Corrosion protection of mild steel by polyvinylsilsesquioxanes coatings in 3% NaCl solution

Polyvinylsilsesquioxanes (PVS) coatings were synthesized by the hydrolytic polycondensation of vinyltrimethoxysilane using hydrochloric acid as a catalyst. Their structure was characterized by Fourier transform IR (FTIR) and the viscosity [in centipoise(cP)] of polyvinylsilsesquioxanes was measured at 298 K. The electrochemical behavior of I-IV coated steel electrodes, of polymer concentration as follows: [I(20%), II(40%) of viscosity 50 cP and III(20%), IV(40%) of viscosity 15 cP], was investigated in 3% NaCl solution using various electrochemical techniques, i.e., open-circuit potential (OCP), potentiodynamic polarization, electrochemical impedance measurements (EIS), and surface examination via scanning electron microscope (SEM) technique. The influence of immersion time on the electroctrochemical behavior of polysilsesquioxane-coated electrodes was also studied. The results of polarization measurements showed that corrosion current density (i(corr)) decreases in the order IV > III > II > I. Also, the film resistance is the highest for PVS-coated electrode I as evaluated from EIS measurements. OCP, EIS, and polarization results are in good agreement with each other. The obtained results were confirmed by surface examination using scanning electron microscope.