Exploring the potential of silicate-based corrosion inhibition for copper in dynamic salt water environment

Sodium silicate (SS) and a sodium alginate–sodium silicate inhibitor blend (SASS) are investigated as sustainable green corrosion inhibitors for copper in saline environment under both static and dynamic flow conditions. Potentiodynamic scans and Electrochemical Impedance Spectroscopy revealed that SS is protective in both static and flowing water conditions (up to 86 and 97% resp.). A significant link is also found between the increasing overall film resistivity at increasing silicate concentrations (up to 5 and 10 mM SS for static and dynamic testing, respectively) and the decreasing film’s defect density via Mott-Schottky. Furthermore, the acquires EIS and M-S results revealed that a separate silicate-based film is formed on top of a copper oxide film. By flow speed variation, the importance of silicate-diffusion on the inhibition mechanism and film’s defect structure is also studied. The combination of SS and SA results in a synergistic SASS blend, showing a clear improvement of the corrosion properties. However, higher silicate concentrations (5 mM SS) are required in this blend to reach optimal inhibition efficiencies. While inhibition by SS decreases the efficiency with increasing water hardness, incorporation of SS into a SASS blend alternatively increases the effectiveness with increasing hardness, reaching optimal inhibition at 50 ppm ${\mathrm{Ca}}^{2+}$. A mechanism is proposed, in which ${\mathrm{Ca}}^{2+}$ and ${\mathrm{Mg}}^{2+}$ act as network formers for the formed SA-SS film structure.