Electrodeposition and corrosion behavior of Zn coatings formed using as brighteners arene additives of different structure

Abstract

This study examined the effect of the molecular structure of the aliphatic chain in arenes (phenyl + aliphatic chain) used as brightener additives on the reduction kinetics, morphology and corrosion resistance of Zn coatings formed by reduction of Zn(II) ions in a chloride electrolytic bath. Three such brighteners were tested—benzylideneacetone (BDA), benzylacetone (BA) and butylbenzene (BB)—dissolved in polyethyleneglycol (MW200) PEG 200, in order to determine the influence of the phenyl, carbonyl and/or C = C double bond present in these compounds on the zinc reduction process. The results showed that, in the presence of PEG 200 alone, the reduction rate (j 0) of Zn(II) ions was higher than in the absence of additives. By contrast, in the presence of the brightener-PEG 200 mixtures, the values of j 0 were lower, leading to a reduction in the size of the Zn clusters. Among the brighteners tested, no significant differences were observed in the values of j 0 as a function of the molecular structure of the arene aliphatic chain. SEM analysis revealed a change in the Zn coating morphology from hexagonal crystals with a (101) preferred orientation in the absence of additives, to flakes grouped in hemispherical clusters with (002), (100) and (101) crystallographic orientations when PEG 200 or brightener-PEG 200 mixtures were present in the electrolytic bath. In addition, the cluster size decreased in accordance with the j 0 values. The comparison of the values of corrosion current density indicates that there are no significant differences between them.