High effective organic corrosion inhibitors for 2024 aluminium alloy

In-Depth Insight into Corrosion Inhibition Performance of Sweet Potato Leaf Extract as a Green and Efficient Inhibitor for 6N01 Al Alloy in the Seawater: Experimental and Theoretical Perspectives

Corrosion protection of metal has become an important and urgent topic, which requires the development of an inexpensive, environmentally friendly, and highly efficient corrosion inhibitor. Herein, a sweet potato leaf extract (SPL) was obtained by a simple water-based extraction method and then as a green corrosion inhibitor for 6N01 Al alloy in the seawater was well investigated by the weight loss method and various electrochemical tests. Fourier transform infrared (FT-IR) and ultraviolet-visible (UV-vis) spectroscopies were carried out to investigate the compositions of SPL. The findings from the potentiodynamic polarization (PDP) curves suggest that SPL functions as a typical mixed-type corrosion inhibitor. Notably, the maximum corrosion inhibition efficiency reaches 94.6% following a 36 h immersion period at 25 °C. The adsorption behavior of SPL on the Al alloy surface belongs to the Langmuir adsorption isotherm. The Gibbs free energy value illustrates that the adsorption of SPL contains both physisorption and chemisorption. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) indicate that SPL is firmly attached to the Al alloy surface by making a protective layer, which can effectively inhibit the corrosion of the Al alloy in the seawater. Furthermore, quantum chemical calculations were applied to validate the chemical adsorption and elucidate the relationship between the electronic structure of the active components in SPL and their effectiveness in corrosion inhibition.

Potential of rare-earth compounds as anticorrosion pigment for protection of aerospace AA2198-T851 alloy

In this study, the anticorrosion potential of carboxylic compounds; Lanthanum 4-hydroxycinnamate La(4OHCin)₃, Cerium 4-hydroxycinnamate Ce(4OHCin)₃ and Praseodymium 4-hydroxycinnamate Pr(4OHCin)₃ for the protection of Al-Cu-Li alloy was investigated in 3.5% NaCl solution using electrochemical tests (EIS and PDP), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The findings achieved show a very good correlation between electrochemical responses and surface morphologies of the exposed alloy, indicating a modification of the surface by precipitation of the inhibitor species, leading to effective protection against corrosion. At optimum concentration 200 ppm, the trend of inhibition efficiency η (%) increases in the order Ce(4OHCin)₃ 93.35% > Pr(4OHCin)₃ 85.34% > La(4OHCin)₃ 82.25%. XPS complemented the findings by detecting and providing information about the oxidation states of the protective species.

Heteropolysaccharides in sustainable corrosion inhibition: 4E (Energy, Economy, Ecology, and Effectivity) dimensions

Carbohydrate polymers (polysaccharides) and their derivatives are widely utilized in sustainable corrosion inhibition (SCI) because of their various fascinating properties including multiple adsorption sites, high solubility and high efficiency. Contrary to traditional synthetic polymer-based corrosion inhibitors, polysaccharides are related to the 4E dimension, which stands for Energy, Economy, Ecology, and Effectivity. Furthermore, they are relatively more environmentally benign, biodegradable, and non-bioaccumulative. The current review describes the SCI features of various heteropolysaccharides, including gum Arabic (GA), glycosaminoglycans (chondroitin-4-sulfate (CS), hyaluronic acid (HA), heparin, etc.), pectin, alginates, and agar for the first time. They demonstrate impressive anticorrosive activity for different metals and alloys in a variety of corrosive electrolytes. Through their adsorption at the metal/electrolyte interface, heteropolysaccharides function by producing a corrosion-protective film. In general, their adsorption follows the Langmuir isotherm model. In their molecular structures, heteropolysaccharides contain several polar functional groups like -OH, -NH₂, -COCH₃, -CH₂OH, cyclic and bridging O, -CH₂SO₃H, -SO₃OH, -COOH, -NHCOCH₃, -OHOR, etc. that serve as adsorption centers when they bind to metallic surfaces.

