The Influence of Inhibitor Ions on Dissolution Kinetics of Al and Mg Using the Artificial Crevice Technique

Abstract

The effect of four anions on dissolution kinetics of Al and Mg in chloride-containing solution was investigated using the artificial crevice technique. Polarization curves for Al and Mg artificial crevice electrodes were obtained by first dissolving the artificial crevice electrode to a fixed depth at a high potential and then scanning the potential downward to the repassivation potential. Potential components were obtained by fitting the polarization curve to an equation describing activation overpotential and ohmic potential drops. Of chromate, dichromate, molybdate, and nitrate, only nitrate was found to inhibit the dissolution kinetics of Al artificial crevice electrodes. In contrast, all anions inhibited the dissolution kinetics of Mg artificial crevice electrodes. The results indicate that the mechanism of localized corrosion inhibition of Al alloys by chromate must be something other than inhibition of anodic dissolution in an active pit or crevice.High strength Al alloys such as AA2024-T3 are widely used in aircraft applications, but are extremely susceptible to localized corrosion. In order to protect them from localized corrosion, protective coatings containing inhibitors, typically chromates, must be used. Chromates (or dichromates) dissolved in solution are also extremely effective in inhibiting corrosion, even at dilute concentrations.

Corrosion protection of AA2024-T3 by LDH conversion films. Analysis of SVET results

“…Some level of corrosion retardation may also be attributed to both NO 3 -and Zn 2+ , as described in the literature. Nitrates have been reported as species displaying inhibiting properties on aluminium alloys [14], even when intercalated in LDH-based powders [15]. On the other hand, Zn 2+ entrapped in the LDHs films during the synthesis step can work as cathodic inhibitor by precipitating as hydroxides on the cathodic areas, as pointed out by Buchheit and colleagues [16].…”

Real-Time Monitoring of Aluminum Crevice Corrosion and Its Inhibition by Vanadates with Multiple Beam Interferometry in a Surface Forces Apparatus

“…Even though, in principle, it is experimentally possible to monitor initial pitting corrosion at an openly exposed surface, a real time monitoring of crevice corrosion or the internal pit site is extremely challenging. Lead-in-pencil or artificial pit electrodes, [22][23][24][25][26][27] Normansky interference contrast microscopy, 5 artificial crevices techniques, 28 X-ray micro-tomography, 29 synchrotron based micro-tomography, 30 as well as electrode arrays 31 have all been used to study crevice corrosion under various conditions. However, to our knowledge, an Ångstrom resolved real-time visualization of the initiation of crevice corrosion inside a confined environment has not been experimentally demonstrated.…”

Localized Corrosion of Al-Based Amorphous-Nanocrystalline Alloys with Solute-Lean Nanocrystals: Pit Stabilization

“…Thus, it facilitates a study of the kinetics of a stable, active pit of known size ͑in depth and area͒ with 1D mass transport out of the pit. Since the early artificial pit studies, the technique has been used extensively to study the effects of alloying elements and inhibitors on pit growth and repassivation kinetics of Al alloys, 16,43,49,50 stainless steels, 44,[51][52][53][54] and the characteristics of pit growth and repassivation in pure Al. 49,50,[55][56][57] An artificial pit is generated by inducing the extensive dissolution of a pencil-like microelectrode embedded in epoxy or a glass tube to create a deep pit with inert sides and an active bottom with constant area.…”