Effects of Organic Additives on Initial Stages of Zinc Electroplating on Iron

Abstract

Effects of organic additives such as benzoic acid ͑BA͒ and poly͑ethylene glycols͒ ͑PEGs͒ on the initial stages of zinc electroplating were investigated at an iron electrode using cyclic voltammetry, energy-dispersive spectroscopy, soft X-ray absorption spectroscopy, and electrochemical impedance spectroscopy in an acidic zinc chloride solution. BA mainly contributed to the roughness control of the zinc layer with a relatively weak interaction with zinc ions. However, PEG molecules raise the overpotential for reduction of both zinc ions and protons by effectively blocking the electrode surface. Soft X-ray absorption spectroscopic results confirmed that the iron oxide layer was reduced to metallic iron by electrodeposited zinc prior to zinc bulk deposition. Impedance measurements helped reveal the roles of BA and PEG molecules during the zinc deposition on the surface and also in determining the corrosion behavior of zinc plated iron. Zinc electroplating has been widely used in the steel industry for the protection of steel products in corrosive environments. Various organic compounds have been proposed as additives for zinc electroplating and extensively studied to obtain durable, uniform, and compact zinc coatings for corrosion prevention of steel products. [1][2][3][4][5] These organic molecules or mineral impurities added to the electroplating solution were known to exert crucial influences on the qualities and corrosion characteristics of the electrodeposits.6-9 The effects of the organic molecules on the bulk electrodeposition process itself and the physical characteristics of the electrodeposited layers have been examined by voltammetric, radiometric, and electrochemical impedance spectroscopic studies. 10-16The initial electrodeposition process was reported to affect the mechanical properties of electrodeposits. 1,7 When the work function of a metal being electrodeposited is lower than that of the substrate metal, the electrodeposition may occur at a potential more positive than the equilibrium potential, a phenomenon called underpotential deposition ͑UPD͒.17 On the basis of the Kolb-Gerischer relation, 18,19 an underpotential shift (⌬E) of 0.15-0.20 V is estimated for the zinc UPD on an iron substrate. Effects of adanions, as well as the pH of the solution, on the kinetics of the zinc UPD, hydrogen adsorption, and resulting morphology of the deposit have been investigated extensively at noble metal electrodes using electrochemical and scanning tunneling microscopy techniques. 20-29 Also, zinc UPD has been studied at iron or steel electrodes in connection with the hydrogen evolution reaction. 30,31 Despite all these studies, the way in which additives affect the substrate/zinc layer/electrolyte interfaces during the initial electrodeposition on the iron electrode is poorly understood. In this work, we study the effects of the organic molecules primarily on the initial stages of zinc electrodeposition, employing various electrochemical and spectroscopic techniques. The roles played by the organic molecules ...

Effects of SiC and Al2O3 particles on the electrodeposition of Zn, Co and ZnCo. I. Electrodeposition in the absence of SiC and Al2O3

“…It can be attributed to Zn underpotential deposition (upd) [34,49] and Zn upd together with HER [25, 27,30,[50][51][52]. Some authors, such as Lee et al [31], consider that in this region nucleation of Zn competes with the HER. Others suggest that zinc hydroxide is formed on steel in this region, owing to the high H 3 O ?…”

“…competes with Zn 2? at active sites for adsorption [30,31,58, 59], a smaller area of steel is expected to be covered by Zn upd under forced convection conditions. These pre-bulk electrodeposition processes, as will be seen later, affect the bulk electrodeposition.…”

“…Zn electrodeposition can be performed in alkaline or acid baths [24]. Current research on acid baths is mainly devoted to the effects of organic additives on Zn electrodeposition [25][26][27][28][29][30][31][32]. Alloying of Zn with small quantities of Co increases its corrosion resistance [33].…”

Voltammetric and morphological characterization of zinc electrodeposition from acid electrolytes containing boric–polyalcohol complexes

“…Lee et al [3] studied the effects of organic additives such as benzoic acid (BA) and polyethylene glycol (PEG) on the initial stages of zinc electroplating. BA mainly contributed to the control of roughness of the zinc layer, interacting weakly with zinc ions.…”

Deposition of Zn–Cr alloy coatings from sulfate electrolyte: effect of polypropylene glycol 620 and glycine and combinations thereof

“…In a manner similar to that of PEG, PPG 620 obviously slows down the growth of the Zn coating. Adsorption of PPG 620 blocks sites active for Zn ion reduction, thus hindering the surface diffusion and acting as a barrier to the transport of protons and Zn ions towards the electrode surface [24]. On the other hand, oxygen atoms in the PPG 620 molecule may act as electron-pair donors to Zn 2+ and are likely to form complexes with the Zn ions.…”