Galvanic Corrosion of a Zn/steel Couple in Aqueous NaCl

Abstract

Galvanic corrosion of a model Zn/steel couple was investigated in aqueous NaCl solutions by measuring open circuit potentials (OCPs), potential and current distributions, and galvanic currents. The OCP transient of the Zn/steel couple was divided into two stages. The first stage consisted of sacrificial dissolution of zinc. At low concentrations of NaCl (0.01 mol/dm 3 ), the cathodic reaction on the couple surface was an oxygen reduction reaction (ORR). With increasing concentrations of NaCl, the cathodic reaction at the steel surface changed from an ORR to the combination of an ORR and hydrogen evolution reaction (HER). In addition, the precipitation morphology of zinc corrosion products differed as a function of NaCl concentration, suggesting that the pH distribution on the couple surface depended on the relationship between the cathodic reactions and the hydrolysis of Zn 2+ . Furthermore, the findings demonstrated that both the ORR and HER were inhibited at the steel underlying precipitated zinc corrosion products. The second stage consisted of steel corrosion. The location of the onset of steel corrosion was related to the pH distribution just prior to the extinction of the galvanic action of zinc.

Corrosion protection of steel cut‐edges by hot‐dip galvanized Al(Zn,Mg) coatings in 1 wt% NaCl: Part I. Experimental study

“…In summary, all our experiments point to the absence of any protective ability of the corrosion products formed on the steel/Al alloy cut‐edges in the immersed condition. This is in opposition to pure zinc coatings, on which stable precipitates form and do block the electrochemical activity . This can be related to the influence of aluminum on the quantity and properties of the corrosion products or to the reduced efficiency of oxygen reduction inhibition in presence of Mg^2+ ions observed in ref.…”

“…This is in opposition to pure zinc coatings, on which stable precipitates form and do block the electrochemical activity. [29,30,31] This can be related to the influence of aluminum on the quantity and properties of the corrosion products or to the reduced efficiency of oxygen reduction inhibition in presence of Mg^2 + ions observed in ref. [32].…”

Respirometric In-Situ Methods for Real-Time Monitoring of Corrosion Rates: Part I. Atmospheric Corrosion

“…This includes the evolution of H2 from pits on corroding aluminium 24,25 or (stainless) steels 26,27 . HER resulting from the galvanic coupling 28 of defective Zn coatings on steel can lead to H2 embrittlement and stress corrosion cracking. A method to quantify the exact contribution of HER and ORR under different exposure conditions is lacking in the literature.…”

Hydrogen Absorption Behavior into Zn and Zn–Al Coated Steels during Corrosion in Aqueous Solutions

“…This is because Zn and Zn-alloy coated steels have good corrosion resistance in mild atmospheric corrosion environments. [8][9][10][11] This is due to the following mechanisms: (1) slow corrosion rate of Zn in atmospheric corrosion environments, (2) galvanic action of Zn can prevent steel surfaces exposed to the atmosphere from corrosion, and (3) corrosion products of Zn can retard occurrence of fatal corrosion and degradation of the steel substrate. However, sacrificial dissolution properties of Zn and Zn alloy coatings to prevent steel corrosion may become a drawback because surface potential of the steels with Zn and Zn alloy coatings can become less noble than that without the coatings, resulting that hydrogen evolution reaction can be enhanced more on the steels with the coatings.…”