EFFECT OF SIO2 COLLOID ON THE ELECTRODEPOSITION OF ZINC-IRON GROUP METAL ALLOY COMPOSITES

The mechanism of codeposition in Zn-based composite platings has yet to be clarified in detail. In this study, electro-deposition of Zn-Fe group metal-SiO2 composite was performed from the electrolytes containing Zn, Fe group metal cations, and SiO2 colloid. An induced codeposition was found between Fe group metal and SiO2 colloid. This result is explained from the adsorption of Fe group metal ions on SiO2 colloid and the agglomeration of SiO2 colloid on the cathode. Extending this knowledge to the Zn-Cr-SiO2 system composites contain Cr and SiO2 contents of up to 18 and 10 weight percent, respectively, have been obtained for the first time. In this system, SiO2 catalyzed the Cr codeposition. These composites showed excellent corrosion resistance.