Adsorption Of Inhibitor Research Articles

Utilization of green inhibitors as a sustainable corrosion control method for steel in petrochemical industries: A review

Infrastructure upgrades in the energy sector are encouraged to satisfy the expanding world’s energy needs, including innovation, consumption, production, and transportation. Thus, steel has been an extensively used construction material, particularly for pipelines and oil wells. However, in their application, every step of the production cycle results in the corrosion of metal parts. One of the simplest and most active ways to inhibit steel from corroding, especially in acidic situations, is to use a corrosion inhibitor. Synthetic organic compounds have been used successfully as corrosion inhibitors in the gas and oil industry. However, their use is today restricted and controlled due to their toxicity, environmental harm, and growing concern about the preservation of ecosystems. This has necessitated the present trend of searching for and developing green inhibitors that are environmentally benign, non-toxic, biodegradable, and low in cost. Corrosion inhibitor develops a shielding layer on the metal surface. Corrosion is avoided by a thin coating that has been adsorbed on the metal surface, which keeps the metal isolated from its surroundings. Several researchers have reported on the success of green inhibitors for steel corrosion protection, particularly in acidic environments. However, the use of green inhibitors still leaves several questions about inhibitor formulation, content, and adsorption mechanisms to be answered. Therefore, based on provided experimental results and an explanation of their inhibitory action, the use of green inhibitors (especially organic inhibitors) for the prevention of pipeline steel corrosion in various grades is studied in this review. Both the identified drawback and the projected future trend have also been highlighted.

Comparative study on inhibitory performance of an ionic liquid on corrosion of 6061 Al‐10(vol.%) SiC(P) composite material and base alloy

AbstractInhibitive performance of 1,3 dimethyl imidazolium dimethyl phosphate (DIDP) towards the corrosion of 6061‐Al (10 vol.%) SiC(P) composite (Al‐CM) and base alloy in 0.1 M HCl medium was studied using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques at different temperatures. Optimization of inhibitor concentration was done to get maximum inhibition efficiency. Thermodynamic parameters were calculated by fitting the results into a suitable adsorption isotherm. Scanning electron microscope (SEM), energy‐dispersive X‐ray (EDX), and atomic force microscope (AFM) analyses were performed to understand surface morphology, elemental mapping, and surface roughness before and after the addition of DIDP. UV–visible and X‐ray diffraction (XRD) tests were performed to confirm the adsorption of inhibitor on the surfaces of materials. Studies revealed an increased rate of corrosion for Al‐CM than for the base alloy. The maximum inhibition efficiency for the base alloy was found to be 80.48% for the addition of 1000 ppm, and for Al‐CM, it was found to be 87.38% for the addition of 1400 ppm at 303 K. As the temperature increased, the inhibition efficiency decreased. The inhibitor was adsorbed physically on the surface of the metal by obeying the Freundlich adsorption isotherm. Surface studies confirmed the adsorption of DIDP on the surfaces of both Al‐CM and the base alloy.

Preparation of zwitterionic ionic surfactants-based sulphonyl for steel protections: Experimental and theoretical insights

Abstract Designating an organic inhibitor with a specific chemical structure that actively participates in steel protection by increasing adsorption on the steel surface. Based on that, we synthesized three zwitterionic surfactants based on azomethine with different hydrophobic chain lengths labeled ZWSO, ZWSD, and ZWSH. The presence of azomethine group, electrons, and heteroatoms in the zwitterionic surfactant’s amphipathic structure helped to improve C-steel protection. Their inhibitory activity toward steel corrosion was investigated utilizing electrochemical impedance spectroscopy (EIS), gravimetrical, and potentiodynamic polarization techniques. Importantly, the surfactant tail influenced corrosion inhibition performance; as surfactant tail length increased, so did inhibition efficiency due to increased adsorption affinity. The inhibition efficiencies of ZWSO, ZWSD, and ZWSH are 87.15, 89.82, and 91.36%, respectively. Tafel data clarified that ZWSO, ZWSD, and ZWSH inhibitors behave as mixed-type inhibitors following the modified Langmuir isotherm. The inhibitors can adsorb physiochemically on the steel surface with ∆G ads ranges from −38.48 to −44.6 kJ mol−1. The SEM confirms that the morphology of C-steel becomes smoother because of inhibitor adsorption. The DFT and MCs output data supported the experimental performance of the tested ZWSO, ZWSD, and ZWSH inhibitors and especially their dependence on surfactant tail length.

