Einfluß der Kationenzusammensetzung von Chloridlösungen beim Modellieren von Korrosionseinflüssen der Küstenatmosphären

Influence of the cation composition of chloride solutions in modelling corrosion effects due to caoastal atmospheres Pure sodium chloride solutions cannto be used for accelerated weathering tests in artificial sea atmosphere. A spray liquid suitable for such tests is artificial seawater containing (grams/litre) 27 NaCl, 6 Mg chloride, 1 Ca chloride and 1 KCl. The corrosion behaviour of the two metals studied – iron and zinc – is characterized by typical differences, in particular variations depending on the salt quantity applied. While the corrosion of iron at first increases with the salt concentration applied and achieves a maximum at about 1000 mg/m²d, the losses of zinc increase just to a salt quantity of 200 mg/m² d and are then practically constant up to about 1000 mg/m²d; at higher concentrations there is again a slight diminuation of corrosion. The corrosion in artificial seawater is more pronounced than in sodium chloride solutions; this fact can be attributed to the hydrolysis of the chlorides in seawater, which gives rise to the formation of anodic and cathodic regions on the metal surface; as a consequence, pH differences are created and corrosion is enhanced. In order to simulate natural conditions as closely as possible the application of the salt spray should be interrupted by extended dry periods.