Anticorrosive behavior study by localized electrochemical techniques of sol–gel coatings loaded with smart nanocontainers

In the present work, sodium phosphomolybdate, an environmentally friendly corrosion inhibitor with good anticorrosive behavior when applied on steel substrates, has been loaded and encapsulated in mesoporous silica nanoparticles without and with a hollow core in order to produce different smart nanocontainers. These nanocontainers have been designed to allow controlled release of the inhibitor in response to an external stimulus, thereby achieving more efficient and more economical use of the active substance. Corrosion activity leads to local changes in pH, and this work considers such changes as a signal of great interest. The nanocontainers respond to a pH of 10 or higher by increasing the release rate of the encapsulated active material. The smart nanocontainers have been incorporated into hybrid organic–inorganic sol–gel coatings and applied on carbon steel substrates. Mechanical defects have been made in the organic coating, reaching through to the metallic substrate, in order to study anticorrosive behavior in the affected area. A characterization study has been carried out at the defects and in their surroundings by means of two different localized electrochemical techniques: Scanning Kelvin Probe and Localized Electrochemical Impedance Spectroscopy. The results have shown significant improvement in the anticorrosive behavior of sol–gel coatings when formulated with smart nanocontainers loaded with sodium phosphomolybdate compared to a reference sol–gel coating.