Corrosion Inhibition Of AA2024-T3 Research Articles

Corrosion inhibition of AA2024-T3 in alkaline solution by disodium-N-dodecyliminodiacetate: Experimental and theoretical studies

To enhance the corrosion resistance of AA2024-T3 in 0.01 mol·L−1 NaOH aqueous solution, the inhibition characteristics of the amphoteric surfactant disodium-N-dodecyliminodiacetate (RNC-12) were assessed by means of the static weight loss method, electrochemical impedance spectroscopy, potentiodynamic polarisation curves, atomic force microscopy and X-ray photoelectron spectroscopy, and the results were compared with those of sodium laurate (SL). Quantum chemical calculations and molecular dynamics (MD) simulations were also performed to predict and analyse the relationships between the molecular structure and inhibition efficiency. The results of the experiments revealed that RNC-12 achieved a higher inhibition efficiency of 91% as a valid inhibitor of AA2024-T3 in alkaline medium compared with SL (81%). The results of surface analysis showed that the two inhibitors could be well adsorbed on the alloy surface, and the degree of surface corrosion was as follows: without inhibitor >SL >RNC-12. Quantum chemical calculations and MD simulations showed that the anionic state of RNC-12 possesses a smaller band gap, larger dipole moment, and more negative energy of adsorption, indicating that RNC-12 is more easily adsorbed on the alloy surface than SL. Therefore, the experimental results were in accordance with the theoretical calculations.

Corrosion inhibition of AA2024-T3 by a coating containing dual-pH sensitive, corrosion inhibitor loaded microspheres

In this study, we describe a smart coating that responds to either an increase or a decrease in pH to assist inhibitor effectiveness. Dual-pH sensitive microspheres containing a corrosion inhibitor were fabricated using a simple, template-free, one-step process. A polyelectrolyte coacervate consisting of polyacrylic acid and polyethylenimine was the shell material of microspheres that enclosed Ce(NO3)3 inhibitor using a coaxial electrospray method. The Ce(NO3)3-loaded microspheres with a core-shell structure can release Ce(NO3)3 at both acidic and alkaline pH. A smart coating consisting of these microspheres embedded in a polyvinyl butyral coating releases Ce(NO3)3 to improve the corrosion resistance of AA2024-T3.

The synergistic effect of cerium acetate and sodium sulphate on corrosion inhibition of AA2024-T3 at various temperatures

The present work examines the corrosion inhibition of aluminium alloy 2024-T3 immersed in NaCl+Ce(OAc)3 and NaCl+Ce(OAc)3+Na2SO4 solutions to evaluate the synergetic effect between cerium and sulphate ions at various temperatures (5 °C, 25 °C and 50 °C). The electrochemical properties were studied using short-term potentiodynamic measurements and long-term electrochemical impedance measurements. The surface topography, morphology and composition of cerium deposits formed on the alloy surface after two days of immersion were evaluated using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The results revealed an efficient long-term (up to 8 weeks) corrosion inhibition in NaCl+Ce(OAc)3 that was superior in the NaCl+Ce(OAc)3+Na2SO4 solution, especially at lower temperatures (5 °C > 25 °C > 50 °C). The composition of the Ce-based film varied with the temperature and the presence of Na2SO4, resulting in different mixtures of Ce(III) and Ce(IV) species. The synergistic effect of cerium and sulphate ions on corrosion inhibition was reflected by a higher degree of cerium oxidation from Ce3+ to Ce4+ at a low temperature and the incorporation of sulphates into the formed film, which protected the surface from the corrosion medium more efficiently.

Corrosion Inhibition of AA2024-T3 By Smart Polyelectrolyte Coacervates Responsive to Both Acidic and Alkaline Environments

Previously reported pH-responsive corrosion-protective coatings based on the layer-by-layer assembled polyelectrolytes responded to either a pH increase or decrease caused by cathodic or anodic reactions in corrosion, respectively, but not to both. The layer-by-layer technique, which is the standard method to prepare these coatings, requires dozens of layers to make the coatings useful for corrosion protection by safely enclosing corrosion inhibitors. In this study, polyacrylic acid was directly added into polyethylenimine to make polyelectrolyte coacervates via electrostatic interactions. The coating consisting of polyelectrolyte coacervates was capable of entrapping the SrCrO4 inhibitor and releasing the inhibitor at both acidic and alkaline pH. The concentration of released SrCrO4 exceeded the threshold for the corrosion protection of AA2024-T3 and the corrosion resistance of AA2024-T3 was improved, as evidenced by electrochemical methods including cyclic potentiodynamic polarization and electrochemical impedance spectroscopy. The developed polyelectrolyte coacervates open a pathway for creating a dual-pH release system in a facile and fast way, which can be applied as main components in active corrosion-protective coatings for Al alloys.

