“SMART” protective ability of water based epoxy coatings loaded with CaCO3 microbeads impregnated with corrosion inhibitors applied on AA2024 substrates

By Snihirova, Darya; Lamaka, Sviatlana V. & Montemor, M.F.
Published in Electrochimica Acta NULL 2012

Abstract

Corrosion protection of aluminium alloys often relies on the application of a coating on the metallic surface. The coating normally combines a barrier effect that restricts the ingress of corrosive species, with an inhibitive role induced by corrosion inhibitor pigments added to the coating formulation. However, the direct addition of corrosion inhibitors to the coating can cause some detrimental interactions between components, as well as formation of preferential electrolyte pathways, compromising the barrier properties. Moreover, electrolyte uptake and ageing may result in leaching of those corrosion inhibitors. In order to extend the corrosion inhibition ability of organic coatings one possible solution is to store the inhibitors inside nano or microreservoirs compatible with the coating matrix and able to sense the local changes induced by the corrosion process. This strategy has led to the development of a new generation of “smart� coatings for anti-corrosion purposes. The aim of this work is to study the anti-corrosion properties of water-based epoxy coatings loaded with pH sensitive particles, acting as feedback active containers for corrosion inhibitors and applied on the aluminium alloy AA2024-T3. For this purpose micron size calcium carbonate beads were modified with different corrosion inhibitors: cerium nitrate, salicylaldoxime and 2,5-dimercapto-1,3,4-thiadiazolate. These particles act as pH sensitive reservoirs because they dissolve at acidic pH, releasing the corrosion inhibitor, which then suppresses the corrosion activity of the bare metal. Electrochemical impedance spectroscopy (EIS) was used to estimate the electrical parameters assigned to the barrier properties of the coating and corrosion inhibition ability in the presence of inhibitor loaded calcium carbonate beads. The most relevant corrosion inhibition effects were observed from CaCO3 microbeads modified with cerium ions. The self healing potential of this new system was corroborated by localised electrochemical impedance measurements (LEIS).

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