Development and testing of nano-porous micro-carriers for corrosion inhibitor release from protective organic coatings

The use of carriers doped with environmentally friendly corrosion inhibitors has been proposed in the last years as an alternative to existing highly efficient but toxic corrosion inhibitors based on chromium VI. Despite the promising results using synthetically produced nano-carriers, limitations related to their production and protection of big damages makes the search for carrier alternatives necessary step for a successful introduction of the concept in industrial applications. This work explores for the first time the feasibility of using a biobased nano-porous silica micro-carrier obtained from the exoskeletons (frustules) of the algae group known as diatoms.

For the doping, frustules obtained from diatomaceous earth (fossil frustules) of one location where the main diatom species is Aulacoseira and Ce(NO3)3 as corrosion inhibitor were used. In order to evaluate the doping degree and release kinetics of the diatom frustules a new in-situ detection system was developed and validated. Out of this detailed study, one diatom-doped system was selected for further proof of the active corrosion protection in a coating system. For the purpose an epoxy coating and an aerospace aluminium alloy AA2024-T3 were used. The protection degree was then evaluated by an in-situ opto-electrochemical technique, combining crucial optical information about delamination and underfilm corrosion processes with electrochemical signals. In order to advice on the best possible carrier geometry for active corrosion protection and establish the first steps to the theoretical limits of the concept, a modeling approach was followed.

For the doping, frustules obtained from diatomaceous earth (fossil frustules) of one location where the main diatom species is Aulacoseira and Ce(NO3)3 as corrosion inhibitor were used. In order to evaluate the doping degree and release kinetics of the diatom frustules a new in-situ detection system was developed and validated. Out of this detailed study, one diatom-doped system was selected for further proof of the active corrosion protection in a coating system. For the purpose an epoxy coating and an aerospace aluminium alloy AA2024-T3 were used. The protection degree was then evaluated by an in-situ opto-electrochemical technique, combining crucial optical information about delamination and underfilm corrosion processes with electrochemical signals. In order to advice on the best possible carrier geometry for active corrosion protection and establish the first steps to the theoretical limits of the concept, a modeling approach was followed.

The work presented here demonstrates that the use of diatom frustules as carriers for active corrosion inhibition in coatings is feasible and very promising. The results show that, without further optimization of the formulation or the doping and release mechanism, protection of AA2024 coated plates of up to 27 days immersion in 0.05 M NaCl are possible. Moreover, two in-situ evaluation set-ups have been proposed and validated allowing future research in a much more efficient and reliable manner. Furthermore, the model applied in this work shows that the corrosion protection can be tuned by the carrier size and further optimized by using shapes with a high aspect ratio, combined with the implementation of controlled release systems and more efficient inhibiting agents. This work sets up the basis for future research in the use of the big diatom family with more than 10.000 different architectures as carriers for controlled release in coatings.

http://resolver.tudelft.nl/uuid:4c7eb631-977b-4848-b21d-8e15c39623d6

Type: Master Thesis
Publication: Repository TU Delft
Faculty of Aerospace Engineering, Novel Aerospace Materials.
Date: December 2015

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