Molybdate and vanadate ions as corrosion inhibitors for clad aluminium alloy 2024-T3

• The effect of molybdate and vanadate as corrosion inhibitors for clad AA2024-T3 was investigated. • The inhibition degree by vanadate is linear in the concentration range from 0.5 mM to 250 mM. • The inhibition degree of molybdate is similar to vanadate for c ≤ 50 mM. • For c > 50, the inhibition effect of molybdate strongly increases shifting E br for 400 mV more positive. • The morphology and thickness of inhibitor layers on clad AA2024-T3 strongly differ for molybdate and vanadate. Molybdate and vanadate ions were used as corrosion inhibitors for the clad aluminium alloy 2024-T3 in chloride solution to investigate the differences in their inhibitory effect. Electrochemical measurements in 0.1 M NaCl investigated the influence of inhibitor concentration from 0.5 mM to 250 mM, solution pH from 5 to 9 and immersion time at open circuit potential of up to 12 h. Both compounds act predominantly as anodic inhibitors; however, the effect of molybdate increases significantly at concentrations above 50 mM and leads to a broad passive range. Surface analysis of the samples exposed to inhibitor performed by X-ray photoelectron spectroscopy showed that the inhibitor layers consist of oxides of multiple valences. Scanning electron microscopy with chemical analysis was also used to characterise the inhibitor layers. Equilibrium diagrams of the aqueous species in the selected concentration range were generated to better understand the inhibition mechanism and to correlate the electrochemical data and data on surface properties.