Novel Protective Coatings Based on Nanoparticles and Nanocapsules for the Corrosion Protection of Magnesium Alloys

Modern nanochemistry offers many possibilities for the corrosion protection of materials. Inorganic coatings based on nanoparticles can be applied under conditions which are typically only suitable for organic coatings. In a facile procedure, up to 1.5 µm thick coatings based on aqueous commercial SiO₂-nanoparticle dispersions and soluble binders (e.g. B(OH)₃, Na₂HPO₄) can be applied even onto thermally precarious magnesium alloys. These coatings are also excellent primers for acidic coating sols which would otherwise react with the substrate. Besides good protective properties and mechanical and thermal stability, these vitreous, sustainable coatings enable to keep the decorative metallic appearance, as requested e.g. for cases and rims.

Nanochemistry can also improve the corrosion performance of existing coating systems. Incorporated into common anodized barrier layers, nanocontainers could provide the triggered release of chemicals. After physical damage, encapsulated monomers which are capable of forming hydrophobic, self-assembling monolayers could repel the attack of water and aggressive anions. In case of corrosion encapsulated inhibitors could prevent further corrosion.

Electrochemical impedance spectroscopy, potentiodynamic polarisation experiments and salt spray tests were used to systematically examine the protective properties of these coatings. Especially incorporated inorganic inhibitors, i.e. lanthanide salts, help to improve the corrosion performance.