Protective cerium-containing sol-gel coatings on hot-dip galvanized steel

Due to the high toxicity of chromating solutions that contain highly toxic hexavalent chromium compounds and the conversion coatings formed in these solutions, most countries have adopted laws restricting or completely banning the use of Cr(VI) compounds in engineering and electronics products.This publication deals with the development of a process for application of protective sol-gel cerium-containing coatings on the surface of galvanized steel.The compositions of solutions for the deposition of self-sufficient protective/decorative or adhesive coatings have been optimized, and the physicochemical and mechanical properties of the coatings that can potentially be employed instead of toxic chromate coatings have been studied.It has been found that sol-gel coatings formed in an alkaline sol of cerium dioxide (pH 9.5-10) at 4-6 mm/min sample withdrawal rate feature the highest protective ability.Subsequent heat treatment of cerium-containing sol-gel coatings at a temperature of 300°C has been shown to enhance the protective characteristics.It has been shown that at the optimum rate of withdrawing a sample from the sol, coatings with a thickness of 100-120 nm are formed.It has been established that the time before the appearance of the first white corrosion spots on the ceriumcontaining coatings studied is 70 h, which matches the 72 h period established by the ISO 9227 standard for iridescent chromate coatings.Taking into account the results obtained, this technology can be used to obtain functional coatings with protective properties on the surface of galvanized steel.They can be used as protective and decorative coatings in automotive, machine building, instrumentation, aircraft, shipbuilding, chemical and petrochemical and other industries.