Galvanic Corrosion in the Copper/Zinc System: I. Potential distribution in relation to the nature of the cathode and to the type of anion in solution

Abstract

The open circuit potentials of Cu, Zn and three brasses were followed as a function of time in 0.1 M solutions of KCI, KNO₃ and Na₂SO₄ until steady-state values were obtained. For Cu and the brasses the steady-state potentials were practically the same and were approached from more negative values; those for Zn were reached from more positive values. The differences between the two sets of figures varied between 800–1000 mV, depending on the nature of the solution. The implications of these figures in the galvanic corrosion of Zn are discussed.

The electrochemical potentials on the surface of the Cu (brass)/Zn bimetallic combinations. measured in the X and Y directions in the three test solutions, invariably gave S-shaped curves, with the less negative potentials on the Cu side. A double transformation procedure gave the potential distribution over the surface of the bimetallic combinations. Two types of potential distribution pattern were obtained. depending on the cathode material and on the composition of the solution.

The actual corrosion currents were measured and compared with the loss in weight of the Zn anode (expressed in coulombs). The highest values were found with the Cu/Zn system in cr solutions. Both potential scanning and the measurement of the galvanic corrosion currents revealed that no galvanic corrosion took place between pairs involving copper and any of the three alloys, nor between pairs of the Cu-Zn alloys.