Sodium molybdate as a corrosion inhibitor for aluminium in H3PO4 solution

The inhibition effect of sodium molybdate (Na2MoO4) on the corrosion of aluminium in 1.0 M H3PO4 solution was studied by weight loss, potentiodynamic polarisation curves and electrochemical impedance spectroscopy (EIS) methods. The results show that Na2MoO4 is a good inhibitor, and the inhibition efficiency obtained by three methods is higher than 84% at 20 mM. The adsorption of Na2MoO4 obeys Freundlich isotherm at lower concentrations (1–7 mM), while Langmuir isotherm at higher concentrations (7–20 mM). Polarisation curves indicate that Na2MoO4 acts as an anodic inhibitor. EIS spectra exhibit three loops (two capacitive loops and one inductive loop).

► Na2MoO4 is a good inhibitor for the corrosion of aluminium in 1.0 M H3PO4.
► The adsorption isotherm depends on Na2MoO4 concentration. Namely, the adsorption obeys Freundlich adsorption isotherm at low concentration, while Langmuir adsorption isotherm at higher concentration.
► Potentiodynamic polarisation curves reveal that Na2MoO4 is an anodic inhibitor.
► EIS spectra exhibit a large capacitive loop at high frequencies, a small inductive loop at medium frequencies and a second capacitive loop at low frequencies.