Sol‐Gel/Polyelectrolyte Active Corrosion Protection System

This work presents a new type of feed‐back active coating with inhibitor‐containing reservoirs for corrosion protection of metallic substrates. The reservoirs are composed of stratified layers of oppositely charged polyelectrolytes deposited on AA2024 aluminum alloy coated with hybrid sol‐gel film. The layer‐by‐layer assembled polyelectrolyte film with the entrapped corrosion inhibitor is constructed by sequential spray‐coating deposition of water solutions of poly(ethyleneimine), poly(sodium styrenesulfonate) and 8‐hydroxyquiniline on the top of the sol‐gel coating. The active corrosion protection of AA2024 alloy coated with SiO₂/ZrO₂ sol‐gel film and modified by polyelectrolytes is demonstrated by electrochemical impedance spectroscopy and scanning vibrating electrode technique. The results obtained here show that polyelectrolyte films deposited atop of the hybrid sol‐gel coating on AA2024 alloy remarkably improve the long‐term protection performance providing additional “intelligent” anticorrosion effect that results from delivery of inhibiting species “on demand”. This becomes possible since the configuration of the polyelectrolyte molecules depends on the presence of H⁺ ions making the polyelectrolyte film sensitive to the pH of the surrounding solution. The source of local pH changes is the corrosion process starting in the micro‐ and nano‐defects leading to increased permeability of the polyelectrolyte reservoir and, consequently, to controllable release of entrapped inhibitor.