Electrodissolution Kinetics of Iron in Chloride Solutions: VI . Concentrated Acidic Solutions

Abstract

Anodic iron dissolution in acidic chloride solutions (constant ionic strength of 4.5M) over a wide range of H + and C1-concentrations has been investigated. Anodic dissolution in low [H+]-concentrated chloride solutions is accelerated by both C1-and OH-with Tafel slopes of 0.075 V/decade at low polarization and accelerated by only OH-with Tafel slopes of 0.04 V/decade at high polarization. On the other hand, anodic dissolution in highly acidicconcentrated chloride solutions is accelerated by both H + and C1-with Tafel slopes of 0.11 V/decade and first-order dependence on both H + and C1-. For low C1-concentrations in either dilute or concentrated acidic solutions, anodic dissolution is inhibited by C1-. The experimental results indicate that anodic iron dissolution in acidic chloride solutions proceeds by simultaneous parallel reactions. Mechanisms which are consistent with the empirical rate expressions have been developed.

Formation mechanism and protective property of corrosion product scale on X70 steel under supercritical CO 2 environment

“…This finding indicates that the addition of NaCl dramatically increased the dissolution rate of the steel during the initial corrosion stage. Cl -could form intermediate corrosive species and thus accelerate the active dissolution of steels during the scale-free CO 2 corrosion process [51,[58][59]. The anodic catalytic reaction process can be described as follows [51]:…”

Effect of sodium chloride on corrosion of mild steel in CO2-saturated brines

“…The second effect is that solution pH is decreased by adding more NaCl due to higher activity of H ? [10][11][12][13][14], which accelerates corrosion kinetics. The third role is that it reduces CO 2 solubility, which leads to a slower corrosion.…”

“…In deaerated acidic solutions, chloride accelerates the anodic kinetics of iron dissolution via a catalytic mechanism [11][12][13][14]. In deaerated neutral and alkaline solutions, a corrosion scale is usually formed.…”

The Dissolution Mechanism of Iron in Chloride Solutions

“…Their experiments in [xNaC1 + yHC1, x + y = 4.5M] solutions contradict some of the findings of earlier work (4), but in agreement with the work of Chin (5) show that the polarization curve has two quite distinct Tafel slopes. At low polarization potentials, the rate is accelerated by chloride ions and hydroxide ions with a Tafel slope of 0.075 V/decade where the proposed mechanism is kl Fe" H20 + C1-~ FeC1OH + H § --> Fe 2+ + C1-+ H20 [3] At high polarization potentials the rate is accelerated by hydroxide ions with a Tafel slope of 0.04 V/decade and the predominant process is the mechanism ka Fe. H~O FeOH § + H + ---> Fe 2+ + H~O [6] The purpose of our work is to add to the experiments of Kuo and Nobe by measuring the electrochemical impedance iron corroding in chloride solutions of constant ionic strength over a range of frequencies, pH's, and potentials.…”