To understand the role of water on zirconium passivation in n-butanol solutions containing Bun4NBr, composition and corrosion properties of the passive film were studied using cyclic voltammetry, X-ray photoelectron and electrochemical impedance spectroscopy. Zirconium undergoes spontaneous passivation followed by pitting corrosion as a result of passivity breakdown by the aggressive attack of bromide anions. The passive film consists mainly of ZrO2, ZrO2·2H2O and a small amount of zirconium butoxide. The pitting potential shifts positively and pitting corrosion is seriously inhibited with the addition of a small amount of water. Water improves the pitting corrosion resistance of the passive film by changing the thickness and the relative ratio of OH−/O2−. The result is helpful to electrosynthesize zirconium butoxide with high energy efficiency.
CeO 2 was used as the only oxidant for aniline polymerization, and polyaniline (PANI) was grown on CeO 2 surface to form CeO 2 @PANI nanocomposites. SEM and TEM showed that the CeO 2 @PANI composites were nanorods in a core-shell structure. XPS indicated that CeO 2 -core was reduced by aniline into Ce 3+ , which was then captured by the PANI-shell. Then the passive ability of CeO 2 @PANI coating on steels was explored. EIS showed that the impedance modulus of the CeO 2 @PANI coating exceeded 10 8 Ω·cm 2 after accelerated immersion. The SVET and XPS confirmed that PANI polarized the anodic reaction, Ce 3+ suppressed the cathodic reaction, and PO 4 3− formed complex precipitation. Some high-valent metal oxides can directly oxidize the aniline polymerization to form MO@PANI hybrid particles. The cations obtained by the metal oxide reduction can be captured by PANI and participate in passivation together with dopants. This study provides a new kind of nanocomposite fillers that can effectively passivate steel substrates within epoxy coatings for long-time protection.
The influence of humic acid-mediated extracellular electron transfer (EET) of Shewanella putrefaciens CN32 in microbiologically influenced corrosion (MIC) on 304 stainless steel was investigated. Humic acid plays a key role in accelerating passive film degradation in the presence of S. putrefaciens CN32, with a concentration-dependent effect; but has no effect when alone. It facilitated the formation of larger biofilm and increased Fe and Cr dissolution, resulting in a thinner, weakened passive film and intensified pitting corrosion. In-situ scanning electrochemical microscopy demonstrated S. putrefaciens CN32 utilized humic acid to perform outward EET, injecting electrons into the passive film and accelerating MIC.
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