, Volume 17, Issue 2, pp 497-509
Date: 16 Nov 2012

Corrosion protective ability of electrodeposited ceria layers

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It has been ascertained that the electrochemically deposited thin films of cerium oxides, containing mainly CeO2 and also some insignificant amount of Ce2O3, are acting as an effective cathodic coating, leading to restoration of the passive state of the studied stainless steel (OC 404) samples. This effect is associated with a strong shifting of the stationary corrosion potential of the steel in positive direction, moving over from potentials characteristic of corrosion in active state to potentials falling within the zone of passivity. In this respect, another basic purpose of the investigations was the elucidation of the mechanism of action of the cerium oxide film and in particular collecting experimental evidence for the supposition about the occurrence of an efficient depolarization reaction of CeO2 reduction (resulting in a state of passivity—improved ability of self-passivation) instead of hydrogen depolarization reaction. For this purpose, we considered also the decrease in the surface concentration of ceria in the passive layer under the conditions of the actual corrosion process (self-dissolution) of the stainless steel by means of XPS, SEM, ICP-AES, and gravimetric analyses. A decrease in the surface concentration of CeO2 (Ce4+) has been observed, which is known to be chemically inert in acidic media. The obtained results prove the occurrence of an effective cathodic process of Ce4+ (CeO2) reduction into Ce3+ (soluble in acids Ce2O3 ) in the superficial oxide film.

This article is dedicated to Professor Alexander Milchev, honorary member of the Rostislaw Kaischew Institute of Physical Chemistry—Bulgarian Acadmy of Sciences, on the occasion of his 70th birthday.