coating consumption is the main factor responsible for deactivation of high CeO2 containing anodes.