Composition and properties of methyl silicate/silicate composite coatings

Abstract

Methyl silicate/silicate composite coatings were prepared using a two-step method. The morphology, chemical composition, hydrophobicity and corrosion resistance of the coatings were investigated by scanning electron microscope (SEM) with energy dispersive spectrometer (EDS), Fourier transform infrared spectroscopy (FT-IR), contact angle tests, neutral salt spray (NSS) tests and potentiodynamic polarization curve, respectively, and were compared with those of single silicate coating and methyl silicate coating. The corrosion mechanism of methyl silicate/silicate composite coatings were analysed by electrochemical impedance spectroscopy (EIS) as well as equivalent circuit. The results show that the compositions of methyl silicate/silicate composite coatings outer layer are the almost same as the compositions of single methyl silicate coating, different from single methyl silicate coating with lots of cracks on surface, the composite coatings are uniform and smooth with no crack, and the adhesion is good. Single silicate coating is hydrophilic. Compared with single silicate coating, methyl silicate/silicate composite coating is hydrophobic, corrosion inhibition of cathodic process is obviously enhanced, and polarization impedance of the composite coating is 5 times more than that of the single silicate coating,total impedance values of composite coatings are more than 100 kΩ·cm2, corrosion current density of composite coatings is reduced by 60%.

Keywords

• sodium methyl silicate
• hydrophobicity
• silicate composite coating
• corrosion resistance