Anti-corrosion behavior of epoxy composite coatings containing molybdate-loaded mesoporous silica

In this study, mesoporous silica nanocontainers (MS) were successfully synthesized, functionalized and loaded with sodium molybdate as a corrosion inhibitor (MSInh). The epoxy composite coatings were applied on the mild steel substrates by embedding 1 wt. % mesoporous silica with (E/MSInh) or without (E/MS) inhibitor. Characterization of the synthesized mesoporous silica loaded with molybdate demonstrated the pH-dependence of molybdate release from E/MSInh. According to the results, by increasing the pH from 1 to 14, a 160 times increase in the molybdate concentration in the solution was observed. The corrosion behavior of the composite coatings was assessed by the electrochemical impedance spectroscopy and the electrochemical noise analysis. Charge transfer resistance decreased from 4 x 10(7) to 3.1 x 10(4) Omega cm(2) and from 2.2 x 10(6) to 2 x 10(3) Omega cm(2) for E/MSInh and E/MS during the immersion time, respectively. The results revealed the higher corrosion resistance of E/MSInh during 56 days of immersion in 3.5 wt. % NaCl solutions in comparison to E/MS which confirms the proper corrosion inhibiting effect of the released molybdate ions.