General corrosion of carbon steel in a synthetic concrete pore solution

In this study, we reviewed our recent work on the general corrosion of carbon steel (P355QL2) overpack material for the isolation of high-level nuclear waste in Belgium's supercontainer concept. By using electrochemical impedance spectroscopy and by optimizing the mixed potential model, which incorporates quantum mechanical tunneling of charge carriers across the barrier layer to describe the kinetics of the partial cathodic process, we evaluated all parameters in the model as a function of independent variables such as voltage, temperature, and pH. By delineating the partial anodic and cathodic processes, we found that the corrosion rate (CR) is independent of voltage over the voltage range from 0.2 to −1.0 V_SHE, which is predicted to be experienced in the repository. Furthermore, the CR is found to increase strongly with decreasing pH and increasing temperature.     

Aminopyrimidine derivatives as inhibitors for corrosion of 1018 carbon steel in nitric acid solution

The effect of some aminopyrimidine derivatives on the corrosion of 1018 carbon steel in 0.05 M HNO₃ solution was studied using weight loss and polarization techniques. The percentage inhibition efficiency was found to increase with increasing concentration of inhibitor and with decreasing temperature. The addition of KI to aminopyrimidine derivatives enhanced the inhibition efficiency due to synergistic effect. The inhibitors are adsorbed on the steel surface according to Temkin isotherm. Some thermodynamic functions were computed and discussed. It was found that the aminopyrimidine derivatives provide a good protection to steel against pitting corrosion in chloride containing solutions.     

The corrosion behavior of carbon steel in CO2‐saturated NaCl crevice solution containing acetic acid

The corrosion behavior of X52 carbon steel electrodes in CO₂‐saturated NaCl crevice solution containing HAc was investigated by electrochemical measurements. Chemical environment measurements by Cl^? and pH microprobes show an enrichment of Cl^? ions and an increase of pH values inside the crevice. Moreover, both increments could accelerate with the decreasing dimension of the crevice mouth due to the high diffusive resistance. When the electrode in the crevice solution is coupled with the electrode in bulk solution, the alkalization and the enrichment of Cl^? ions in the crevice solution can result in a negative shift of potential of the electrode in crevice solution, while the potential of the electrode in bulk solution shifts positively during the corrosion process. Thus, a galvanic corrosion is established with the electrode in the crevice solution acting as anode while another in the bulk solution as cathode, i.e., the corrosion in the crevice solution was enhanced while the corrosion in the bulk solution was retarded. The anodic dissolution and the cathodic reduction processes dominate in the crevice solution and in the bulk solution, respectively.     

An amino-based protic ionic liquid as a corrosion inhibitor of mild steel in aqueous chloride solutions

Protic ionic liquids (PILs) have shown to be promising substances as corrosion inhibitors (CIs). In line with this, the aim of this study is to study the performance and propose the corrosion inhibition mechanism of N-methyl-2-hydroxyethylamine (M-2HEAOL) and bis-2-hidroxyethylamine (B-HEAOL) oleate, for mild steel, in a neutral chloride solution. Electrochemical characterization was conducted under static and hydrodynamic conditions, and it was revealed that M-2HEAOL and B-HEAOL worked as mixed-type CIs with more interference on the anodic reaction. Inhibition efficiency depended on the concentration reaching 97% of inhibition efficiency in 5 mmol/L concentration. Scanning electron microscopy, optical interferometry, Raman spectroscopy, and Fourier-transform infrared spectroscopy are used to elicit the chemical composition of the surface film and corrosion morphology of steel in the presence of CIs, the adsorption processes of which involved physical and chemical adsorption between metal and different parts of ionic liquids. The results allowed the proposition of a corrosion inhibition mechanism.     

Evaluation of Eulychnia acida and Echinopsis chiloensis (Cactaceae) extracts in inhibiting corrosion of carbon steel in HCl solution

In the present study, the activity of extracts obtained from the stems of two endemic species of the central–northern region of Chile (Eulychnia acida [Copao] and Echinopsis chiloensis [Quisco]), was evaluated as potential corrosion inhibitors for carbon steel in 0.1 M HCl. The total content of phenols and flavonoids in the extracts was determined, and the main components were identified by high-performance liquid chromatography–mass spectrometry, being similar in both species. The inhibition efficiency of extracts was evaluated by mass loss measures, Tafel polarization curves, and electrochemical impedance spectroscopy. The assay results showed similar values in inhibition percentages, around 88% at extract concentrations of 1,500 ppm. The adsorption on the steel surface followed the Langmuir model adsorption isotherm, whose thermodynamic parameters (ΔG°_ads for Copao and Quisco, −17.81 and −17.70 kJ/mol, respectively) suggest a physisorption mechanism. The scanning electron microscopy analyses showed that in the presence of the extracts, the surface of the steel is covered by a thin film that allows the sanding marks to be visualized; while without the extracts the surface is rough due to the HCl corrosion effect.     

