A new self-healing anticorrosion mechanism has been developed as a result of collaborative research conducted at the Max Planck Institute of Colloids and Interfaces in Germany and the University of Aveiro, Portugal. Scientists believe the technology could replace traditional passive measures such as coatings and sacrificial anodes.

‘Corrosion degradation of structural and functional materials leads to losses of about three to four per cent of national product annually in any developed country’, explains Dr Mikhail Zheludkevich of the Surface Engineering and Corrosion Protection Group at the University of Aveiro. ‘Thus effective protection can significantly decrease this negative economic impact. [Our] approach combines the passive barrier and active corrosion protection mechanisms in one system.’ Conventional anti-corrosion silicazirconia sol-gel film matrices are doped with ‘nanocontainers’ that release corrosion inhibitors.

An aluminium alloy 2024 sample coated in a sol-gel film with nanocontainers remained intact following 14 days of immersion in 0.5% molar (M) of sodium salt (b), compared to sample (a) of the same material coated in sol-gel film without nanocontainersZheludkevich says, ‘The main difference is that we are adding organic corrosion inhibitors to the coating, not directly, but in an encapsulated form. [This] prevents interaction with components of the coating, avoiding negative effect on [its] stability and barrier properties.’

Applied through spraying, dipping or painting techniques, the doped films limit corrosion through a ‘smart’ self -healing effect. The polyelectrolyte shell releases benzotriazole in response to changes in pH caused by the onset of corrosion. Once the affected area has been targetted, the nanocontainer closes, preventing further release of the inhibitor. Dr Dmitry Shchukin of the Max Planck Institute explains that there is ‘active feedback between the coating and the localised corrosion processes’

Although further research is required to create nanocontainers with higher inhibitor loading capacity, the team have revealed promising results (see image above, right). Furthermore, another benefit of this technology is that it is more environmentally friendly than other systems in use that contain strong oxidants and heavy metals.