Cathode current efficiency (CCE) of Zn/SiO 2 composite electrodeposition bath was investigated. Influence of current density, particle loading, bath agitation, deposition time and bath additive were given particular attention. It was revealed that CCE and particle content in the deposit were inversely proportional to one another with increase in particle loading up to 80g/l, beyond which both decreased. Influence of time on CCE for different particle loadings shows that CCE was significantly higher for baths with lower amount of particles than those with higher amount of particles. However, CCE shows an increasing trend with bath agitation for both 13g/l and 26g/l particle loading with that of 26g/l being higher for all amplitudes investigated. Also, addition of NaNO 3 additive into the bath was found to improve the CCE of the bath. Influence of current density was investigated for a bath with 104g/l of SiO 2. The results show a sharp decrease in CCE from current density of 15A/dm 2 and were constant for higher current densities up to 30A/dm 2. Morphological changes accompanied changes in CCE.
Composite electrodeposits of Zn-Ni/SiO 2 were produced electrolytically using direct current. Their corrosion resistance characteristics were investigated through the use of neutral salt spray, linear polarisation resistance and potentiodynamic anodic polarisation methods. Neutral salt spray data shows that times to 5% red rust were longer for the coatings embedded with SiO 2 particles than those without particles. Effect of current density shows that deposits produced at higher current densities consistently exhibited a tendency to decrease in corrosion resistance. In addition, the linear polarisation resistance of coatings containing SiO 2 tends to increase with increasing particle content up to 5.5wt% SiO 2 and then decreases. However, there was no significant difference observed for the anodic dissolution current densities for coatings containing SiO 2 particles and their SiO 2-free counterparts. The mode of protection appears to be a combination of sacrificial and barrier protection to the underlying steel substrate
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