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

Abstract

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 , , , and 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 : 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.