The investigation of the passive behaviour of copper in weakly acid and alkaline solutions and the examination of the passive film by esca and ISS

Abstract

The passive behaviour of copper is examined in weakly acid and alkaline solutions. The current peaks of the potentiodynamic polarization curves are related to the formation and reduction of passivating oxide layers. These layers have been examined by ESCA and ISS. A duplex structure of the oxide is found with copper I oxide at the metal surface covered by copper II hydroxide for sufficiently positive potentials. The thickness of the anodically formed oxide is deduced from the charges of cathodic reduction in phosphate buffer pH = 7.0 and 8.0 and borax buffer pH = 9.2. 10 to 14 Å of Cu 2O are found for the three buffer solutions not changing decisively with the potential of passivation. The thickness of the covering Cu(OH) 2 is increasing with the potential in the range of 0.30 V H to 1.20 V H up to 33, 23, and 19Å in the buffer solutions pH = 7.0, 8.0, and 9.2, respectively. From the increase of the thickness of the Cu(OH) 2 layer with the potential an electrical field strength of ∼ 5<d10 6 V cm −1 is deduced for the outer part of the passive layer.