Experimental investigation of new compound adsorption on carbon steel in 1M HCl

The effect of new compounds named, 6,6'-(((2,2-dimethylpropane-1,3-diyl)bis(azanediyl))bis(methylene))bis(2- methoxyphenol) (RSH) on the corrosion inhibiting of ST- 37 low carbon steel in 1.0 M HCl has been studied. The inhibitor effects on the corrosion behaviour of the samples have been determined at three different concentrations, 0.5, 1.0, 1.5 and 2.0 mg/L. Weight loss, polarization curves, AC impedance measurements and Atomic Force Microscopy (AFM) have been utilized to study the corrosion behaviour of carbon steel in corrosive environment in the presence and absence of new ligand. Results show that the inhibition occurs through adsorption of the inhibitors molecules on the metal surface. The inhibition efficiency was found to increase with increasing inhibitor’s concentration. Polarization data indicated that this compounds act as mixed-type inhibitors. The corrosion efficiency of RSH at an optimal concentration of 2mg/L is 86. The adsorption of inhibitors follows the Langmuir isotherm. The values of free energy of adsorption in the presence of the corrosion inhibitor are around -32 KJmol-1, which indicate chemiosorption of the molecules. Powerful Atomic Force microscopy is used for the surface morphology studies.

Evaluation of Trimethoprim Drug as a Green Corrosion Inhibitor for Mild Steel in 1.0 M Sulfuric Acid

The mitigation of mild steel corrosion in 1.0 M H2SO4 solution by trimethoprim drug as a green and commercially available inhibitor was studied at room temperature using weight loss, open circuit potential, and potentiodynamic polarization techniques. The results showed that the investigated compound's inhibition efficiency depended on the concentration and nature of the inhibitor. The inhibition efficiency was found to increase with the concentration of the inhibitor. The polarization result indicated that the compound behaved as mix type inhibitor. The inhibition is assumed to occur via physical adsorption of inhibitor on the metal surface, which obeyed Langmuir adsorption isotherm. The scanning electron microscope (SEM) and Energy-dispersive X-ray spectroscopy (EDX) results confirmed the formation of a protective layer on the mild steel surface.

Evaluation of Anti-corrosive Efficacy of Prosopis Cineraria Extract on the Nitric Acid Corrosion of Copper

Anti-corrosive propensity of Prosopis cineraria extract on the corrosion behavior of copper (Cu) in nitric acid (HNO3) medium was investigated by applying gravimetric technique. Corrosion inhibition efficiency of Prosopis cineraria was observed to enhance with increasing concentration of extract and reduce with elevation in temperature. The inhibitor underwent physisorption on the Cu metal surface. Adsorption characteristics were approximated by Langmuir adsorption isotherm. Highest inhibition efficiency (η%) 86.12 % was obtained at 303±1 K in fruit extract. It was observed that the extract acts as a benign potential corrosion inhibitor for Cu corrosion in 1.0 M HNO3 acid solution. Results revealed that existence of Prosopis cineraria extract enhances the energy of activation (Ea) of corrosion reaction. Adsorption parameters such as kinetic and thermodynamic [Gibbs free energy change (ΔG0ads) and adsorption equilibrium constant (Kads)] of adsorption process were determined from experimental data. These parameters show a strong interaction between surface of copper metal and inhibitor extract. The inhibitor adsorption process on surface of copper was found to be physical, exothermic and spontaneous. The surface morphology and characterization of copper was done by applying scanning electron microscope (SEM).

Sodium Succinate as a Corrosion Inhibitor for Carbon Steel Rebars in Simulated Concrete Pore Solution.

