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 elect rolytes on a rotating disk electrode. The adsorption of zinc ions onto silica and the morphology of composite zinc-silica coatings as a func tion of the pH of the plating solution were investigated. It was found that the adsorption of zinc ions onto silica, the codeposition of sil ica, and the formation of hydroxides increase with pH. Titania modifie d silica particles were found to codeposit at low pH. Their incorporat ion In zinc from low pH electrolytes is explained based on an electrod e blocking effect by the adsorbed particles leading to a local pH incr ease in the vicinity of the cathode. This leads to the formation of zi nc hydroxides which causes silica particles to be codeposited with zin c even from plating solutions of low bulk pH.