Corrosion of cadmium plating by runway de-icing chemicals in cyclic tests: Effects of chemical concentration and plating quality

Abstract Concentration of de-icing chemicals used at airfields in Northern countries may vary significantly, due to the dilution caused by rain and melting ice or snow. Furthermore, quality variations in cadmium platings used in aircraft components are a common fact. In this study, we examine the influence of the de-icing chemical concentration and the plating quality on the corrosion of cadmium using two cyclic corrosion tests: Boeing and AMS G-12 tests. The tests are performed using four de-icers: pure potassium formate, pure potassium acetate and two commercial chemicals containing these salts, at three concentrations, and four types of cadmium plating. The obtained results show that the extent of corrosion of the cadmium plating decreases with decrease in de-icing chemical concentration. The changes in characteristics of the chemicals, such as pH value, electrical conductivity and the amount of dissolved oxygen, due to changes in concentration, do not unambiguously explain the observation. Rather, the conditions during heat–humidity exposure, particularly the employed temperature, are of key importance. Wetting behavior of the chemicals on the four types of cadmium plating discloses slight differences between the plating types but more distinct differences between the used potassium formates and potassium acetates. A more efficient wetting of cadmium platings by potassium formates than potassium acetates yields one explanation why potassium formates introduce more severe corrosion damage. Concerning the cadmium plating quality, thickness and the amount and distribution of pores are the key parameters in terms of corrosion performance. In this paper, these results are presented and discussed in the light of published literature.