Faradaic Reactions and Their Effects on Dissolution of the Natural Oxide Film on Pure Aluminum During Cathodic Polarization in Aqueous Solutions

Abstract

Faradaic reactions and their effects on dissolution of the natural oxide film on pure aluminum during cathodic polarization were investigated in aqueous 0.5 M sulfuric acid (H 2 SO 4 ) and 0.5 M sodium sulfate (Na 2 SO 4 ) solutions using the potentiodynamic polarization, rotating disk electrode (RDE), open-circuit potential (OCP) transient, and potentiostatic current transient methods. Potentiodynamic polarization curves for natural oxide-covered pure aluminum showed two Tafel slopes arising from the change in the faradaic reaction from oxygen reduction to water reduction with decreasing applied potential. The bare surface of pure aluminum was scarcely exposed to the electrolyte despite dissolution of the natural oxide film as a result of chemical attack by hydroxide ions during cathodic polarization. Chemical dissolution of the natural oxide film decreased the instantaneous value of OCP and was enhanced more by hydroxide ions resulting from water reduction than by hydroxide ions from oxygen reduction.

A microscopic study on the corrosion fatigue of ultra-fine grained and conventional Al–Mg alloy

“…Based on these results, in this study, the fine surface finish of 1200 grit would result in a higher density of cathodic intermetallic particles exposed at the surface, a lower surface rugosity and a higher susceptibility to localized corrosion. Similar results have been noted in other aluminum alloys such as AA 6061 and AA 7075 [32][33][34][35]. When large second phase inclusions were not present it appears the corrosion fatigue performance was determined by slip enhanced (anodic) dissolution around constituent particles as evidenced in the microstructure at high magnification ( Fig.…”

Using EIS to study the electrochemical response of alloy AA5083 in solutions of NaCl

“…Fig. In these, the initial value of the corrosion potential is determined in part by the ohmic drop caused by the natural film of oxide formed during the handling of the sample [33]. In this figure, it can be observed how, at the very beginning of the exposure period, the potential of the sample takes a value of around À 0.850 V and then evolves to reach a value close to À 0.740 Vafter 5 hours.…”

On the mixed nature of cerium conversion coatings

“…Fig. In this type of system, one of the factors determining the value of the initial corrosion potential is the ohmic fall caused by the natural film of oxide formed during the manipulation of the sample [27]. It can be observed in this figure how the value of the corrosion potential of the sample is of the order of À 0.850 V (Ag/AgCl) in the first moments of exposure.…”