​​​​CONVPROTECT​

Aluminium and magnesium alloys have been the main choice for structural applications in aeronautical industry due to their superior mechanical properties when compared to other metal alloys. Nevertheless, aluminium and magnesium alloys are very reactive and prone to corrosion attack, which may limit their performance and ultimately cause failure with unpredictable consequences. The state-of-art technology for corrosion protection of
metallic structures in aeronautical industry generally consists of application of a multilayer coating system, comprising several layers with different roles and functionalities, namely a conversion film that is grown onto the metallic substrate to promote adhesion between the metal and subsequent coating layers, a primer which is an organic coating layer where anticorrosion pigments are dispersed to provide active corrosion protection and a topcoat to provide additional barrier (passive) effect and aesthetics.

This project aims at the development of conversion films based on layered double hydroxides (LDHs). LDHs are anion-exchangers that have been prepared as particulates and successfully used as smart nanocontainers for corrosion inhibitors when added to organic and hybrid matrices. In LDHs the release of corrosion inhibitors occurs in a controlled manner triggered by the presence of aggressive anions (e.g. chlorides), with the (anionic) corrosion inhibitor being released and the aggressive anion entrapped. This project proposes an extrapolation of the concept of nanocontainer to nanostructured film grown directly on the metallic substrate, using layered double hydroxides (LDHs) crystallites as building block units. Although there are some reports of synthesis of LDH conversion films, they involve complex methodologies. More importantly, they do not render active corrosion protection because corrosion inhibitors are not present, only passive protection (through barrier effect) is provided. The latter is important but not sufficient, especially when defects occur in the film and healing of defects by inhibitors is required.

The resulting LDH conversion films will then be tested using different surface characterization, spectroscopic and electrochemical techniques in order to evaluate the anticorrosion performance of the resulting films. The most promising LDH systems will then be tested in conditions more close to industrial application, namely as part of multilayer systems and also in complex shapes.

The objectives of this poject are:

• Synthesis of LDH conversion films in metal alloys and optimization of experimental conditions to promote formation of LDH phases.

• Intercalation of corrosion inhibitors.

• Development of multifunctional LDH conversion films with both active corrosion protection and hydrophobic properties.

• Testing of anticorrosion performance of LDH films in multilayer systems and complex shapes.