Abstract
The reaction between anodic aluminum oxide and several passivating solutions of citric acid and ammonium dihydrogen phosphate (ADP) is studied by capacitance measurements. In addition, the passivating effect of the above solutions has been evaluated by the reaction of the oxide with pure boiling water and subsequent anodization. The results show a strong passivating effect of the ADP solution which is partially diminished by the addition of citrate ions.