Electrochemical behaviour of some transition metal acetylacetonate complexes as corrosion inhibitors for mild steel

Corrosion inhibition of some metal acetylacetonate complexes including Co(acac)2, Cu(acac)2, Mn(acac)2 and Zn(acac)2 was evaluated using electrochemical impedance spectroscopy (EIS) in 3.5% NaCl for mild steel. The results were compared to zinc potassium chromate (ZPC) solution in 3.5% NaCl. Corrosion inhibition of these metal complexes followed the order: ZPC > Co(acac)2 > Zn(acac)2 > Mn(acac)2 while Cu(acac)2 displayed corrosion catalytic activity. Solutions containing metal acetylacetonate complexes had an increase in pH compared to Blank and ZPC solutions, which indicated partial dissociation of ligand and metallic cations. However, after 24-h contact with the mild steel samples the solutions pH were dropped which implied decrease of the complex concentration in the test solutions. SEM images showed no detectable deposited film on the surface exposed Co(acac)2 solution while EDX analysis revealed precipitation of a layer containing 4.14% Co. SEM-EDX results for samples immersed in Zn(acac)2 and Mn(acac)2 solution showed precipitation of Zn and Na components and Mn complex on the surface, respectively.