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 II. Effect of curing temperature and time

The study 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. The effect of different curing times (2, 5, 10, 15. min) and different curing temperatures (90 °C, 150 °C, 180 °C) on the protection properties of the hybrid layer was investigated. ToF-SIMS analyses and FT-IR measurements highlighted that the higher is the curing temperature, the higher is the densification of the sol-gel network. FT-IR spectroscopy measurements underlined that the Si-O-Si/Si-OH ratio rises by increasing curing time or temperature. ToF-SIMS analyses indicate a lessening in the coating thickness by increasing the curing temperature. The densification of the network through formation of siloxane bonds was found to be responsible for the improved protection offered by the sol-gel layer which leads to a remarkable drop of the cathodic current density and an increase of the resistance associated to the sol-gel film.