Formation and electrochemical properties of the superhydrophobic nanocomposite coating on PEO pretreated Mg-Mn-Ce magnesium alloy

This paper describes the methods of preparation and electrochemical properties of hydrophobic (HP) and superhydrophobic (SHP) nanocomposite coatings on the surface of magnesium alloy pretreated using plasma electrolytic oxidation (PEO). The most effective corrosion protection in brine solutions among the coatings under study was demonstrated by the nanocomposite superhydrophobic coating. For this coating, the values of the contact and rolling angles are 166 degrees +/- 3 and 5 degrees +/- 3 degrees, respectively. The impedance modulus (vertical bar Z vertical bar(f) (= 0.005)) value, which characterizes the anticorrosion properties, attains 2.5 . 10(7) Omega cm(2) for the SHP coating and 1.4 . 10(6) Omega cm(2) for the HP coating at the initial moment of immersion into a chloride-containing electrolyte, thus improving the resistance of the base PEO coating by almost 400 and 20 times, respectively. After 24 h of exposure, the protective properties of the SHP coatings are one order of magnitude higher than those of the HP coatings. The high corrosion resistance and considerable stability of the SHP coatings during their operation result from a small area of real contact with aggressive media due to a heterogeneous wetting regime and formation of a firm chemical bond between the molecules of the hydrophobic agent and the other coating components. (C) 2013 Elsevier B.V. All rights reserved.