Corrosion resistance of laser-nanostructured galvanized steel modified with alkylphosphonic acid

The paper suggests a method for protection of galvanized steel from atmospheric corrosion, which involves the laser treatment of its surface followed by exposure to an ethanolic solution of octadecylphosphonic acid (С18Р). The advantages of the proposed method include its environmental safety and high anticorrosion efficiency, along with a small thickness of films formed (up to 10 nm) and the use of low concentrations of the non-toxic organic corrosion inhibitor. The surface morphology, composition, hydrophobic and anticorrosion properties of thin films formed with С18Р on laser-nanostructured surface of galvanized steel were studied by SEM, EDX, XPS, water contact angle measurement and corrosion tests. It is shown that laser treatment of the surface of galvanized steel gives it a polymodal morphology and enriches the surface layer of metal with zinc oxides, including non-stoichiometric zinc oxide (Zn0.44O0.56). Such preparation of the metal surface makes it possible to obtain stable superhydrophobic protective films (the water contact angle reaches 163±2°) in a solution of С18Р. С18Р chemisorbs on a zinc coating, forming an ultrathin protective film consisting of zinc octadecylphosphonate, ZnO and Zn(OH)2, as well as physically adsorbed С18Р molecules. The combination of the superhydrophobic properties of the alkylphosphonate film with its structure and strong adsorption causes its high anticorrosion efficiency in a corrosive atmosphere of 100% relative humidity with condensation of moisture on the surface and in a neutral salt spray atmosphere.