The Electrolytic Codeposition of Silica and Titania Modified Silica with Zinc

This paper describes the electrolytic codeposition of pure and titania modified spherical silica particles with zinc from zinc sulfate electrolytes on a rotating disk electrode. The adsorption of zinc ions onto silica and the morphology of composite zinc-silica coatings as a function of the pH of the plating solution were investigated. It was found that the adsorption of zinc ions onto silica, the codeposition of silica, and the formation of hydroxides increase with pH. Titania modified silica particles were found to codeposit at low pH. Their incorporation In zinc from low pH electrolytes is explained based on an electrode blocking effect by the adsorbed particles leading to a local pH increase in the vicinity of the cathode. This leads to the formation of zinc hydroxides which causes silica particles to be codeposited with zinc even from plating solutions of low bulk pH.