The inhibiting performance of sodium succinate (Na2C4H4O4) was evaluated as an organic environmentally friendly corrosion inhibitor for carbon steel rebars in 0.6 M Cl- simulated concrete pore solution. Potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) measurements were utilized to evaluate the inhibitor performance at different temperatures and concentrations. The investigated corrosion inhibitor showed strong corrosion inhibition performance as it adsorbs on the surface of the rebar, creating a protective adsorption film. According to PDP, the inhibitor is classified as a mixed-type inhibitor with an inhibitor efficiency of 77, 69, 59, and 54% for 25, 35, 45, and 55 °C, respectively. EIS validated the PDP tests, showing that sodium succinate displaces the water molecules at the interface, creating an adsorption film by complexing with ferrous ions. The film thickness was calculated, and sodium succinate was able to produce a thicker protective film (span of nanometers) relative to the reference at every temperature. The adsorption of sodium succinate follows the Temkin adsorption isotherm. ΔG0ads was found to be -32.75 kJ/mol, indicating that the inhibitor adsorption is a combined physisorption and chemisorption process. Different surface characterizations were utilized to substantiate the adsorption of sodium succinate, these include scanning electron microscopy, energy-dispersive X-ray spectroscopy, and micro-Raman spectroscopy. Finally, quantum chemical calculations showed that the delocalized electrons in the carboxyl group have high HOMO energies and electrostatic potential, which facilitates the adsorption of sodium succinate corrosion inhibitor onto the carbon steel rebar surface.

Sequential Use of Orthogonal Self‐Assembled Monolayers for Area‐Selective Atomic Layer Deposition of Dielectric on Metal

AbstractAlthough there have been several demonstrations of area‐selective atomic layer deposition (AS‐ALD) of dielectric on dielectric in metal/dielectric patterns, the reverse process of selective dielectric on metal (DoM) is not as well developed due to the challenge of inhibiting only the dielectrics. Unavoidable native oxide formation on metals tends to lead to similar surface chemical properties between metal and dielectric substrates, decreasing the selectivity in inhibitor adsorption. Hence, to achieve DoM, preventing unwanted inhibitor adsorption on metals is critical. This study demonstrates a two‐step strategy of first applying a dodecanethiol (DDT) self‐assembled monolayer (SAM) on a Cu/SiO2 pattern to protect the Cu surfaces from subsequent deposition of an octadecyltrimethoxysilane (OTMS) inhibitor, which then selectively forms an OTMS SAM on SiO2. It is further shown that by removing the DDT protector with thermal treatment before AS‐ALD, subsequent ALD growth on Cu is not affected while ALD remains blocked on the OTMS‐covered SiO2 regions. Using this strategy, DoM is demonstrated with selectivity above 0.9 after 5.6 nm of ZnO and 1.5 nm of Al2O3 ALD. This work presents a new approach to expand the material systems available to AS‐ALD which may help enable more applications in microelectronics, optoelectronics, and energy.

The use of ellipsometry for studying adsorption of organic corrosion inhibitors from aqueous solutions on metals. Review. Part 1. Methods for obtaining adsorption isotherms

The use of ellipsometry for studying adsorption of organic corrosion inhibitors from aqueous solutions on metals. Review. Part 1. Methods for obtaining adsorption isotherms

Synthesis of gemini cationic surfactants-based pyridine Schiff base for steel corrosion and sulfate reducing bacteria mitigation

Three gemini cationic surfactant with different hydrophobic tails labeled GSBO, GSBD, and GSBH based azomethine and pyridine nuclei have been synthesized and confirmed spectroscopy via FTIR, 1HNMR, and mass spectroscopy. The surface and thermodynamic study were conducted via measurement the surface tension measurements at different temperatures for well examining their corrosion inhibition efficiency. The affinity of the GSBO, GSBD, and GSBH toward micelle formation and adsorption at interface were hydrophobic and temperature dependent. The C-steel corrosion suppression via the synthesized GSBO, GSBD, and GSBH in 1 M H2SO4 were evaluated using electrochemical impedance spectroscopy, weight loss and polarization techniques, demonstrating their efficient affinity to mitigate the steel corrosion. Increasing the surfactant hydrophobicity exhibit higher ability to suppress the corrosion, as confined by the higher inhibition efficiency achieved by GSBH of 94.5 % that matched with higher adsorption affinity as claimed from the surface and thermodynamic investigation. The Tafel examination clarified GSBO, GSBD, and GSBH behaves as mixed type inhibitors following modified Langmuir isotherm. The inhibitors adsorption on C-steel was confirmed by XPS and SEM surface examination. Ultimately the synthesized azomethine based pyridine nuclei showed affinity to mitigate the sulfate reducing bacteria (SRB) with cut-off point observed for GSBO.

