Combatting corrosion with smart, green protective coatings
EU-funded researchers have developed smart multifunctional coatings to combat corrosion on aircraft components and car parts in order to lower maintenance costs and protect the environment.
© Brad Pict #240579687, source:stock.adobe.com 2020
Corrosion whether rust on your car, on an aircraft or in the steel support of a bridge is a serious, common and costly problem. Widely used metals such as magnesium and zinc alloys, galvanised steel or aluminium are typically covered with protective layers of paint, powder coating or chrome plating, but even a small scratch can become a magnet for corrosion that could weaken the materials structural integrity if not promptly repaired.
Researchers in the EU-funded MULTISURF project set out to counter corrosion in a smarter and more proactive way, exploring techniques to create coatings that can repair themselves. The teams approach harnessed the unique properties of layered double hydroxide (LDH) an ion-exchange compound capable of forming multifunctional protective layers, engineered to activate anti-corrosion properties at the first sign of damage or exposure to corrosive conditions.
Active protective coatings are complex material systems consisting of multiple components and designed for specific structures used in specific environments, says project coordinator Mikhail Zheludkevich at the Helmholtz-Zentrum Geesthacht Centre for Materials and Coastal Research in Germany. The main feature of these conversion coatings is their potential to be loaded with different functional agents, which can be released on demand and can activate a desired effect under the influence of an external trigger.
An LDH-based conversion layer loaded with corrosion inhibitor, for example, would release the anti-corrosion agent if exposed to conditions that would normally cause oxidation, such as coming into contact with air or water, thereby providing active protection. Alternatively, the conversion layer could incorporate other types of functional agents, such as compounds designed to repel liquids, counteract contamination, inhibit or release odours, or even kill bacteria.
Cleaner than chrome
In the aeronautical industry, for instance, active protective LDH coatings could lower maintenance costs on aircraft and extend service intervals. Innovative coating solutions could also reduce the sectors environmental impact by substituting toxic chromate pre-treatments that are widely used to protect metal components in aircraft.
The integration of corrosion inhibitors close to the metal surface opens up a promising way for improved long-term performance of coating systems in challenging environments, Zheludkevich says. In addition to aviation, other industrial sectors, such as automotive or civil engineering, also need active protective systems to ensure long-term service performance.
The MULTISURF team developed novel LDH surface treatments for magnesium and aluminium alloys, opening up a wide range of possibilities to design active protective coatings for those materials. The researchers also demonstrated, for the first time, the LDH-based sealing of anodic layers on aluminium alloys, displaying effective active corrosion protection and better performance than current sealing solutions.
The technologies we developed are currently being optimised and are undergoing industrial testing, focused on exploring their potential as an alternative to toxic chromate-based treatments, Zheludkevich says.
Ongoing research and development is being carried out in Germany in a nationally funded initiative led by MULTISURF partner Airbus, as well as a number of other initiatives. These include a follow-on Marie Skłodowska-Curie Research and Innovation Staff Exchange project called FUNCOAT in which LDH particles are being considered as functional additives in plasma electrolytic oxidation, an environmentally friendly electrochemical surface treatment for metals.
MUTISURF has also led to the creation of a summer school on functional surface treatment at the University of Aveiro in Portugal, attracting PhD students and early-stage researchers from across Europe.
The project has delivered many important scientific results and new scientific knowledge that is now being shared about the potential of LDH-functional surface treatments for a variety of materials, Zheludkevich concludes.