Controlled adsorption of titanium(IV) oxide particles on electroplated zinc coatings to improve the corrosion resistance of chromium(VI)‐free conversion layers

Adsorption of nano-scaled titanium(IV) oxide particles on electroplated zinc is per-formed by a simple dip-coating technique in an aqueous titanium(IV) oxide suspen-sion prepared with a stirred media mill. X-ray photoelectron spectroscopy, scanningelectron microscopy and X-ray fluorescence spectroscopy are carried out to inves-tigate the composition of the zinc surface and the thickness and porosity of the ad-sorbed titania films. The zinc surface formed during the electrodeposition processis of oxyhydroxide nature and the thickness of the adsorbed titania particle layer iscontrolled by the pH value and the solid concentration of the suspension. In therange of 10 wt.%–30 wt.% titanium(IV) oxide, a linear dependence between the tita-nia film thickness and the solid content of titania particles in the suspension isfound. Highest film thicknesses are obtained in alkaline media (pH9). At13.5 wt.% titania particles and pH values below pH=2.4, the titania particle film isnot closely packed and the zinc layer underneath is still visible in electron micro-scopy, which is a prerequisite for imbedding these particles by a thin second zinclayer for formation of a robust chromium(VI)-free passivation layer containing thetitania particles.