The spatial distribution of Zn{sup}(2+) during galvanic corrosion of a Zn/steel couple

摘要

The spatial distribution of Zn{sup}(2+) during galvanic corrosion of a model Zn/steel couple in 0.01 M NaCl was investigated using a scanning zinc disk electrode. The couple had a coplanar arrangement of a steel substrate with an electroplated zinc layer at the center. During galvanic corrosion, the marked changes in the Zn{sup}(2+) concentration were confined to a thin solution layer ca. 1.0 mm thick above the couple surface. In this thin solution layer above the zinc layer, a higher concentration region of Zn{sup}(2+) in the range of 5-18 mM extended around the zinc layer in the solution during galvanic corrosion. Conversely, above the steel surface distant from the zinc layer, the surface concentration of Zn{sup}(2+) was almost zero during galvanic corrosion. On this surface, the precipitation of zinc corrosion products due to the hydrolysis reaction of Zn{sup}(2+) was observed. The distribution of the Zn{sup}(2+) concentration supported that Zn{sup}(2+)acted as a buffer that suppressed the increased pH due to the cathodic reaction on the steel surface near the zinc layer and almost no corrosion products formed there. The spatial distribution of Zn{sup}(2+) is discussed in relation to the distributions of potential and pH and the surface morphology of the galvanic couple.