This study investigated the potential of Agave sisalana extract as a novel, sustainable corrosion inhibitor for mild steel in 1 M H₂SO₄. The lipophilic components, such as waxes, terpenoids, and fatty acids, were extracted with ethanol and analyzed using Fourier Transform Infrared Spectroscopy (FTIR). Corrosion behavior was assessed using Potentiodynamic Polarization (PDP) and Electrochemical Impedance Spectroscopy (EIS). The results demonstrated that the extract acts as a mixed-type inhibitor, with a maximum Inhibition Efficiency (IE) of 96.03% at an optimal dose of 750 mg L^⁻¹. The EIS analysis confirmed the formation of a robust protective film, as evidenced by increased charge-transfer resistance and relaxation time constants. Scanning Electron Microscopy (SEM) surface analysis confirmed that a protective adsorbed coating had formed on the steel surface, significantly reducing corrosion damage. According to the current study, Agave sisalana serves as a sustainable, environmentally benign, and promising corrosion inhibitor derived from agro-industrial waste, suitable for extremely acidic environments.

Al₂O₃-based directionally solidified eutectic (DSE) ceramics are recognized as promising candidates for high-temperature structural materials in advanced aeroengines. Nevertheless, their corrosion resistance at elevated temperatures continues to pose a critical challenge, limiting broader application in hot-section components. This study investigates corrosion behavior of RE₃Al₅O₁₂ (REAG)/Al₂O₃ (RE = rare earth) DSE ceramics in water vapor atmosphere (90 H₂O(g) + 10 vol% air(g)) at 1500°C for durations up to 200 h, with focus on the influence of eutectic structure and RE elements in garnet phases via examining three samples (high-entropy (Y_0.2Gd_0.2Ho_0.2Er_0.2Yb_0.2)₃Al₅O₁₂ DSEs fabricated at 10 and 300 mm/h and YAG/Al₂O₃ DSE grown at 10 mm/h). The results indicate that REAG/Al₂O₃ DSE ceramics exhibit excellent water vapor corrosion resistance at 1500°C for up to 200 h, with mass loss values ranging from −0.00757 to −0.00708 mg·cm⁻²·mg⁻¹. During corrosion, Al₂O₃ phase acts as corrosion-susceptible component compared to REAG phase, with corrosion depth showing a nearly linear relationship with the average Al₂O₃ lamellar width. In addition, garnet phases experience slight grain growth, reducing the contact area between water vapor and Al₂O₃ phase; Gd demonstrates the slowest diffusion rate when compared to other RE elements. Despite these changes, all samples maintain their preferred crystallographic orientations, confirming the structural stability of REAG/Al₂O₃ DSEs under water vapor atmosphere at 1500°C.

High-temperature corrosion caused by low-melting-point molten salts known as CMAS poses a critical challenge to hot-section components in gas turbine engines. The screening of CMAS corrosion-resistant RE₂SiO₅ ceramics is crucial for the development of environmental barrier coatings for SiC fiber reinforced SiC composites. Due to varying experimental methods, conditions, and CMAS corrosion evaluation approaches, there has been some controversy regarding the CMAS resistance of RE₂SiO₅ ceramics. To address this issue, we employed a highthroughput multilayer stacking method to eliminate external influences such as experimental conditions. The CMAS resistance of several rare earth silicate ceramics was investigated, which revealed the influence of rare earth elements on CMAS corrosion. It was found that the smaller the rare earth ionic radius, the less corrosion product formed. Additionally, Er₂SiO₅ exhibited the best CMAS resistance due to the shallowest penetration depth of CMAS. The results indicate that the evaluation of CMAS corrosion resistance of RE₂SiO₅ ceramics requires a comprehensive consideration of the formation ability of corrosion products, dissolution of RE₂SiO₅, and the penetration of CMAS.

This study explored the prevention of mild steel (MS) corrosion in sulfuric acid through deployment of N, Ndibutylaniline (NNDBA) as an organic inhibitor. The inhibition efficacy was meticulously scrutinized using a blend of qualitative and quantitative methodologies. The gravimetric method was executed across a spectrum of NNDBA concentrations (10^-1M-10^-7M ) and temperatures, 298 K-328 K (with 10 K increments), facilitating an intricate kinetic and thermodynamic exploration of the inhibition mechanism. Adsorption isotherm analyses affirmed NNDBA's adherence to Langmuir's model, signifying a monolayer adsorption paradigm. The adsorption process was found to be spontaneous and thermodynamically favorable, predominantly governed by physisorption. Empirical data delineated an inverse relationship between temperature and inhibition efficiency, whereas an augmentation in NNDBA concentration bolstered corrosion resistance. Potentiodynamic Polarisation (PDP) confirmed that NNDBA is a mixed-type inhibitor with a maximum efficiency of 92.4%. Electrochemical Impedance Spectroscopy (EIS) measurements revealed a marked decrement in the double-layer capacitance at the Fe/H₂SO₄ interface, corroborating inhibitor adsorption. Notably, the lower value of the phase shift exponent n for NNDBA suggests increased surface heterogeneity due to inhibitor film formation. Scanning Electron Microscopy (SEM-2D) and Atomic Force Microscopy (AFM-3D) unveiled distinct morphological alterations indicative of surface passivation. Density functional theory (DFT) calculations provided insights into the electronic structure of NNDBA, revealing a highly negative E_HOMO , low E_LUMO , and a small ΔE(5.24eV), all suggesting strong reactivity and the formation of a stable metal-inhibitor complex. The mechanistic pathway and spatial orientation of the interaction between the NNDBA molecule and MS surface were explored through molecular dynamics simulation to gain insights into its inhibitory behavior. Thus, the theoretical insights harmonize with experimental findings, substantiating its efficacy as a potent corrosion mitigant.