Insight at the atomic scale of corrosion inhibition: DFT study of 8-hydroxyquinoline on oxidized aluminum surfaces

8-Hydroxyquinoline (8-HQ) is a promising organic molecule for the corrosion protection of aluminum and its alloys in the replacement of chromate salts. On the aluminum surface, the presence of an oxide layer naturally formed can influence the inhibition efficiency which depends on molecule-surface interactions. In the present study, we performed quantum chemical calculations on native 8-HQ, tautomer and 8-Q (deprotonated, H-abstracted or radical) molecules, adsorbed on an oxidized aluminum surface (γ-Al₂O₃(111)/Al(111)). All species have the ability to interact strongly with the oxidized aluminum surface and can form stable and dense organic films. The bonding strength of different species of 8-HQ on oxidized aluminum surfaces is more favorable for 8-Q and tautomer species than for the native 8-HQ molecule. On the surface, the native 8-HQ molecule is physisorbed, forming H-bonds, in contrast to the tautomer and 8-Q species that show the predominance of chemisorption modes, involving both H-bonds and covalent bonds at the molecule/substrate interface. The dispersion energy significantly contributes to the adsorption mechanism and increases with increasing molecular surface coverage, due to attractive molecule-molecule interactions. Regardless of surface coverage and considered reaction mechanisms, the 8-Q species is able to enhance the stability of all aluminum sites, and thus to slow down the anodic reaction. In contrast, the native molecule and the tautomeric form have no significant effect or even weakened the stability of aluminum surface atoms.

Chromate-Free Corrosion Protection Strategies for Magnesium Alloys-A Review: Part III-Corrosion Inhibitors and Combining Them with Other Protection Strategies

Owing to the unique active corrosion protection characteristic of hexavalent chromium-based systems, they have been projected to be highly effective solutions against the corrosion of many engineering metals. However, hexavalent chromium, rendered a highly toxic and carcinogenic substance, is being phased out of industrial applications. Thus, over the past few years, extensive and concerted efforts have been made to develop environmentally friendly alternative technologies with comparable or better corrosion protection performance to that of hexavalent chromium-based technologies. The introduction of corrosion inhibitors to a coating system on magnesium surface is a cost-effective approach not only for improving the overall corrosion protection performance, but also for imparting active inhibition during the service life of the magnesium part. Therefore, in an attempt to resemble the unique active corrosion protection characteristic of the hexavalent chromium-based systems, the incorporation of inhibitors to barrier coatings on magnesium alloys has been extensively investigated. In Part III of the Review, several types of corrosion inhibitors for magnesium and its alloys are reviewed. A discussion of the state-of-the-art inhibitor systems, such as iron-binding inhibitors and inhibitor mixtures, is presented, and perspective directions of research are outlined, including in silico or computational screening of corrosion inhibitors. Finally, the combination of corrosion inhibitors with other corrosion protection strategies is reviewed. Several reported highly protective coatings with active inhibition capabilities stemming from the on-demand activation of incorporated inhibitors can be considered a promising replacement for hexavalent chromium-based technologies, as long as their deployment is adequately addressed.

Evaluation of Corrosion Inhibition of Essential Oil-Based Inhibitors on Aluminum Alloys

There is a high demand for eco-friendly, effective, and high-performance corrosion inhibitors for industrial applications. Thus, the corrosion property of aluminum alloys was studied in essential oil-containing sodium chloride solution at various concentrations. Potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), surface tests, and weight loss analysis were used to study the corrosion inhibition mechanism of the essential oil. The essential oil showed the highest inhibition efficiency of 97.01% at 1000 ppm. A high efficiency of 96.03% was achieved even after 168 h of exposure. The potentiodynamic polarization test showed that the essential oil is a mixed-type inhibitor. EIS results show better adsorption of the oil on the surface of the aluminum at increased inhibitor concentrations. The Langmuir's adsorption isotherm model was found to describe the adsorption behavior. The surface morphology of the uninhibited and inhibited specimens examined by a scanning electron microscope equipped with an energy-dispersive X-ray spectroscope confirmed the protective film of the inhibitor molecules on the aluminum surface.

Evaluation of Tannins as Potential Green Corrosion Inhibitors of Aluminium Alloy Used in Aeronautical Industry

In this work some organic natural products were studied, namely tannic acid, gallic acid, mimosa tannin and chestnut tannin, as potential green corrosion inhibitors of the aluminium alloy AA2024-T3. The anodizing treatment was performed in a solution of the referred organic compounds in diluted sulfuric acid. The electrochemical impedance spectroscopy and the potentiodynamic polarization were performed to assess sealing quality and corrosion protection granted by the anodic films. To understand the green inhibitors; interaction with the metal surface, FTIR spectra of anodizing and anodizing and sealed samples of AA2023-T3 were recorded, and the shifts in the position of the major bands confirmed that the green inhibitor interacts with the metal surface. Images of the morphology of the coatings were provided by Scanning Electron Microscopy. From the results obtained through the various techniques that were used to carry out this study it is possible to conclude that the formed anodic films can be a good contribution for the prevention of corrosion in the aluminium alloy AA2024-T3.

