Synthesis of hybrid silica sol–gel coatings containing Zn particles on carbon steel and Al/Zn coated carbon steel

Owing to increasing interest of coatings applied on low alloy steel and galvanised metal plates and their applications, this work presents the study of the process requirements to be fulfilled in order to coat these metals with an hybrid silica coatings containing Zn particles. The main idea was to combine the “barrier” effect of the hybrid silica coatings with the “active protection” effect of the zinc particles inside the coatings. Sol–gel parameters, Zn particles content and suspension stability have been studied. EMPHOS ES 21, an electrostatic dispersant, has been used to obtain stabilised suspensions. Thick, adherent and crack-free coatings containing 10% Zn particles were prepared by dip-coating on carbon steel and Al/Zn coated carbon steel substrates. The applied coating seems to improve corrosion protection of the two metal substrates, and this effect is more noticeable in the case of the Al/Zn system because of the combination of the complementary corrosion protection properties of both coatings.