Inhibition of the erosion-corrosion of elbow by synergistic action of swirling flow and inhibitor

The experiments of using inhibitors to inhibit the erosion-corrosion of elbows under the conditions of liquid-solid non-swirling flow and swirling flow were designed to evaluate the inhibition of erosion-corrosion of elbows under the combined action of swirling flow and inhibitors. The experiments were carried out by a circulating loop system in combination with a variety of test methods and computational fluid dynamics (CFD) simulation. It is demonstrated that the addition of inhibitors under non-swirling flow and swirling flow conditions can inhibit effectively the erosion-corrosion rate and its four components (pure corrosion, pure erosion, corrosion-enhanced erosion, and erosion-enhanced corrosion). The comprehensive inhibition efficiencies of the synergistic action of swirling flow and inhibitor on the four components of erosion-corrosion are higher than the inhibition efficiencies of inhibitor acting on the four components alone. The hydrodynamic characteristics of swirling flow produce the sand suspension effect and mass transfer enhancement effect which facilitate the adsorption of inhibitor on the working electrode surface and acting in conjunction with the oxide film to form a lamellar protective corrosion product layer with stronger integrity and compactness.

Novel Nanocomposite Coated Proppants for Enhanced Scale Inhibition Lifetime in Tight Shale Formations

Controlling scale deposition in tight formations such as shale is commonly achieved by combining fracturing stimulation with squeeze treatment. The squeeze treatment process’s success relies on the targeted formation’s ability to adsorb the right amount of scale inhibitor and slowly release it during hydrocarbon production. The inhibition lifetime of a standard squeeze treatment lasts from 3 to 6 months depending on the compatibility between the formation and scale inhibitor–operators desire a prolonged inhibition lifetime. Herein, a novel approach of resin-based nanocomposite coated proppants is developed to act as a propping agent and high active surface platform for scale inhibitors to be adsorbed and subsequently slowly released during oil production. In this study, proppants were coated with a thin layer of polyurethane, followed by a layer of carbon-based nanomaterials (Multi-Wall Carbon Nanotubes (MWCNTs) and Graphene Nanoplatelets (GNPs)), and characterized using Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive X-ray Analysis (EDX). Due to the concerns of climate change, polyurethane was selected due to its quick curing at lower temperatures and minimal environmental impacts. The potential of the proposed proppant to enhance the adsorption and slow the desorption of a Diethylenetriamine Penta (DTPMP) scale inhibitor, the necessary strength to withstand closure stress, and its thermal stability were evaluated. FESEM and EDX results revealed that an ultrathin uniformed coating layer was established. The stress resistance data showed that the proposed proppants (MWCNTs-RCP and GNPs-RCP) could withstand closure stress as high as 68.9 MPa with less than 10 wt % fines production. In addition, the thermal stability of MWCNTs-RCP and GNPs-RCP reached 347 °C. Scale inhibitor adsorption experiments showed that MWCNTs-RCP and GNPs-RCP adsorbed 583.5 mg/kg and 832.0 mg/kg of DTPMP, respectively. Desorption results indicated that MWCNTs-RCP and GNPs-RCP extended the inhibition lifetime of DTPMP by 400% PV compared to a conventional proppant. Intraparticle diffusion was found to dominate the desorption of DTPMP from MWCNTs-RCP and GNPs-RCP, which explains the slow desorption rate they exhibited. Therefore, the developed proppants could be a promising multifunctional proppant in the oil and gas industry.

