Sorption of Sulfate and Chloride Anions on a Well-Characterized Al 2024 Electrode

Abstract

We studied sorption processes, adsorption and incorporation, of sulfate and chloride anions on the surface of well-characterized aluminum 2024 alloy using electrochemical, radiochemical, and ultrahigh-vacuum spectroscopic techniques. The measurements were carried out at an open-circuit potential and in the electrode potential range on the negative side of the open-circuit potential (cathodic polarization conditions), at various pH values. The focus was on sorption reversibility as well as on the relationship between anion's surface concentration and the electrode potential. We have found that sorption of sulfate anion is controlled by pH, surface charge, and the stability of aluminum oxide films. We have also found that adsorption of chloride is weaker than sulfate and is more irreversible since chloride incorporation occurs more readily than sulfate. The change in the alloy surface composition and morphology induced by the electrochemical treatment and anion adsorption was monitored by scanning Auger microscopy and energy-dispersive X-ray spectroscopy. The characterization exhibits copper-rich intrusions and extrusions that may act as either local cathodes or anodes in the overall alloy dissolution process. The distribution and evolution of such Cu-rich inclusions under studied experimental conditions were monitored and are reported. The dissolution of aluminum from the alloy affects both sulfate and chloride adsorption/incorporation processes. While sulfate and chloride adsorption have no effect on cathodic current measured in the studied electrode potential range, the high anion surface concentration may have a detrimental effect on the alloy stability, particularly when the beneficial influence of the cathodic polarization (protection) ends.

Inhibition by CO of the corrosion of Fe, Ni, and their alloys in concentrated HCl solutions

“…The interest in CO adsorption is mainly due to the detrimental role of adsorbed carbon monoxide in electrocatalysis, where it often acts as a poisoning intermediate that blocks active surface sites. This blocking effect, however, can be positive in other cases, for example in corrosion, a field that has also attracted Wieckowski's attention [8][9][10][11][12][13][14].…”

A closer look at the internal corrosion test for automotive heat exchangers: the OY water test

“…This does not seem to be the case in the OY water environment. Studies were carried out on pure aluminum and 2024 alloy showing the influence of sulfates and chlorides in sulfate, perchlorate or phosphate supported solutions 7, 13–16. It was revealed that SO 4 2− ions delay pit initiation by competitive adsorption with Cl − ions but accelerate the growth of pre‐existing pits.…”

First Principles, Explicit Interface Studies of Oxygen Vacancy and Chloride in Alumina Films for Corrosion Applications

“…[51][52][53][54] Computationally, fluorination of AlOH groups using HF gas has been predicted to be energetically favorable. [62][63][64] In this work, we report DFT energetics associated with Cl − →OH − on the α-Al 2 O 3 (0001) surface using parameters consistent with those we apply to examine Cl − insertion into V O inside the oxide film, so that a comparison of mechanisms can be made. The passivating alumina films on Al metal surfaces are known to be amorphous.…”