Evaluation of Corrosion Inhibition Efficiency of Aluminum Alloy 2024 by Diaminostilbene and Azobenzene Schiff Bases in 1 M Hydrochloric Acid

The Schiff base compounds N,N ${}^{\prime }$ -bis(salicylidine)-4,4 ${}^{\prime }$ –diaminostilbene(SDS) and N,N ${}^{\prime }$ -bis(salicylidine)-4,4 ${}^{\prime }$ -diamino azobenzene(SDA) were synthesized, and their molecular structure was determined by FT-IR and 1H NMR. The corrosion inhibitions of Schiff base compounds on aluminum alloy 2024 in 1 M hydrochloric acid were evaluated by potentiodynamic polarization, impedance techniques, weight loss method, and scanning electron microscopic technique. The potentiodynamic polarization (PDP) studies revealed that SDS and SDA compounds acted predominantly as cathodic inhibitors. The electrochemical impedance spectroscopic (EIS) parameters confirmed the adsorption of SDS and SDA molecules over the surface of aluminum alloy 2024 alloy by forming an inhibitive layer. The weight loss studies showed that the inhibition efficiency of these compounds increases directly with concentration and decreases with an increase in solution temperature and immersion time. The thermodynamic parameters were calculated to investigate the mechanism of corrosion inhibition. The SDA was found to be more effective than SDS and followed the Langmuir adsorption isotherm model. The scanning electron microscopy (SEM) results revealed that the deterioration of the alloy surface is minimal in the presence of an inhibitor. Both Schiff base molecules exhibited superior corrosion inhibition for aluminum alloy 2024 alloy in HCl medium.

Coumarin as a green inhibitor of chloride-induced aluminum corrosion: theoretical calculation and experimental exploration

In the present work, the adsorption mechanism and corrosion inhibition effect of coumarin as a green inhibitor was characterized. Quantum chemical calculation and molecular dynamics simulation of the coumarin molecule were performed to get insight into the adsorption model by assessing the frontier orbital parameters and adsorption configuration. The theoretical calculation disclosed that coumarin exhibited a higher adsorption reactivity in the water phase than that in the gas phase, and the C[double bond, length as m-dash]O structure in coumarin was the most favorable site for adsorption occurring. Coumarin could adsorb spontaneously on an aluminum surface in a parallel manner, where electron donation occurred from the aluminum surface to the inhibitor. Additionally, the experimental investigation determined that coumarin decreased the aluminum dissolution by suppressing both the anodic and cathodic reactions. The optimal coumarin concentration of 0.5 wt% resulted in a maximum inhibition efficiency (89.6%), but coumarin at a higher concentration would lead to the competitive and unstable adsorption of inhibitor molecules, thus decreasing the inhibition effect. Moreover, surface chemical characterization confirmed the formation of Al-coumarin complexes, which was in accordance with the theoretical calculation.

Hybrid Organic-Inorganic Materials on Metallic Surfaces: Fabrication and Electrochemical Performance

In recent years, hybrid organic-inorganic (HOI) materials have attracted massive attention as they combine the unique properties of organic and inorganic compounds. In this review, we focus on the formation of HOI materials and their electrochemical performance that can be controlled by microstructural design depending upon their chemical composition. This overview outlines the recent strategies of preparing HOI materials on metallic surface via wet-electrochemical systems, such as plasma electrolysis (PE) and dip chemical coating (DCC). The corresponding electrochemical behavior for short and long term exposures is also summarized.

