Mesoporous silica coatings with improved corrosion protection properties

• Mesoporous silica coatings were prepared on Zn substrates against corrosion.
• Electrochemical investigations gave evidences about the protective action.
• Inhibitors were incorporated into the pores for ensuring self-healing properties.
• The inhibitor can be trapped in the pores by rendering the coating hydrophobic.
• Corrosion protection can also be improved by rendering the coating hydrophobic.

Sub-micrometer thin, compact and mesoporous silica coatings were prepared on Zn substrates by sol–gel method, aiming the replacement of traditional chromates conversion coatings and pretreatments. The effect of layer thickness, porosity and the character of pore structure, number of thermal treatments, and various silylating agents were studied on the anti-corrosion behavior of the coatings, systematically and comparatively. The surface-, structural-, and optical properties of various silica thin films were characterized with different methods thoroughly. The corrosion resistance of the coatings was comparatively evaluated by open circuit potential measurements, Tafel interpretation of the polarization curves, and electrochemical impedance spectroscopy. Thicker films have better anti-corrosion property, as expected. More interestingly, we show that porous layers can have such a good corrosion resistance as compact films. This fact has special importance when impregnation with inhibitor would be applied. Furthermore, rendering the coatings hydrophobic improves the corrosion resistance of both porous and compact coatings significantly. The character of pore structure, the type of silylating agents, and the thermal treatment applied between two consecutive dippings do not affect notably the protective properties of the silica films. Furthermore, we demonstrate the difference in the accessibility of the pores in the case of ordered and disordered pore structure.

Figure optionsDownload as PowerPoint slide