The quaternary ammonium salts as corrosion inhibitors for X65 carbon steel under sour environment in NACE 1D182 solution: Experimental and computational studies

The effect of quaternary ammonium salts (DDPC and DDQC) with different concentrations on the corrosion inhibition of X65 carbon steel in the sour brine solution at different temperatures were investigated by weight loss, electrochemical measurements, surface analysis (SKP, AFM, SEM, EDS, and ATR-FTIR), and theoretical calculations (DFT, Monte Carlo, and molecular dynamics). It was found that the corrosion rate decreased with increasing inhibitor concentration, and the inhibition efficiency was about 98%. The adsorption of inhibitors on the metal surface followed the Langmuir adsorption isotherm. Furthermore, inhibitors showed good performance at elevated temperatures. The computational studies supported the experimental data well.

Evaluating the Corrosion Inhibition Efficiency of Pyridinium-Based Cationic Surfactants for EN3B Mild Steel in Acidic-Chloride Media

Two new effective corrosion inhibitors, namely N-(n-octyl)-3-methylpyridinium bromide (Py8) and N-(n-dodecyl)-3-methylpyridinium bromide (Py12), have been presented. The cationic pyridinium-based surfactants were analyzed for the corrosion protection of general purpose steel (EN3B) against a strong corrosive media (3.5% NaCl, pH 1.5). The results of the electrochemical measurements, i.e., Tafel polarization, linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) revealed a mixed-type behavior of both inhibitors, and the maximum inhibition efficiency (IE) achieved with Py8 and Py12 was 85% and 82%, respectively. The process of adsorption of synthesized inhibitors followed the Langmuir adsorption isotherm, and a higher value of Kads highlighted the existence of strong interaction between inhibitors and the EN3B mild steel surface. Furthermore, the values of ΔG°ads were calculated to be −32 kJ mol−1 for Py8 and −33 kJ mol−1 for Py12, indicating the coexistence of both physisorbed and chemisorbed molecules. The surface morphology of EN3B mild steel samples was observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM), where the reduced surface roughness in the presence of Py8 and Py12 in chloride media further supported the evidence of an efficient inhibition process. Density functional theory (DFT) calculations reveal excellent correlation with the experimental results, with Py8 showing superior corrosion inhibition potential, signifying that the alkyl chain length and intramolecular charge transfer are crucial factors in deciding the inhibition performance of the synthesized cationic surfactants. Furthermore, this study proposes the mechanism for the adsorption of the surfactant-based inhibitors over the EN3B mild steel surface, which leads to the formation of an effective and protective anticorrosive film.

Suppression of steel corrosion via some gemini cationic surfactant-based Schiff base: experimental and theoretical investigations

Abstract Steel is involved extensively in engineering vast constructing units in many industries and can undergo to corrosion by some chemical and/or electrochemical reactions with the environment. Therefore, designating an organic inhibitor with a specific chemical structure will participate in steel protection via enhancing their adsorption on the steel surface. Three gemini cationic surfactants based on azomethine with different hydrophobic tails labeled GSBI8, GSBI12, and GSBI16 have been designated and evaluated as corrosion inhibitors utilizing electrochemical impedance spectroscopy (EIS), gravimetrical and potentiodynamic polarization techniques. Importantly, the surfactant tail regulated the corrosion inhibition performance; with increasing the surfactant tail length, their inhibition efficiency enhanced because of their higher adsorption affinity. The inhibition efficiency of GSBI8, GSBI12, and GSBI16 reached 95.52, 96.72, and 97.1% respectively (EIS measurements). The Tafel examination clarified that GSBI8, GSBI12, and GSBI16 inhibitors behave as mixed type inhibitors following the modified Langmuir isotherm. The inhibitors adsorption on C-steel was confirmed by SEM surface examination. Finally, the DFT and MCs point of views investigation supported the experimental performance of the tested GSBI8, GSBI12, and GSBI16 inhibitors and specially their dependence on surfactant tail length.