Topological Analysis of Hydroxyquinoline Derivatives Interacting with Aluminum Cations or with an Al(111) Surface

The reactivity of hydroxyquinoline derivatives (native molecules (Hq) and modified species (HqX, X = Br, SO₃H, or SO₃^-)) is investigated either (i) with aluminum cations for the formation of chelates or (ii) with aluminum surfaces for their adsorption properties, in the framework of the dispersion-corrected Density Functional Theory (DFT-D). It is shown that the substituent X has no influence on the complexation to the aluminum cation of the deprotonated active form, i.e., the one exhibiting a phenolate moiety and referred to as q^- for the native Hq and qX^n- (n = 1 or 2) for its derivatives. The formation energies of the Alq₃ and Al(qX)₃ complexes, taking values of -60.87 ± 3.10 eV in vacuum and -24.30 ± 0.29 eV in water, are indicative of a strong chelating affinity of the q^- and qX^n- (n = 1 or 2) anions for the aluminum cations. ELF and QTAIM topological analyses on these complexes evidence that the bonding of the deprotonated species with the Al³⁺ ion is ionic with a very weak covalence degree. The para or ortho substituent X of the phenolate moiety of the qX^n- (n = 1 or 2) derivatives modifies the electronic structure only locally and thus does not influence their O- or N-coordinating properties. The adsorption properties of the latter on an Al(111) surface have also been studied within periodic DFT-D calculations. The adsorbed species are strongly interacting with the Al(111) surface, as shown by the value of the adsorption energy of -3.69 ± 0.21 eV for the most stable geometries. Various adsorption modes of the q^- and qX^n- (n = 1 or 2) derivatives are characterized on the Al surface, depending on stabilizing or destabilizing interactions with the substituents X. On the basis of QTAIM descriptors, the bonding of the hydroxyquinoline species on the aluminum surface is characterized as ionic with a weak covalent character.

Hyperbranched molecules having multiple functional groups as effective corrosion inhibitors for Al alloys in aqueous NaCl

Hyperbranched molecules are a kind of promising materials due to their unique structures. In this work, two hyperbranched molecules (GON and GOH) are used as effective inhibitors for Al alloys in NaCl solution. Their inhibitive performances are evaluated by electrochemical measurements and surface characterization. The results indicate that inhibition performances of GON and GOH are closely related to the concentrations, influenced by the combination of steric hindrance and bonding effects. At relatively low concentrations (0.03-0.10 mM), GON displays a more pronounced ability to inhibit corrosion than GOH, owing to more anchoring functional groups. Oppositely, GOH has good inhibition performance at higher concentrations (0.50-1.00 mM). The interaction between the Al electrode and GOH results in the formation of a more condenser protective film than GON at high concentrations. In addition, the adsorption mechanism of two hyperbranched molecules is revealed by theoretical calculations.

Corrosion Inhibition at Scribed Locations in Coated AA2024-T3 by Cerium- and DMTD-Loaded Natural Silica Microparticles under Continuous Immersion and Wet/Dry Cyclic Exposure

Earlier studies on cerium-loaded naturally occurring silica microparticles (i.e., diatomaceous earth) demonstrated the potential to efficiently protect small scratches in epoxy-coated AA2024-T3 panels during relatively short immersion times. The current work investigates the potential of such inhibitor-loaded microparticles to protect wide and deep scribes (up to 1 mm wide) in long-time immersion testing and during cyclic (wet/dry) conditions. For this, cerium nitrate and 2,5-dimercaptothiadiazole (DMTD) were used as inorganic and organic corrosion inhibitors. The corrosion protection was evaluated using a hyphenated real-time optics/electrochemistry method and two individual local techniques measuring oxygen concentration and electrochemical impedance (LEIM) inside the scribe. SEM/EDS was used to analyze the samples after exposure. The results show significant levels of corrosion protection at damaged locations at low cerium concentrations (3.7 wt % Ce³⁺ relative to the total coating mass) during 30 days of immersion in salt solution. However, for a given scribe geometry, the protection was found to be dependent on the electrolyte volume with larger electrolyte/exposed metal ratios leading to short protection time. A partial replacement of the Ce³⁺ by DMTD in the microcarriers resulted in a higher degree of passivation than when DMTD was used alone. Wet/dry cyclic exposure tests showed that cyclic conditions can increase the buildup of stable inhibitor-containing layers in the case of cerium-loaded silica microparticles. This underlines the need for more research using wet/dry exposure conditions.

