Breakdown of Oxide Films on Steel Exposed to Chloride Solutions

Abstract

Breakdown of the thin air-formed oxide film is the first step in the corrosion of steel exposed to aqueous chloride environments. We studied oxide-film breakdown by observing changes, with time, of appearance, weight loss, and corrosion potential while varying the three components of the system: environment, substrate, and film. Environment was varied by changes in chloride and hydrogen peroxide concentrations. Low carbon steel, stainless steel, aluminum, and titanium substrates were studied. Various types of crystalline oxide film were applied to steel substrates by RF sputtering. The results of this work demonstrated that the chemical and electronic properties of the oxide film on steel are inconsequential in determining whether film-breakdown will occur. We interpret these results in terms of a film-breakdown mechanism in which substrate dissolution begins at film defects and spreads, thus causing removal of the film by undercutting. According to this model, the ability of the substrate to spontaneously reform a stable oxide and repair the film determines resistance to film-breakdown.

An amino‐based protic ionic liquid as a corrosion inhibitor of mild steel in aqueous chloride solutions

“…When clean steel is exposed to dry air, it is usually covered with a transparent oxide film, but then if the steel is placed in an aggressive environment such as chloride solutions, corrosion accompanied by a loss of the air-formed film takes place, which can be recognized by a drop in potential. [42] Such behavior was found for steel in uninhibited solution (0.01 mol/L sodium chloride, pH 6). In the first seconds, it is possible to identify this thin airformed oxide layer by a relatively high OCP.…”

“…After a few seconds, the OCP dropped down constantly, since there is a loss of air-formed oxide layer, with onset iron dissolution and formation of corrosion product. [42] Chloride ions have a particular influence on this breakdown, it being well accepted that the amount of chloride ions is directly related to how fast this breakdown occurs. This is probably caused by the attraction of Cl − ions toward steel speeding up the breakdown and formation of corrosion products, as stated by Gabrielli et al 42,43 and Liengen et al [44] The results for 0.01 mol/L sodium chloride, pH 9 are also shown in Figure 2a,b.…”

“…[42] Chloride ions have a particular influence on this breakdown, it being well accepted that the amount of chloride ions is directly related to how fast this breakdown occurs. This is probably caused by the attraction of Cl − ions toward steel speeding up the breakdown and formation of corrosion products, as stated by Gabrielli et al 42,43 and Liengen et al [44] The results for 0.01 mol/L sodium chloride, pH 9 are also shown in Figure 2a,b. The behavior is similar to that of uninhibited steel in the presence of chloride solution in pH 6, with only one particular difference, the time to breakdown the air-formed oxide was longer at pH 9.…”