Influence of SiO2 particles on zinc-nickel electrodeposition

Zinc-nickel/SiO2 electrodeposits have been produced from an acid sulphate bath. The complimentary (mutual) codeposition behaviour of SiO2 and nickel was observed. The presence of SiO2 in the zinc- nickel bath appears to change the alloy deposition behaviour. Rate of nickel deposition was considerably increased with SiO2 particles in the bath. Similarly, nickel ions were found to enhance the rate of SiO2 incorporation. The effect of particle size studied revealed that the rate of incorporation of larger (2 mm) particles was higher than that of the smaller (20 nm) particles. Changes in hydrodynamic conditions of the composite bath seem to influence the mass transport of nickel ions hence there is a notable increase in the rate of nickel deposition and SiO2 incorporation. Morphological studies show that the presence of SiO2 in the bath seems to have a marked effect on the morphology and microstructure of the zinc-nickel coatings. Cathodic polarisation studies carried out during electrodeposition show a decrease in cathodic current densities with increasing SiO2 concentration in the bath.