Corrosion of cadmium plating by runway de-icing chemicals: Study of surface phenomena and comparison of corrosion tests

In this paper, we study the corrosion of cadmium plating by four runway de-icing chemicals using electrochemical measurements and standard (immersion) and proposed (cyclic) runway de-icing corrosion tests for cadmium plating. Besides the obtained electrochemical and gravimetric data, we analyze the exposed surfaces by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and infra-red spectroscopy (IR). The chemicals included in the tests are pure potassium formate, pure potassium acetate and the corresponding commercial chemicals. Examinations revealed two parallel and linked phenomena on the plating surface, i.e., anodic dissolution of cadmium and development of corrosion products, primarily cadmium carbonate, CdCO3. Electrochemical measurements disclosed that the formed corrosion products slightly improved corrosion resistance of the surface but definitely did not stop corrosion completely, probably due to discontinuous structure. As for the studied de-icing chemicals, potassium formates systematically introduced more segmented corrosion products than potassium acetates and, subsequently, more severe corrosion on the specimens. Immersion cadmium corrosion test did not give very reliable results due to relatively low introduced corrosion rates and very large occasional scatter in the results. Cyclic cadmium corrosion tests introduced relatively greater corrosion rates and somewhat lower deviations than the immersion test, being hence, more reliable, but also more challenging in terms of meeting the weight change criteria for passing the test.