Study of thioureas derivatives synthesized from a green route as corrosion inhibitors for mild steel in HCl solution

The behaviour of 1,3-dibenzylthiourea (DBTU) and 1-benzyl-3-diisopropylthiourea (DPTU) have been investigated as carbon steel corrosion inhibitors in HCl solution by weight loss measurements, potentiodynamic polarization curves, electrochemical impedance and scanning electron microscopy analysis. Quantum chemical calculation was applied to correlate electronic structure parameters of thiourea derivatives with their inhibition performances. DPTU results were slightly superior to those obtained in the presence of DBTU, showing that the replacement of one benzyl group for two isopropyl groups enhances the inhibitory properties. The 1,3-dibenzylurea derivative has also been studied in order to assess the importance of the sulphur atom to the inhibitory effect.     

Investigation of a hydrophobically associating AMAHS polyacrylamides: A new corrosion inhibitor for mild steel in HCl

A polyacrylamide with capsaicin-derived monomers (AM–MAA–AMPS–HMBA–SMA; AMAHS) was synthesized and investigated as a novel environment-friendly polymer inhibitor for Q235 mild steel at 25°C in 1 M HCl solution. The inhibition efficiency was evaluated by weight loss measurements, electrochemical experiments, and surface investigation methods as well as by theoretical calculations. Experimental results indicated that the efficiency of AMAHS was up to 94.86% at the concentration of 2 g/L. Electrochemical tests and surface morphology analysis showed that AMAHS served as a mixed-type corrosion inhibitor, which could be adsorbed and self-assembled on the surface of mild steel forming a highly hydrophobic protective film (contact angle of 172°). Density functional theory calculations revealed that heteroatoms in AMAHS, such as O, N, S, are active sites in forming coordination bonds with surface iron atoms. In addition, hydrophobic groups played an important role in protecting the metal surfaces from corrosion media.     

Experimental and theoretical studies of thiazoles as corrosion inhibitors for mild steel in sulphuric acid solution

The inhibition effects of 2-amino-5-mercapto-1,3,4-thiadiazole (2A5MT) and 2-mercaptothiazoline (2MT) on mild steel corrosion in 1.0 M H₂SO₄ were studied with potentiodynamic polarization, linear polarization resistance and electrochemical impedance spectroscopy techniques. It was shown that both 2A5MT and 2MT act as good corrosion inhibitors for mild steel protection. The high inhibition efficiencies were attributed to the simple blocking effect by adsorption of inhibitor molecules on the steel surface. The effects of the presence of extra NH₂ group and N atom in 2A5MT on the ability to act as corrosion inhibitors were investigated by theoretical calculations.     

An EIS study of the effect of the pedant group in imidazolines as corrosion inhibitors for carbon steel in CO2 environments

Electrochemical impedance spectroscopy (EIS) measurements were carried out to study the corrosion inhibition of carbon steel in 3 % NaCl with and without diesel saturated with CO₂ at 50 °C. The inhibitors examined were hydroxyethyl (HEI‐18), amino ethyl (AEI‐18), and amide ethyl imidazolines (AMEI‐18). When the oily phase, i.e diesel, is absent, the inhibition efficiency of the imidazolines is low, around 80 %. It was found, however, that the inhibition dramatically increased with the presence of the oily phase, because the imidazolines are able to act as both emulsifiers and corrosion inhibitors. Experimental results showed an increase in the film resistance (R_f), charge transfer resistance (R_ct), capacitance of the film and the capacitance of the double layer values with the addition of inhibitor in presence of the oily phase also in several orders of magnitude. The most effective inhibitor in presence of diesel is a solution of AMEI‐18, as the oily phase is carried to the surface also. This is due to the presence of two large alkyl groups than the only chain present in the HEI‐18 and AEI‐18 imidazolines with better hydrophobic properties associated with the formation of a protective film that reduces drastically the corrosion process. The effects of the interaction of inhibitors with hydrocarbons and the correlation on the performance of inhibitor films have been examined.     

Design and synthesis of a novel class of inhibitors for mild steel corrosion in acidic and carbon dioxide-saturated saline media

p-(9-(2-Methylisoxazolidin-5-yl)nonyloxy)benzaldehyde I, prepared using a cycloaddition protocol, was elaborated into its cinnamaldehyde derivative II which upon quarternization with propargyl chloride afforded III bearing an interesting blend of structural traits suitable for imparting inhibition of mild steel corrosion. Novel compounds I–III showed efficient inhibition against mild steel corrosion in CO₂–0.5 M NaCl (40 °C, 1 atm; 120 °C, 10 bar), 1, 4, 7.7 M HCl, and 0.5 M H₂SO₄ at 60 °C as determined by gravimetry and electrochemical methods. The presence of carbonaceous surface and nitrogen, as revealed by XPS study, indicated the formation of a film covering the metal surface, which imparted corrosion inhibition.     