Corrosion inhibition of AA2024-T3 by smart polyelectrolyte coacervates responsive to both acidic and alkaline environments

Previously reported pH-responsive corrosion-protective coatings based on the layer-by-layer assembled polyelectrolytes responded to the pH increase caused by cathodic reactions in corrosion but were less sensitive to the pH decrease in anodic regions. In this study, polyacrylic acid was directly added into polyethylenimine to make polyelectrolyte coacervates capable of releasing SrCrO4 inhibitor at both acidic and alkaline pH. Due to a higher amount of the released SrCrO4 at both low and high pH, AA2024-T3 substrates exhibited better corrosion resistance during cyclic potentiodynamic polarization compared with that in neutral pH chloride solutions. Electrochemical impedance spectroscopy further proved that the corrosion resistance of AA2024-T3 was improved by the application of SrCrO4-embedded polyelectrolyte coacervates. The developed polyelectrolyte coacervates open a pathway for creating a release system for corrosion protection of AA2024-T3 triggered by low and high pH in a facile and fast way.

Synergistic Effect of 3-Amino-1,2,4-triazole-5-thiol and Cerium Chloride on Corrosion Inhibition of AA2024-T3

The inhibition of AA2024-T3 corrosion by the synergistic combination of 3-Amino-1,2,4-triazole-5-thiol (ATAT) and cerium chloride in sodium chloride solution is assessed. Analysis of electrochemical impedance spectroscopy results show improved corrosion inhibition for the inhibitor combination by increased charge transfer resistance. Scanning vibrating electrode technique was utilized for corrosion current monitoring and quantification. X-ray photoelectron spectroscopy and time of flight secondary ion mass spectrometry were utilized to characterize the ATAT/Ce based film and to explain the mechanism of inhibition. The obtained results demonstrate a good potential of the inhibitor combination for improved suppression of corrosion processes.

The Role of Chromium (III) in the Corrosion Inhibition of AA2024-T3 By Trivalent Chromium Process Coatings

High strength aluminum alloys (e.g., AA2024-T3) are widely used as aircraft structural components. The inclusion of two major alloying elements, Cu and Fe, make the metal more susceptible to localized damage in the form of pitting and intergranular corrosion. The susceptibility of the alloy to localized corrosion is due to the fact that galvanic cells form between the Cu- and Fe-rich intermetallic phases, sites that support relatively rapid oxygen reduction reaction kinetics, and the aluminum, which undergoes dissolution. The intermetallic phases are more noble than the surrounding aluminum matrix leading to the localized pitting or dissolution of the aluminum near the intermetallics. Inhibiting this localized corrosion is essential for achieving long performance lifetime of these structural components. Conversion pretreatment coatings are one component of a multilayer coating system that is typically used to protect aerospace aluminum alloys from corrosion. The multi-layer coating system consists of a conversion coating, a primer and an organic topcoat. The focus of current research in our group is on the application of alternate, more environmentally-friendly conversion coatings that serve as suitable replacements for the currently-used chromate conversion coatings (CCC). The corrosion inhibition provided by the multilayer coating system depends on the chemical composition, physical structure and thickness and uniformity of the conversion coating. The need for some level of corrosion inhibition by the conversion coating arises when there is coating breakthrough, in other words a scratch through the coating system that exposes some bare metal. Conversion coating thicknesses are generally in the 50-200 nm range and they provide corrosion inhibition, at least in part, by providing a barrier to oxygen and water/electrolyte accessibility to the metal surface. The trivalent chromium process (TCP) conversion coating is an environmentally-friendly potential replacement for the currently used chromate conversion coating. TCP is regarded as one of the leading drop-in replacements for CCC. Prior work has shown that the TCP coating inhibits corrosion on aluminum alloys, in part, by serving as a barrier layer. A key question with regard to the mechanism of corrosion inhibition is the role of Cr(III) or the transiently formed Cr(VI) that has been shown to form in the coating. We conducted studies using a trivalent chromium conversion coating from Henkel Corp., named Alodine® T5900™ , and a formulation of the same coating devoid of Cr(III). The formation, structure and corrosion inhibition of the coatings was investigated on AA2024-T3. The coating was formed by immersion on a polished, degreased and deoxidized specimen. These conversion coatings are about 100 nm thick when formed by immersion and consist of a biphasic structure with a hydrated zirconia (ZrO2·nH2O) top layer and a fluoroaluminate (e.g., KxAlF3+x) interfacial layer. Electrochemical methods were used to assess the degree of corrosion inhibition. Despite having the same physical structure, the conversion coating containing the Cr(III) exhibited a polarization resistance 10x greater than that for the coating devoid of it. Polarization curves revealed that the TCP coating provided cathodic inhibition. Rotating disk voltammetry was to assess the effect of the coating on the oxygen reduction reaction (ORR) kinetics. The results demonstrated that the TCP coating, as formed, inhibits the ORR. The reduced rate of oxygen reduction is attributed to (i) the formation of a poorly conducting layer on the Cu-rich intermetallics that blocks sites for O2 chemisorption and serves as a barrier to electron transfer and (ii) the formation of diffisusion barrier layer for O2 to the reaction sites.

