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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - MULTISURF (MULTI-functional metallic SURFaces via active Layered Double Hydroxide treatments)

Teaser

Summary

The second half of MULTISURF project was dedicated to the investigation of mechanism of LDH formation on the surface of active metals as well as screening of different functionalities, which can be added together with active corrosion protection.
Using synchrotron facilities (HZG outstation - DESY/Hamburg), it was shown, that anionic exchange in LDH nanocontainers happens much faster in comparison with expected previously.
This result is significantly important for further TRL increase of the KDH formation and functionalization processes, since it leads to the reduction of time and respectively costs of the conversion treatment. In parallel to this work, the concept of dissolution modulators was developed for direct LDH growth on the surface of magnesium alloys as explained in overall project achievements. Within close collaboration between the partners of MUTISURF consortium, for a first time ZnAl LDH was synthesized directly on both pure zinc and zinc galvanized steel. The solubility of aluminum compound in electrolyte was found to be a critical issue for this synthesis. However, optimization of temperature, pH, time and other parameters let us perform this synthesis and load the formed LDH with corrosion inhibitors. This approach was further tested for corrosion protection and confirm its effectiveness. One can expect, that further optimization of the process parameters will let is possible the treatment of real automotive details against corrosion and effective LDH use for industrial application. In addition to active corrosion protection, LDH based nanocontainers were tested for providing antifouling, hydrophobic and sensing functionalities. It was shown and presented in the technical (confidential) part of the report, that this functionalities can be reached with LDH via anionic exchange. However, the TRL of these results is still low and additional work is required.

Work performed

The work in frame of MULTISURF project was focused on the surface modification of active metals (aluminum, magnesium and zinc) via LDH (layered double hydroxides) formation and it further functionalization via anion exchange reaction. Two main hybrid treatments for aluminum alloys have been in focus during MULTISURF project:
â€¢ Plasma electrolytic oxidation (PEO) in combination with LDH treatment. PEO is an advanced anodizing process leading to the formation of ceramic-like coatings under high-voltage discharges in eco-friendly alkaline electrolytes.
â€¢ Anodizing pretreatments (Tartaric sulfuric acid anodizing (TSA) and phosphoric sulfuric acid anodizing (PSA)), which is environmentally-friendly anodizing method, suitable for aeronautic application and developed for toxic Cr(VI) replacement, followed by LDH sealing.
For both of them, LDH-based sealing was used as a post-treatment in order to achieve active corrosion protection performed on aluminum alloy AA2024. The obtained results clearly demonstrate that such an active sealing enhances the total corrosion protection performance and ensure effective healing of the artificial defects suppressing active corrosion processes.
A principally novel approach was developed during the MULTISURF project for direct LDH growth on the surface of magnesium alloys. The modulators of Mg and Al solubility we applied in order to keep suitable concentration of required components for the LDH formation in the pH range, where LDH can be formed. This way let us overcome the principle problems, which significantly limited the possibility of its application for real industrial needs:
â€¢ No autoclave conditions are required for LDH formation anymore. This leads to significant increase of chance that LDH based conversion treatment will be adopted for automotive and aerospace application,
â€¢ No carbonates are required for LDH formation. In other words, the formation of functionalizable LDH is reached and confirmed.
Further, this approach was extended to the LDH growth on PEO Mg alloy AZ91 (Fig. S-1).
Within close collaboration between the partners of MUTISURF consortium, for a first time ZnAl LDH was synthesized directly on both pure zinc and zinc galvanized steel. The solubility of aluminum compound in electrolyte was found to be a critical issue for this synthesis. However, optimization of temperature, pH, time and other parameters let us perform this synthesis and load the formed LDH with corrosion inhibitors. This approach was further tested for corrosion protection and confirm its effectiveness. One can expect, that further optimization of the process parameters will let is possible the treatment of real automotive details against corrosion and effective LDH use for industrial application.
Overall, we have develop the number of systems, based on the LDH formation on surface of active aluminum, magnesium and zinc alloys (bare and pre-anodized), which are suitable for further functionalization (corrosion protection, corrosion sensing, hydrophobisation, etc.) and fulfill real industrial demands. This work was performed during the secondments (94,33%% of secondments was implemented). International, intersectorial and mixed secondments took place. Early stage researchers were actively involved in this process.
The obtained scientific results were distributed for a broad community via seminars, scientific publications (incl. Open Access publications), conferences and lecturing.

Final results

The most significant progress beyond state of the art is achieved in the direction of active LDH-treatments for Al, Mg and Zn alloys as it is already briefly mentioned above. The developed coatings demonstrate well-defined self-healing ability and confer superior corrosion protection performance in comparison to the currently used commercial processes. Industrial attractiveness of the developed processes is even further increased by reducing the treatment temperature and time when Li-based bathes are employed in order to form LiAl-LDH structures in the anodic layers.
A principally novel approach was developed during the MULTISURF project for direct LDH growth on the surface of Mg alloys. The modulators of Mg and Al solubility we applied in order to keep suitable concentration of required components for the LDH formation in the pH range, where LDH can be formed. This way let us overcome the principle problems of LDH formation on the magnesium surface, which significantly limited the possibility of its application for real industrial needs (autoclave and carbonates, as it was expleined before).
Further, this approach was extended to the LDH growth on PEO Mg alloy AZ91. Moreover, the mixture of modulators was used in order to achieve the effective sealing of PEO pores (Figure S-1), improving barrier behaviour of the layer as well as adding functionalization with inhibitors.
For a first time ZnAl LDH was synthesized directly on both pure zinc and zinc galvanized steel. The solubility of aluminum compound in electrolyte was found to be a critical issue for this synthesis. However, optimization of temperature, pH, time and other parameters let us perform this synthesis and load the formed LDH with corrosion inhibitors. One can expect, that further optimization of the process parameters will let is possible the treatment of real automotive details against corrosion and effective LDH use for industrial application.