In order to get a comprehensive understanding of the corrosion behaviour of mild steel (110) with alanine, arginine, cysteine, and tyrosine in gas and aqueous phases, a systematic theoretical study using MC simulation was conducted in the current investigation. Stronger interfacial spontaneous adsorption of amino acid molecules across the Fe (110) surface in the investigated environment is made possible by the more negative adsorption energy values found in the MC simulation. Effectively repelling the corrosive particles from the substrate and delaying their aggregation are the capabilities of four amino acids. The results of the MC simulation also show that, in order to stop corrosion, amino acid molecules replace any other ions or solvent water that had previously been adsorbed on the metal surface. The trend of tyrosine > cysteine > alanine > arginine is shown by the protection capacity derived from the MC simulation. Furthermore, the DFT studies demonstrate that, charge transfer takes place within the molecule based on the calculated E-HOMO and E-LUMO energies. When adsorbed onto a metal surface, heteroatoms like nitrogen, oxygen, and sulphur in an amino acid structure provide the stronger inhibition. The decreased HOMO-LUMO gap, indicating improved electronic contact with the Fe (110) surface. A greater reactivity and potential for electron transfer are suggested by the EHOMO and ELUMO values (EHOMO -19.71 eV for alanine, -16.83 for cysteine, -10.73 for arginine and -16.80 for tyrosine) and (ELUMO EHOMO -10.81 eV for alanine, -9.34 for cysteine, -2.69 for arginine and -9.06 for tyrosine) which are advantageous for adsorption onto the Fe ( 110 ) surface. Current study finds that, alanine, arginine, cysteine and tyrosine were emerging as a novel and effective and sustainable corrosion resistance agent for acid pickling and cleaning procedures. These outcomes may lead to the development of more and large-scale green inhibitors and a better understanding of their mechanisms for eco-friendly industrial processes.

Thermal and environmental barrier coatings play a crucial role in protecting high-temperature structural components in gas turbine engines. As turbine inlet temperatures continue to rise, corrosion challenges posed by dust, volcanic ash, and other particulate matter—collectively known as CMAS—have become increasingly severe. Understanding the reaction mechanisms between CMAS and these coatings, identifying the key factors influencing CMAS corrosion, and developing methods to inhibit CMAS infiltration are essential for advancing high-performance gas turbine engines. This review examines the origins of CMAS corrosion and summarizes recent research on CMAS corrosion mechanisms in thermal and environmental barrier coating materials. Additionally, the role of rare earth elements in CMAS corrosion and various strategies to mitigate CMAS effects are discussed. Finally, the review highlights potential directions for future research.

Improving the corrosion resistance of environmental barrier coatings (EBCs) to molten calcium-magnesium-aluminosilicate (CMAS) salt is an urgent requirement for aeroengine blades. In this work, a novel high-entropy (Ho_0.2Er_0.2Tm_0.2Yb_0.2Lu_0.2)₂Si₂O₇ ((5RE_0.2)₂Si₂O₇) environmental barrier coating material was developed, and molten CMAS corrosion resistance of (5RE_0.2)₂Si₂O₇) was systematically investigated at 1500 °C. The prepared (5RE_0.2)₂Si₂O₇ ceramic possesses a single and stable β-phase structure with high-temperature stability from room temperature to 1500 ℃. The thermal conductivity of (5RE_0.2)₂Si₂O₇ ranges from 1.46 to 3.49 W·m⁻¹·K^-1 at room temperature to 1500 ℃. A rapid reaction of (5RE_0.2)₂Si₂O₇ with molten CMAS produced Ca₂RE₈(SiO₄)₆O₂ apatite at 1500 ℃. The reaction layer thickness was only 95.9±8.6 μm which effectively inhibited the infiltration and diffusion of molten CMAS salt. In contrast, Yb₂Si₂O₇ ceramic, when exposed to molten CMAS at 1500 ℃, showed no reaction. Instead, the molten CMAS salt penetrated into the interior of Yb₂Si₂O₇ along grain boundaries and voids, forming bubble cracking and ultimately, structural degradation. These results suggest that the high-entropy (5RE_0.2)₂Si₂O₇ ceramic material is a potential candidate for next-generation EBC with excellent resistance to CMAS corrosion.

The mitigation of aluminum corrosion in HCl is crucial for economic, safety, and environmental considerations. The influence of Trimethoprim-Sulfamethoxazole (TMP-SMX) on the corrosion of aluminum in 1 M HCl was investigated through both electrochemical and computational methodologies. A notable difference in the open circuit potential values between the blank HCl and the inhibited system was recorded, indicating that TMP-SMX affects the electrochemical behavior of aluminum in 1 M HCl. The charge transfer resistance increased from 220 Ω cm2 without TMP-SMX to 610 Ω cm2 when 0.4 g/L of TMP-SMX was present, suggesting the establishment of a shielding TMP-SMX film on aluminium exterior. The current density exhibited a substantial decrease in the presence of TMP-SMX. The alteration in corrosion potential upon the incorporation of TMP-SMX remained below 85 mV, which suggests that TMP-SMX simultaneously retards anodic metal deterioration and cathodic hydrogen evolution. Computational simulation revealed that TMX and SMX maintain nearly parallel orientations with respect to the aluminum surface, suggesting enhanced surface coverage and interactions through heteroatoms and π-electron systems. ∆G⁰ values were negative, signifying that TMP/SMX spontaneously adhered to aluminum. Corrosion rate increased with rising temperature, but decreased with higher inhibitor concentrations. TMP-SMX has the potential to function as an environmentally friendly corrosion inhibitor for aluminium in HCl.