Corrosion Inhibition of Aluminum Alloy 2024-T3 by Praseodymium Chloride

The mechanism of inhibition of AA2024-T3 (UNS A92024) by praseodymium chloride (PrCl) at varying pH was investigated using electrochemical, microscopic, and spectroscopic techniques. Polarization curves in naturally aerated solutions showed that praseodymium (Pr) provides cathodic inhibition in near-neutral pH solution. Corrosion inhibition of AA2024-T3 by Pr involves the formation of an insoluble film composed of praseodymium carbonate hydroxide (PrCO3·OH) over the intermetallic particles in response to an increase in the pH at the metal/electrolyte interface. As the cathodes on the surface become blocked by a thick oxide, new sites are activated, resulting in the formation of a thick film across the whole surface. The hydroxycarbonate protective layer formed in aerated solution was essential for the protection of the alloy, indicating that carbon dioxide (CO2) played an important role in the inhibition mechanism by Pr. In low and high pH solutions, Pr provided poor inhibition. In the latter case, Pr for...

Synergistic Corrosion Inhibition of AA2024-T3 by Sodium Silicate and Sodium Molybdate

The effect of mixing sodium silicate and sodium molybdate on the corrosion inhibition of AA2024-T3 was investigated using various electrochemical, microscopic and spectroscopic techniques. Strong synergistic behavior was observed when silicate and molybdate were mixed together in solution resulting in much lower threshold concentrations for corrosion inhibition.

Corrosion Inhibition of AA2024-T3 By Sodium Silicate

The mechanism of inhibition of AA2024-T3 by sodium silicate at varying pH was investigated using electrochemical, microscopic and spectroscopic techniques. Polarization curves in naturally aerated solution showed that silicate provides strong anodic inhibition in high alkaline conditions at a threshold concentration of 0.01M. The largest effect was a 1V increase in the breakdown potential at a silicate concentration of 0.025M. The corrosion inhibition mechanism involves the formation of a protective film over the alloy surface by absorption of aluminosilicate anions from solution, as has recently been suggested by others in the literature. At near-neutral pH, silicate partially blocked attack of the intermetallic particles by a precipitation mechanism that resulted in the formation of silica- and silicate- based derivatives. In acidic solution, activation of the aluminum surface promoted the formation of a mixed silica/aluminosilicate film over the surface that was porous in nature, providing very little corrosion protection.

Corrosion Inhibition of AA2024-T3 by Vanadates

The speciation of vanadate solutions and the resulting inhibition of oxygen reduction and corrosion of AA2024-T3 were investigated. 51V NMR is very useful for assessing vanadate speciation. Clear metavanadate solutions contain no decavanadate, which forms whenever the pH was decreased by the addition of acid. Orange decavanadate solutions contain no monovanadate, even when the pH is adjusted to high values. Monovanadate is a potent inhibitor in contrast to decavanadate. Inhibition by monovanadate seems to result from an adsorption mechanism rather than reduction. Monovanadate effectively protects S phase particles. Aging of high-pH decavanadate solutions does not improve the inhibition performance or result in complete depolymerization of the decavanadate.