Corrosion Product and Inhibitor Films on Aluminum

McCune, H. W.

doi:10.1149/1.2427268

Cited by 3 publications

(2 citation statements)

References 3 publications

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“…The presence of metallic A1 was also previously found in the anodic flakes (6)(7)(8). However, nobody observed the v e r y fine particles (down to about 5 x 10 -5 m m in diameter) in the deposits, only occasional large chunks and the cubes as found by Stretcher et al (9).…”

Section: Discussionsupporting

confidence: 69%

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The Valency of Aluminum Ions and the Anodic Disintegration of the Metal

Straumanis¹,

Poush²

1965

J. Electrochem. Soc.

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It appears from coulometric measurements that Al in Al‐amalgam may go into solution in basic electrolytes exclusively as a trivalent ion. Experiments made in aqueous solutions of normalNaOH , HNO3 , KNO3 , and K2Cr2O7 showed that at anodic current densities between 20 and 300 ma/cm2 dark, nearly black films, which constantly broke down, are formed on the Al electrode. Microscopic examinations revealed the presence of a multitude of metallic particles entangled in the hydrated Al‐oxide flakes, causing the dark color of the latter. Depending on the conditions, the diameter of the metallic particles and leaflets varied from almost 10−5 to 10−2 mm. Such a disintegration of Al was also observed when the partially amalgamated metal merely came in contact with distilled H2O : dark flakes of hydroxide, containing a multitude of smallest Al particles, were formed. There are indications that the disintegration of Al is caused by the forcible breakdown (e.g., by the current or Hg) of the oxide layers firmly sticking to the surface of the metal. On breaking down of the film the smallest Al particles which remain on the film are torn from the meal. The observed deviation from Faraday's law and the negative difference effect, may be explained in terms of this behavior, without recourse to the hypothesis of lower valency Al ions.

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Section: Discussionsupporting

confidence: 69%

“…Although he rejected the formation of A1 according to reaction [3], he did not mention anodic disintegration, which might well have provided an explanation. Aluminum in anodic deposits and films was also found by McCune (7) and Dmitriev etal. (8).…”

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confidence: 74%

The Valency of Aluminum Ions and the Anodic Disintegration of the Metal

Straumanis¹,

Poush²

1965

J. Electrochem. Soc.

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Anodic Dissolution of Metals—Anomalous Valence

James

1974

Advances in Corrosion Science and Technology

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INTRODUCTIONWhen metals are dissolved anodically in aqueous and nonaqueous media, the weight of metal dissolved is sometimes greater than that calculated from Faraday's law assuming normal oxidation states. Among several metals of industrial importance, AI, Be, Cd, Fe, Pb, Mg, Ti, and Zn exhibit this phenomenon. The usual implication is that these metals dissolve as ions with an ionic valence or oxidation number less than normal, e.g., Mg+, Be+, etc.Actually, anomalous anodic dissolution, i.e., that which results in a weight loss of an anode larger than that based on coulometric data, was first reported for Al over a century ago by its discoverers, Wohler and Buff. 1 Yet interestingly enough, despite the considerable research which has focused on this problem since that time, the exact nature of anomalous dissolution of metals remains in dispute.One mechanism which has received considerable support is the concept of univalent (unipositive) ion formation, sometimes referred to as the transitory ion mechanism.The unipositive (uncommon) ion mechanism has been especially espoused in large part by two major groups: Epelboin and co-workers at the University of Paris and Davidson, Kleinberg, and co-workers at the University of Kansas, Lawrence. The mechanism was first employed by Epelboin to explain the apparent valence of 1.40 for Zn dissolving anodically in aqueous perchlorate solution. 2 This value was obtained both from Straumanis, James, and co-workers at the University of MissouriRolla have attributed anomalous anodic dissolution of metals in aqueous solution, as have many other electrochemists, to the competition of secondary processes with an electrochemical oxidation step excluding that of transitory ion formation. They have explained the anomalous dissolution of many metals in aqueous media as arising from related phenomena: local action, film-controlled polarization, and anodic disintegration. The reader should be made aware that these phenomena often involve, but are not necessarily confined to, secondary processes frequently encountered in the electrochemistry of metals dissolving in dilute aqueous systems. Indeed, the major complaint of Epelboin is that too many electrochemists choose to confine their studies of anomalous anodic dissolution within the framework of classical electrochemistry. Despite the conflicting philosophies of the different approaches, considerable credit must be accorded to Epelboin and his colleagues in their extensive and well-planned efforts to come up with a universal and quantitative mechanism of anodic dissolution based on sound kinetic and thermodynamic principles.There is no argument that experimental and theoretical considerations of anomalous dissolution from existing and new points of view are essential to research and development with regard to corrosion protection and inhibition, batteries and other energy devices, electrochemical synthesis, and other associated electronic properties of interfaces. Accordingly, the following review is presented with the hope that it will ...

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