Multilayered coatings: Tuneable protection for metals

The role of oxide bi-layers in controlling the onset of corrosion has been explored. A high-throughput electrochemical approach was employed to determine the breakdown potential of aluminium metal over-coated with combinations of silicon, titanium, aluminium and magnesium oxides. Bi-layered coatings consisting of two 100 nm thick metal oxide layers provided increased protection against breakdown, and combinations with vastly different iso-electric point of solid (IEPS) were found to exhibit improved barrier properties in comparison to single-component oxides. Furthermore, the most protective oxide bi-layers were produced when a high IEPS oxide was deposited directly onto the metal surface and subsequently over-coated with a low IEPS oxide. The barrier properties of bi-layer coatings appear to be tuneable, with notable dependencies on surface charge and thickness.