Corrosion and passive behaviour of aluminium in weakly acid solution

Synthesis of Cyano-Benzylidene Xanthene Synthons Using a Diprotic Brønsted Acid Catalyst, and Their Application as Efficient Inhibitors of Aluminum Corrosion in Alkaline Solutions

Novel cyano-benzylidene xanthene derivatives were synthesized using one-pot and condensation reactions. A diprotic Brønsted acid (i.e., oxalic acid) was used as an effective catalyst for the promotion of the synthesis process of the new starting xanthene–aldehyde compound. Different xanthene concentrations (ca. 0.1–2.0 mM) were applied as corrosion inhibitors to control the alkaline uniform corrosion of aluminum. Measurements were conducted in 1.0 M NaOH solution using Tafel extrapolation and linear polarization resistance (LPR) methods. The investigated xanthenes acted as mixed-type inhibitors that primarily affect the anodic process. Their inhibition efficiency values were enhanced with inhibitor concentration, and varied according to their chemical structures. At a concentration of 2.0 mM, the best-performing studied xanthene derivative recorded maximum inhibition efficiency values of 98.9% (calculated via the Tafel extrapolation method) and 98.4% (estimated via the LPR method). Scanning electron microscopy (SEM) was used to examine the morphology of the corroded and inhibited aluminum surfaces, revealing strong inhibitory action of each studied compound. High-resolution X-ray photoelectron spectroscopy (XPS) profiles validated the inhibitor compounds’ adsorption on the Al surface. Density functional theory (DFT) and Monte Carlo simulations were applied to investigate the distinction of the anticorrosive behavior among the studied xanthenes toward the Al (111) surface. The non-planarity of xanthenes and the presence of the nitrile group were the key players in the adsorption process. A match between the experimental and theoretical findings was evidenced.

Computational and Experimental Evaluation of Inhibition Potential of a New Ecologically Friendly Inhibitor Leaves of Date Palm (Phoenix dactylifera L.) for Aluminium Corrosion in an Acidic Media

PDL (Phoenix dactylifera leaves) is widely spread in Iraq and is known to be rich in phytochemicals as flavonoids, saponins, tannins, glycosides, oils, and lipids. The effect of PDL extract in reducing the corrosion of Aluminium in 1 M HCl solution using a weight loss technique, and computational chemistry calculations were investigated in this study. The study carried out at different temperatures (20, 30, 40, and 50) in the presence of plant extract and the absence of extract. A number of parameters were included to be detected in this study according to the density functional theory (DFT)/P3LYP/6-311G, including the highest occupied molecular orbital EHOMO, the lowest unoccupied molecular orbital ELUMO, energy gap $\Delta E$ , softness $S$ , hardness $\eta$ , dipole moment $\mu$ , electronegativity $\chi$ , electrophilicity $\omega$ , inhibitor-metal interaction energy $∆\psi$ , and electrons transferred fraction $\Delta N$ . Two adsorption isotherms were used to explain inhibitor adsorption behavior. Two adsorption isotherms were used to explain inhibitor adsorption behavior, the Freundlich adsorption isotherm and the Langmuir adsorption isotherm, the Freundlich adsorption isotherm was discovered to be followed by the inhibitor with correlation coefficient values ranging from 0.98 to 0.94 with temperature increased from 20 to 50 degrees Celsius. The adsorption mechanism includes a physical adsorption process. The results showed that with the increment of the inhibitors concentration, there was an improvement of the inhibition efficiency. The most outstanding inhibitor efficiency was 97.7% at 10 mL/L inhibitor concentration.

Role of S2- ions on the microstructure change and the pitting behaviour of aluminum in saline solution

The electrochemical behaviour and the passive film microstructure of aluminum during its exposure to 3.5 wt% NaCl solution in the absence and presence of S²⁻ ions are investigated using potentiodynamic polarization curves, electrochemical impedance spectroscopy measurements, XRD, XRF, SEM and AFM. Electrochemical measurements show that the presence of S²⁻ ions enhances the uniform corrosion of aluminum in NaCl solution, but delay its susceptibility to the pitting corrosion. In addition, EIS analysis illustrate that the formation of more compact and protective passive layer in the presence of S²⁻ ions compared to its rough surface in the absence of S²⁻ ions as evidenced by the lower value of constant phase element (CPE) and higher value of phase shift (N). Cracks, non- homogenous and open large pits with high degree of roughness are clearly observed on the aluminum surface in the absence of S²⁻ ions, compared to oriented grooves, elongated ridges with the accumulation of the corrosion products inside the pits in the presence of S²⁻ ions. The inhibitory effect of S²⁻ ions for the pitting corrosion of aluminum is interpreted on the basis of the change in its microstructure of the passive film in the absence and presence of S²⁻ions.

Adsorption of methylamine on Ni 3 Al(111) and NiAl(110)--a high resolution photoelectron spectroscopy and density functional theory study

Methylamine adsorption on the ordered Ni(3)Al(111) and NiAl(110) surfaces has been investigated by high resolution photoelectron spectroscopy and density functional theory calculations. Methylamine adsorbs molecularly at both surfaces at low temperature (90 K). The experiments show that methylamine interacts with the surface aluminium atoms on both surfaces, resulting in a positive binding energy shift relative to the Al 2p bulk contributions. A shift towards lower binding energy is also observed on NiAl(110) attributed to first and second layer surface Al atoms not bonded to methylamine. According to total energy calculations methylamine binds through its N atom to Al on-top sites on NiAl(110) while the Ni on-top site is found to be slightly preferred over the Al on-top site on Ni(3)Al(111). Calculated adsorbate induced shifts are, however, in good agreement with the experimental values only when methylamine is situated in the Al on-top site on both surfaces. In both cases, a lone pair bonding mechanism is found.