Cerium Dioxide Nanoparticles as Smart Carriers for Self-Healing Coatings

The utilization of self-healing cerium dioxide nanoparticles (CeO2), modified with organic corrosion inhibitors (dodecylamine (DDA) and n-methylthiourea (NMTU)), in epoxy coating is an efficient strategy for enhancing the protection of the epoxy coating and increasing its lifetime. Fourier transform infrared (FTIR) spectroscopy analysis was used to confirm the loading and presence of inhibitors in the nanoparticles. Thermal gravimetric analysis (TGA) measurement studies revealed the amount of 25% and 29.75% w/w for NMTU and DDA in the nanoparticles, respectively. The pH sensitive and self-release behavior of modified CeO2 nanoparticles is confirmed through UV-vis spectroscopy and Zeta potential. It was observed, through scanning electron microscopy (SEM), that a protective layer had been formed on the defect site separating the steel surface from the external environment and healed the artificially created scratch. This protective film played a vital role in the corrosion inhibition of steel by preventing the aggressiveness of Cl- in the solution. Electrochemical impedance spectroscopy (EIS) measurements exhibited the exceptional corrosion inhibition efficiency, reaching 99.8% and 95.7% for the modified coating with DDA and NMTU, respectively, after five days of immersion time.

Acid-cleavable polymers for simultaneous fast and slow release of functional molecules

Hydrophobic copolymers are designed to respond to acid stimuli for both simultaneous rapid and sustained release of multiple cargos.

Self-reporting of payload release in polymer coatings based on the inner filter effect

New polymeric nanoparticle sensors are developed for monitoring the release of non-fluorescent payloads in coatings by the naked eye.

8-Hydroxyquinoline complexes (Alq3) on Al(111): atomic scale structure, energetics and charge distribution

8-Hydroxyquinoline (8Hq) is known to efficiently inhibit the corrosion of aluminium by forming metal–organic layers (8Hq forms complexes with aluminium atoms).

Corrosion protection mechanism of Ce4+/organic inhibitor for AA2024 in 3.5% NaCl

Cerium is a rare earth element that has been widely proposed for the corrosion protection of aluminium alloys (AA). Both cerium salts, Ce³⁺ and Ce⁴⁺, have been used in combination with other compounds to offer synergistic inhibition, however, the inhibitive corrosion mechanism when using Ce⁴⁺ with organic compounds is still not clear. In this study, the synergistic inhibition effect of Ce⁴⁺ and melamine (M) on the corrosion of aluminium alloy 2024 (AA2024) in 3.5% NaCl solution was investigated. Potentiodynamic Polarization (PDP) and Electrochemical Impedance Spectroscopy (EIS) techniques were used to study the synergistic effect of different Ce⁴⁺/M ratios on the corrosion behaviour of AA2024. The PDP study showed that a combination of 50% Ce⁴⁺ and 50% M leads to the lowest corrosion rates, both acting as cathodic inhibitors. Both PDP and EIS results indicated that M or Ce⁴⁺ in isolation did not offer effective corrosion protection, while the combination of M and Ce⁴⁺ significantly enhances the corrosion protection with a synergism parameter equal to 3.5. SEM and EDX observations confirm the findings from the electrochemical techniques. XPS was used to investigate the mechanism of protection, revealing that the reduction of Ce⁴⁺ to Ce³⁺ occurs during protection of AA2024. A new mechanism of corrosion synergistic inhibition by Ce⁴⁺ and organic compounds is postulated where the role of the organic compounds is to enhance the reduction of Ce⁴⁺.

Proposed corrosion protection mechanism of Ce⁴⁺/ organic inhibitor for AA2024.

Chemical Profiling of Bulk Alloys Using Micro-Electrochemical Probe Mass Spectrometry

Micro-electrochemical probe mass spectrometry (μECP-MS) is demonstrated as a method for the direct profiling of chemical composition of bulk alloy samples without tedious sample pretreatment. The spatial distribution of Zn and Cu components of a Cu/Zn alloy sample was successively identified by scanning the electrolysis potential from -0.6 V to 0.6 V. The lateral resolution of alloy chemical profiling was ≤10 μm, and the depth resolution was ≤0.5 nm. Besides metal components, the method also allows the simultaneous detection of organic molecules on the sample surface. The limit of detection for Rhodamine B, Zn, and Cu depositions was 4.47, 9.58, and 24.25 ag per μm², respectively. The method is particularly useful for high-throughput (<2 min per single run) quality monitoring of industrial parts and conductive materials of irregular geometries, such as alloy, microchips, solder side, etc.