Effect of pH on Thickness and Ion Content of the Oxide Film on Aluminum in NaCl Media

Abstract

The effect of solution pH on some characteristic properties, i.e., thickness and ion content, of the surface oxide film on high purity aluminum exposed to NaCl solutions have been analyzed by X-ray photoelectron spectroscopy (XPS). The aluminum oxide film thickness is strongly dependent upon the solution pH. In the active dissolution range, i.e., pH <3 and >11, the oxide film is thinner than the native oxide film formed after polishing. Two local maxima were observed at pH ∼3.8 and ∼10.7 where the thickness of the film was 68 and 98 Å, respectively. We found only a slight thickness variation in the passive region of aluminum, 4<normalpH<10, which represented a film thickness of 40-45 Å. The comparison of the aluminum dissolution data with XPS results indicates that the oxide film is thicker at the limits of aluminum stability. The chloride content of the film maximized at pH ∼3.8 and exhibited a minimum at pH ∼10. The sodium concentration reached its maximum value at pH 11.6. Such a pH dependent ion concentration in the passive film is most likely the result of ion bonding to the OH-terminated surface and subsurface groups at the oxide film. © 2001 The Electrochemical Society. All rights reserved.

Chloride Ion Interactions with Oxide-Covered Aluminum Leading to Pitting Corrosion: A Review

“…Several authors 27,43,[56][57][58]63,67,71,75,76 found Cl − within the oxide film at potentials below E pit and others 46,47 have found Cl − within the oxide film at potentials above E pit . The modeling work by O'Grady et al 79 show Cl − within the oxide and at the oxide metal/interface at potentials below E pit .…”

“…103 This approach has been used in several studies. 43,67,76 The thickness of the air-formed oxide on Al using XPS was reported to be 4.8 nm by Strohmeier, 103 3.7 nm by Kolics et al 76 and 4.0 nm by Yu et al 67 These Figure 1. pH dependence of chloride adsorption on aluminum ( R is the surface concentration of the radioactive isotope) in 0.1 M NaClO 4 .…”

“…Prior to XPS analysis, the aluminum substrate was exposed to 0.1 M NaCl, pH 4.0 solution for 45 minutes. 76 Reproduced by permission of ECS-The Electrochemical Society.…”

Electrochemical noise and impedance study of aluminium in weakly acid chloride solution

“…Amongst these, some studies have been undertaken in weakly acid solution in order to throw light on the effect of pH on the rate of the corrosion process [1][2][3][4][5][6], its inhibition by the addition of organic compounds [7,8], the influence of metal ions [9][10][11] and on the structure of the oxide layer and its semiconductor properties [2]. Electrochemical techniques employed have been mainly open circuit potential (OCP) measurements, polarisation curves and electrochemical impedance.…”

“…Polarisation curves [2] and polarisation curves and impedance [3] were used to examine the corrosion behaviour in acetic acid/acetate solutions with a view to controlling the pH near the aluminium surface and gain insight into the corrosion mechanism. The study described in [4] used X-ray photoelectron spectroscopy (XPS) to investigate the influence of pH on the thickness and ion content of the aluminium oxide film in sodium chloride solution. Evidence was found for thicker oxide films at the extremes of oxide stability and the chloride content of the oxide film was maximum at pH 3.8.…”