Corrosion Protection of Mg Based Alloy in Neutral Sodium Chloride Solution By Electrodeposited Ni-TiO2 – Silane Composite Coating

Abstract

The electrochemical behavior of magnesium based alloy (composition Mg(93) Zn(1) Al(6) alloy) is studied in corrosive media of 3.5% NaCl aqueous electrolyte solution. Electrochemical techniques including D.C polarization and electrochemical impedance (EIS) measurements are used to characterize the behavior of the alloy. The data indicated the direct dissolution of the alloy as evidenced from ICP measurements and surface examination after exposure to the corrosive media. The alloy then was treated with a silane-polymer coating that proved effective protection to the surface of the alloy against corrosion. Another approach is applied to improve the corrosion protection ability and film quality to the magnesium-based alloy based on the electro – deposition of another metal layer on top of the surface of the alloy. The Ni/TiO2 – silane composite layer was applied to the electrode to serve as a protective layer for the alloy. First the nickel and TiO2 nanoparticles was applied to the surface of the alloy followed by a protective silane film either by sequential spin-coating or layer-by-layer spin-coating. The protecting film is composed of 1,2bis(triethoxysilyl)ethanepoly(vinyl alcohol) hybrid (TESEPVA). Surface examination of the alloy or film-coated alloy was performed before and after exposure to the corroding electrolyte. The surface techniques used are field-emission scanning electron microscopy (FE-SEM) with energy dispersive X-ray analysis, X-ray photoelectron spectroscopy (XPS) and surface enhanced Raman spectroscopy (SERS). The film thickness and surface wettability were also determined with the film displaying relative increase in the hydrophobic character.