Effect of Na3VO4 Inhibitor on the Corrosion Resistance of Al2Cu Intermetallic Phase in H3PO4 Aqueous Solution

Sodium orthovanadate was tested as a corrosion inhibitor of intermetallic Al₂Cu in 1 M H₃PO₄. The Al₂Cu–H₃PO₄–Na₃VO₄system was studied using the following methods: inductively coupled plasma optical emission spectrometry, scanning electron microscopy with energy dispersive x-ray spectroscopy, x-ray diffraction, electrochemical impedance spectroscopy, polarisation and open circuit potential. It was found that the corrosion rate decreased as the inhibitor concentration increased. The highest inhibition efficiency 99% was obtained when sodium orthovanadate initial concentration was equal to 100 mM, pH = 1.11, due to precipitation of a protective layer of insoluble salt, containing vanadium, phosphorus, sodium and oxygen, on the surface. At pH = 0.76 the protective layer was not formed and inhibition efficiency decreased to 76%. Selective corrosion of the intermetallic phase caused a significant increase of an electric double layer capacitance and decrease of a charge transfer resistance.