Effectiveness of some diquaternary ammonium surfactants as corrosion inhibitors for carbon steel in 0.5 M HCl solution

Four Gemini surfactants were synthesized and characterized using elemental analysis, FTIR and ¹H NMR spectroscopy. The synthesized compounds were evaluated as corrosion inhibitors for carbon steel in 0.5 M HCl solution. The inhibition efficiencies of the tested inhibitors were depended on the hydrophobic chain length and the used doses of the inhibitors. The polarization measurements showed that these inhibitors are acting as mixed inhibitors for both anodic and cathodic reactions. The results showed that the inhibition efficiencies were increased by increasing the inhibitor doses and the hydrophobic chain length and reached the maximum at 500 ppm by weight for stearyl derivative. The efficiencies obtained from the impedance measurements were in good agreement with those obtained from the gravimetrical and polarization techniques which prove the validity of these tolls in the measurements of the tested inhibitors.     

Study of corrosion behaviour of A106 carbon steel absorber for CO2 removal in amine promoted hot potassium carbonate solution (Benfield solution)

The CO₂ absorber is one of the largest pressure vessels in ammonia plants, which are suffering from severe corrosion problems worldwide. The aim of the present study is to examine the corrosion behaviour of A106 carbon steel absorber for CO₂ removal in amine promoted hot potassium carbonate solution (Benfield solution). This study simulates CO₂ removal unit in ammonia production process at Abu Qir Fertilizers and Chemical Industries Company (Alexandria, Egypt) and many other plants all over the world. A typical Benfield solution contains hot potassium carbonate K₂CO₃, potassium bicarbonate KHCO₃, diethanol amine (DEA) as a promoter and potassium metavanadate KVO₃ as corrosion inhibitor. The rate of galvanic corrosion of carbon steel absorber/stainless steel pall packings couple in Benfield solution was measured without adding the corrosion inhibitor KVO₃ in order to measure the influence of corrosive solution. The corrosion rate was measured by weight loss technique in relation to different operating parameters such as solution velocity, solution temperature, %K₂CO₃, CO₂ loading, %DEA and the effect of the presence of solution contaminants. In general, increasing solution velocity, solution temperature, %K₂CO₃, CO₂ loading and the presence of solution contaminations increase the corrosion rate. However, the increase in %DEA in solution decreases the corrosion rate. The strong dependence of corrosion rate on both solution and gas velocities indicates the diffusion controlled nature of the corrosion process. In addition, estimation of activation energy revealed a value of 4·8 kcal mol^?1. Surface morphology study depicted the presence of a porous solid film of corrosion products on carbon steel surface. It has been found that the liquid phase diffusion of bicarbonate to the steel solution interface is the rate determining step.     

An in situ FT‐IR evaluation of candidate organic corrosion inhibitors for carbon steel in contact with alkaline aqueous solutions

The influence of some organic additives on the anodic behaviour of a carbon steel electrode in contact with alkaline aqueous solutions was studied by in situ Fourier transform infrared (FT‐IR) spectroscopy. FT‐IR spectroscopy allows to obtain information at the molecular level regarding the metal‐electrolyte interface. The following molecules have been considered: (i) benzyldimethylphenylammonium chloride (BDMPAC), (ii) glutamic acid, (iii) triethylenetetramine (TETA), (iv) sodium tartrate and (v) sodium benzoate. Potential‐dependent spectra have been recorded for the different investigated systems. Quantitative information about the formation kinetics of corrosion products was derived by numerical analysis of the peak area as a function of the applied potential for the different systems investigated.     

Electrochemical and quantum chemical studies of 3,4-dihydropyrimidin-2(1H)-ones as corrosion inhibitors for mild steel in hydrochloric acid solution

The inhibition effect of 3,4-dihydropyrimidin-2(1H)-ones (DHPMs) on the corrosion of mild steel in hydrochloric acid medium has been investigated using weight loss measurements, electrochemical impedance spectroscopy, potentiodynamic polarization and quantum chemical study. Among the compounds studied, DHPM-3 exhibited the best inhibition efficiency η (%) 99% at 10 mg L⁻¹ at 308 K. Polarization measurements indicate that all the examined compounds are of mixed-type inhibitor. The adsorption of studied compounds obeyed the Langmuir’s adsorption isotherm. The electronic properties obtained using quantum chemical approach, were correlated with the experimental inhibition efficiencies.