Quantification of soil heterotrophic nitrification in 15N tracing and specific inhibitor approaches

AbstractTwo methodological approaches are commonly used to investigate heterotrophic nitrification (Nith) in soil: process inhibitions and 15N tracing. Although many studies have reported Nith based on 15N tracing approaches, estimates via specific inhibitor are less common. Therefore, we conducted a meta‐analysis to illustrate the similarities and differences of the results of soil Nith between the two approaches. We observed that the average result of gross Nith rate was significantly lower with the 15N tracing approach (1.32 mg N kg−1 day−1) than with the inhibitor approach (3.54 mg N kg−1 day−1) (p < 0.01). Possible explanations include incomplete inhibition of autotrophic nitrification (Nita) due to the adsorption of inhibitors on soil aggregates and the fact that the estimation of Nith via 15N tracing quantifies only the Nith fraction related to organic N oxidation. The results of linear‐mixed models indicated that soil C:N ratio had a significantly positive effect on the difference of Nith estimated via 15N tracing and inhibitor approach, which was also supported by the paired data between natural and C‐ and N‐ manipulated soil. The average contribution of Nith to total nitrification, estimated by the ratio of Nith:(Nith + Nita) or the capacity of NO2−/NO3− production when Nita was inhibited, in the two approaches were not significantly different (34% vs. 33%). While, soil C:N ratio also caused a significantly positive effect on the contribution of Nith to soil total nitrification (p < 0.05). In conclusion, the result of the relative contribution of Nith is less affected by approach than the result of gross Nith rate. In addition, soil C and N substrate availability is likely to be a critical factor affecting the estimation of soil Nith by the two approaches.Highlights Process inhibitors and 15N tracing are two commonly used methods to quantify soil heterotrophic nitrification (Nith). A meta‐analysis was carried out to compare the results of soil Nith between the two methods. There was a significant difference of the rate of Nith estimated via the two methods, while the contribution of Nith to total nitrification was similar. Soil C and N substrate appeared to influence the estimation of soil Nith via the two approaches.

Inhibition mechanism of interaction effect between charged character of inhibitor and rare earth elements for Mg-Gd-Y alloy

The inhibition mechanism of four inhibitors with different charge on Mg-Gd-Y alloy was investigated experimentally and theoretically. The different charge of inhibitor evoked the preferential adsorption behavior, changing the susceptibility of Mg-Gd-Y alloy to micro-galvanic corrosion. Moreover, the adsorption of inhibitor changed the surface energy of embryos of corrosion product, and strongly suppressed the nucleation rate of corrosion product, leading to poor protective performance. Thus, the inhibitor with anion, exhibiting satisfactory inhibition efficiency for AZ/AM series alloys, showed worse inhibition for the Mg-Gd-Y alloy. Finally, the strategy to select and/or synthesize inhibitors for Mg-RE alloys was presented.

Adsorption and Surface Analysis of Sodium Phosphate Corrosion Inhibitor on Carbon Steel in Simulated Concrete Pore Solution.

Corrosion of steel-reinforced concrete exposed to marine environments could lead to structural catastrophic failure in service. Hence, the construction industry is seeking novel corrosion preventive methods that are effective, cheap, and non-toxic. In this regard, the inhibitive properties of sodium phosphate (Na3PO4) corrosion inhibitor have been investigated for carbon steel reinforcements in 0.6 M Cl- contaminated simulated concrete pore solution (SCPS). Different electrochemical testing has been utilized including potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and Mott-Schottky plots to test Na3PO4 at different concentrations: 0.05, 0.1, 0.3, and 0.6 M. It was found that Na3PO4 adsorbs on the surface through a combined physicochemical adsorption process, thus creating insoluble protective ferric phosphate film (FePO4) and achieving an inhibition efficiency (IE) up to 91.7%. The formation of FePO4 was elucidated by means of Fourier-transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). Quantum chemical parameters using density functional theory (DFT) were obtained to further understand the chemical interactions at the interface. It was found that PO43- ions have a low energy gap (ΔEgap), hence facilitating their adsorption. Additionally, Mulliken population analysis showed that the oxygen atoms present in PO43- are strong nucleophiles, thus acting as adsorption sites.

