Anodic Oxidation of Porous Aluminium Pellets

The anodization of porous aluminum pellets is accompanied by a change in the composition of the electrolyte within the pellet pores. This change can be accounted for by electrochemical transport of ions to the electrodes and the inability of the system to overcome the concentrating effects in the anolyte. It is shown that this effect can, depending on the composition of the bulk electrolyte, result in a strong acid environment or a weakly conducting electrolyte within the pellet. Either condition results in undesirable oxidizing characteristics; a strong acid will lead to the formation of a porous film which is poorly impregnated by the solid electrolyte, and the resistive electrolyte impedes the growth of oxide film. This work indicates that these extreme conditions may be avoided by the use of electrolytes containing salts of organic acids of moderate strength.