PITTING DURING INITIATION OF SPARK ELECTRIC BREAKDOWN IN THE PROCESS OF ALUMINUM ANODIZATION IN NONAQUEOUS SOLUTIONS OF TRIALKYLAMMONIUM ALKYLCARBOXYLATES

Anodic activation of aluminium is studied in nonaqueous solutions (with dimethylformamide and butyrolactone as solvents) of methyl- and tributylammonium maleate and sebacate initiating spark electric breakdown during anodization. Anodic activation is shown to be caused by local rupture of passivity and pitting dissolution of the oxidized metal. Carboxylate anions are established as pitting activators in anodization. The nature of the induction period of pitting in anodization is discussed. Based on the results of measurements of the oxide's structure-sensitive properties by means of impedance, photoelectron spectroscopy, and others, the change of the oxide is demonstrated terminating in the pre-breakdown potential domain with the phase transition. Based on photo-emf, electrical conductivity, and capacity measurements, this change of the oxide during anodization is claimed to be caused by codeposition of anions in the oxide giving rise to electron donor type impurity point defects. A mechanism of pitting initiation during anodization is proposed taking into account the role of the impurity point defects in the oxide.