Encapsulation and incorporation of sodium molybdate in polyurethane coatings and study of its corrosion inhibition on mild steel

• Sodium molybdate provides corrosion protection on steel in brackish water.
• Sodium molybdate is encapsulated using interfacial polymerization.
• Capsules are characterized and their inhibitor load is determined.
• Coatings with incorporated capsules show improved corrosion performance.

Sodium molybdate is evaluated as corrosion inhibitor for steel in brackish water; it is encapsulated by interfacial polymerization and the produced capsules are characterized. Electrochemical impedance spectroscopy and corrosion potential measurements were used to determine the short-time corrosion inhibition while polarization curves were used for the estimation of the inhibition efficiency. The capsules composition, the Na2MoO4 content and the release rate are then determined. Na2MoO4 shows corrosion inhibition for at least 15 h. Capsules consist of polyurea and polyurethane which are formed due to the reaction of the isocyanates with the water of the emulsion and the used surfactants, respectively. Most of the inhibitor is released within 90 min. Electrochemical Impedance Spectroscopy and Scanning Vibrating Electrode Technique show corrosion inhibition on artificially damaged areas for the coatings containing the corrosion inhibitor capsules.