Investigation of polysiloxane coatings as corrosion inhibitors of zinc surfaces

The corrosion behavior of zinc platelets coated with different polysiloxane layers was investigated using impedance spectroscopy (IS) and measurements of the linear polarization resistance (LPR). Values of the polarization resistance derived were used for the calculation of the corresponding corrosion current densities and the degree of surface passivation. The two electrochemical methods used are both suitable for the characterization of the corrosion protective properties of siloxane layers by considering that a higher polarization resistance results from a better sealed surface and, therefore, indicates a more effective corrosion inhibiting coating. After testing several siloxane layer systems, a three siloxane layer system was developed, forming a stable network, bonded to the zinc surface by covalent bonds and acting as hydrophobic barrier to corrosive media. The corrosion protective properties of these layer systems lead to a significant increase in the corrosion resistance of zinc surfaces, clearly exceeding that of chromate conversion coatings.