Characterization of the corrosion products of electrodeposited Zn, Zn–Co and Zn–Mn alloys coatings

Synergistic effects of additives on morphology, texture and discharge mechanism of zinc during electrodeposition

Nanocrystalline zinc coatings were produced by pulse electrodeposition in acid sulfate bath containing thiourea and benzalacetone additives and characterized by X-ray diffraction and scanning electron microscopy techniques. The influence of benzalacetone concentration and pulse peak current density on the grain size and crystallographic orientation of zinc deposits was investigated. Zinc electrodeposited from additive-free solutions or with one of the two additives is not composed of nanosized crystals. The mixture additives of thiourea and benzalacetone give rise to the formation of particle-like nanocrystalline zinc with a (10ī1) random orientation. A change in peak current density from 2 to 1 A/cm2 only increases the grain size from 60 to 62 nm.

Electrodeposition of nanocrystalline zinc from acidic sulfate solutions containing thiourea and benzalacetone as additives

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.

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

The influence of polyethylene glycol (PEG), cetyltrimethylammonium bromide (CTAB), benzalacetone (BA), and thiourea (TU) on pulse electrodeposition of zinc from acidic sulfate baths was investigated by X-ray diffraction, scanning electron microscopy, and potentiodynamic polarization techniques. The results show that a mixture of PEG and CTAB can fully dissolve BA in the concentrated zinc sulfate solutions. This ternary additive can increase the overpotential of zinc electrodeposition markedly, and then gives rise to forming a bright nanocrystalline zinc coating on steel substrate, with an average grain size of 52 nm. The combination of these four compounds is more powerful for improving the cathodic polarization and inhibit hydrogen evolution during zinc electrodeposition in comparison with ternary additive systems. A bright and compact zinc coating with a grain size of 43 nm and the (110)(100)(201) preferred orientations are produced due to the coexistence of all four compounds. These compounds act in a synergetic way, especially between BA and TU, leading to the grain refinement of zinc deposits.

https://iopscience.iop.org/article/10.1149/1.2772093/pdf

Effect of Additives on Electrodeposition of Nanocrystalline Zinc from Acidic Sulfate Solutions

The transformation products of benzylidene acetone formed during zinc electrodeposition in solutions containing a nonionic surfactant and/or carboxylic acid were determined by IR and 1H NMR-spectra after extraction and chromatographic separation. 1-Phenylbutanone-3, 1-phenylbutanole-3 and 1-phenylbutane were cathodic reaction products. Benzaldehyde, acetone, benzyl alcohol and benzoic acid were chemical reaction products in the cathodic layer. The nonionic surfactant increased the solubility of benzylidene acetone and carboxylic acid. This effect is probably caused by hydrophobic interaction and formation of associates. The associates cover a larger area of the cathodic surface than unsaturated ketone and/or carboxylic acid alone. It is supposed that a synergistic effect of additive mixtures on zinc electrodeposition may be caused by the formation of associates.

G. Bernotienė

Papers

Behaviour of benzylidene acetone during zinc electrodeposition in weakly acid solution containing a nonionic surfactant and/or carboxylic acid