Galvanokinetic Behaviour of Cu in Na 3 PO 4 –NaCl Aqueous Media

Abstract

Galvanodynamic excursions of Cu in 0·1 Na₃PO₄ (pH 12·5) yielded two distinct anodic transients in addition to a third ill-defined one, plus two well-defined cathodic potential arrests. A simple method of calculation, from the galvanodynamic trace, of the quantity of electricity consumed along each process is proposed. Addition of Na₂SO₄ was found to decrease the total quantity of electricity needed to anodically passivate the electrode. cl⁻ addition increased the quantity of electricity corresponding to each anodic process, but by different amounts. At [Cl⁻] = 1 M, the passivating film did not resist the Cl⁻ attack and signs of rapid breakdown of passivity were observed. A series of steps explaining the effect of Cl⁻, involving adsorption, interaction with soluble Cu-hydroxy intermediates and finally peptisation of the deposited oxide, is discussed.