Zinc is a well-known sacrificial coating material for iron and co-deposition of suitable particles is of interest for further improving its corrosion protection performance. However, incorporation of particles that are well dispersible in aqueous electrolytes, such as silica particles, is extremely difficult. Here, we report a detailed study of Zn-SiO nanocomposite coatings deposited from a zinc sulfate solution at pH 3. The effect of functionalization of the silica particles on the electro-codeposition was investigated. The best incorporation was achieved for particles modified with SiO-SH, dithiooxamide or cysteamine; these particles have functional groups that can strongly interact with zinc and therefore incorporate well into the metal matrix. Other modifications (SiO-NH, SiO-Cl and ,-dimethyldodecylamine) of the silica particles lead to adsorption and entrapment only.

Recently, it was shown that the surface modification of silica particles with -SH functional groups enables their electro-codeposition with zinc. Here, however, we report that no incorporation into Zn can be observed for such modified particles with diameters of <100 nm, while incorporation is possible for particles with diameters of 225 nm and larger. Furthermore, when silica particles are functionalized with mixtures of -SH and -Cl functional groups, which affect the interface energy at the particle/metal interface differently but have similar interfacial energies for the particle/electrolyte interface, it is found that, for successful incorporation of the particles, a minimum amount of -SH functional groups is needed. An explanation for these observations has been derived based on energetic considerations regarding the interfaces involved in the process.

Copper-silica composite coatings were prepared by electro-codeposition on stainless steel substrates. The influence of functionalization and surface charge of SiO2 particles on the electrodeposition of Cu-SiO2 nanocomposite coating was studied. SiO2-SH particles were embedded inside the metal matrix whereas particles with other surface termination did not incorporate inside the metal matrix. Moreover, cysteamine addition to the electrolyte containing bare SiO2 particles induced embedding of particles into the metal matrix. The diameter-dependence of incorporation of -SH functionalized SiO2 particles as well as the role of the density of the effective functional group (-SH) for successful incorporation into Cu have been investigated. Infrared (IR) and X-ray photoelecotron (XPS) spectroscopy were used to observe the interaction of Cu2+ ions with thiol groups, showing a Cu2+ binding. The incorporated particles were found to increase the microhardness of the coating

not Available.