Adsorption of organic compounds at the aluminium oxide/aqueous solution interface during the aluminium anodizing process

The paper reports a systematic study concerning the role played by different organic compounds (glycolic acid, oxalic acid, glycerol) on the electrochemical oxidation process of aluminium in sulphuric acid solution. The result of the experiment as a whole provides a clear indication of the deep influence exerted by the three selected organic compounds on the aluminium oxide structure, leading to the formation of a more compact oxide layer. Electrochemical impedance spectroscopy results appear of particular interest; they are discussed in the light of a model proposed by Bojinov. The relevant parameters, half-jump distance a and cross-capture section S, are found consistently related to variations in the oxide structure (porosity). This gives a sounder basis to the physically correct nature of the assumptions underlying the Bojinov model, also suggesting that organic compounds are adsorbed at the aluminium oxide/aqueous solution interface.

Research highlights
► Glycolic acid, oxalic acid and glycerol are adsorbed at the oxide/solution interface of aluminium during anodizing.
► Adsorption of glycolic acid, oxalic acid and glycerol at the oxide/solution interface influence the structure of the oxide film.
► A less porous oxide structure is obtained when glycolic acid, oxalic acid and glycerol are present in solution.