(Digital Presentation) Investigation of Microstructure Dependent Inhibitor Adsorption Mechanism on Carbon Steel By in Situ Atomic Force Microscopy

In the petroleum industry, organic surfactant type inhibitors have been widely applied in the oil and gas industry considering their high efficiency. Carbon steels with various carbide contents have also been used extensively as pipeline materials during the transport and storage of crude oil due to their excellent mechanical properties and low cost. The previous investigation of inhibition mechanism on carbon steel is limited by lack of surface characterization techniques at a molecular level. Atomic force microscopy (AFM) can not only provide localized visual observation, but can also achieve the detection of mechanical properties of an inhibitor film. In this study, in situ AFM contact mode friction imaging and in situ AFM tapping mode phase imaging techniques have been applied to investigate the influence of the ferritic-pearlitic microstructure of carbon steel on inhibitor adsorption mechanisms during CO2 corrosion under different inhibitor concentrations. At concentration above surface saturation, AFM contact mode friction images show a large friction contrast between inhibitor covered cementite structures and ferrite structures, while in the absence of inhibitor, this friction contrast almost disappears, indicating the inhibitor adsorption induced this difference. AFM tapping mode phase images indicate uniform adsorption of inhibitor on both cementite and ferrite structures.The differences observed in these AFM analyses indicate that the adhesion force of inhibitor molecules on cementite could be smaller than on ferrite, or the molecular orientations of inhibitor molecules adsorbed on cementite and ferrite structures could be different. The special adsorption behavior of inhibitor molecules on cementite means the carbide component of the microstructure could directly influence inhibitor adsorption and may decrease inhibitor efficiency. Simultaneous linear polarization resistance tests in electrochemical AFM (EC-AFM) cell indicates a maximum inhibition efficiency at concentration above saturation.Keywords : Contact mode AFM, friction contrast, tapping mode AFM, phase contrast, cementite, ferrite, organic inhibitor, adhesion force.Statement of importance:Studies related to inhibitor adsorption mechanisms on ferritc-pearlitic carbon steels can be connected with the practical issues that iron carbide can impair the corrosion inhibitor performance on carbon steels. This AFM work connects the corrosion inhibition effect with the carbon steel components at a molecular level for the first time. Physical explanations regarding the interactions between inhibitor molecules and carbon steel microstructures can also be provided with the assistance of molecular simulations.Figure caption: Contact and tapping mode AFM images of inhibitor film formed on UNS G1018 steel at 2 CMC (100ppm) tetradecyldimethylbenzylammonium inhibitor + 1 wt% NaCl. The contact mode friction image indicates a large friction contrast between inhibitor covered cementite and ferrite structure, while the tapping mode phase image indicates a negligible softness contrast between cementite and ferrite structure. Figure 1

(Corrosion Division Rusty Award for Mid-Career Excellence) Rust At a Glance: Electrochemical Thermodynamics and Kinetics of Porous Corroding Interfaces

The development of a rust layer is governed by physico-chemical processes at the electrode/electrolyte porous interface, including electrochemical thermodynamics and kinetics, as well as transport and reaction processes. While rust can be protective under passive and inert regions found on the Pourbaix diagram, it becomes interesting to see whether its stability is compromised under harsh conditions that lead to active dissolution of this porous interface.Thermodynamics calculations can predict phase transformation, which nucleation and growth is governed by the chemical activity of the porous interfaces as well as by the saturation of the electrolyte solution. Understanding the electrochemical interface is a major challenge to unravel the corrosion mechanism of porous systems. The heterogeneous nature of the oxide structure as well as the development of amorphous gel regions influences the formation of active sites and point defects with a high lability for reacting with gas phases dissolved, entrapped, or occluded within interfacial substructures.The stabilization and corrosion protection of the rust interface requires to understand the adsorption of corrosion inhibitors on the surface of the active site on the electrode ‒ creating a stable protective passive film. Enthalpy and entropy of the dissolution process can explain the spontaneous formation of a rust layer as well as the displacement of water molecules, which ultimately will result in the effective physico-chemical adsorption of the inhibitor molecules.In summary, this communication is aimed to present the role of rust at a glance, and its implications on the electrochemical corrosion mechanisms on porous interfaces. The application of electrochemical fundamentals and first principles combined with state of the art electrochemical, chemical and surface characterization techniques provides a comprehensive vision and mission on current trends in corrosion and protection of steel in porous media.