Influence of formulation and application parameters on the performances of a sol–gel/clay nanocomposite on the corrosion resistance of hot-dip galvanized steel. Part I. Study of the sol preparation parameters

• Modifying the pH has a direct impact on the nanoclay dispersion.
• pH strongly affects the rheology of nanoclays containing sol–gel solutions.
• pH and hydrolysis time affect the protection properties of the sol–gel coatings.
• Longer hydrolysis times are necessary to obtain a protective film.

This work deals with the investigation of a sol–gel/nanoclay composite coating as a protective layer for the corrosion protection of hot-dip galvanized (HDG) steel. Sol–gel coatings prepared from glycidoxypropyltrimethoxysilane, tetraethoxysilane and methyltriethoxysilane with 2 wt.% of sodium montmorillonite were investigated. As the first part of a complete study, this paper investigates the effect of the formulation parameters on the performance of the composite layer. In particular, the parameters affecting sol preparation and the hydrolysis conditions (such as pH, ultrasonication time,…) were studied as well as their effects on the final corrosion protection properties of the composite layer. The experimental findings highlighted that modifying the pH has a direct impact on the nanoclay dispersion. The investigation of the rheological behavior of the suspension evidenced significant interactions between the particles. In particular, specific interactions between the silanol groups and the nanoclays were observed from FT-IR and indirectly confirmed by the study of the influence of the delay between pH adjustment and addition of the precursors on the properties of the coating. These interactions were correlated to the corrosion protection efficiency of the composite layers.