Mechanism of steel corrosion in concentrated NaOH solutions

A study has been made of the mechanism of corrosion of carbon steel in 1–19 N NaOH at 25–80°C. The polarization curves were obtained with a rotating steel disk electrode, and the rotating ring-hemisphere electrode technique was used to identify soluble corrosion products. It was found that at the active anodic dissolution potentials, steel dissolves to form HFeO⁻₂ ions. Both the anodic and cathodic polarization curves exhibited a well defined Tafel regime, and the electrokinetic parameters were obtained for the corrosion of steel. The results were interpreted with a corrosion mechanism based on the decomposition of molecular water to hydrogen at the cathodic sites, and the active dissolution of iron to HFeO⁻₂ ions via two adsorbed intermediates, FeOH_ads and Fe(OH)_2,ads, at the anodic sites. The theoretically derived anodic Tafel slope, anodic reaction order, corrosion potential, and corrosion current density agreed quantitatively with the experimental values. At the potentials above the anodic Tafel regime and in the neighborhood of the active—passive transition potential, steel dissolved to form both the bi-valent and tri-valent iron species, HFeO⁻₂ and FeO⁻₂ ions. The thermodynamic considerations revealed that FeO⁻₂ ion was formed from the oxidation of Fe(OH)_2,ads intermediate, rather than from the oxidation of HFeO⁻₂ ion on steel surface.     

Evaluation of Some Nonionic Surfactants Derived From Vanillin as Corrosion Inhibitors for Carbon Steel During Drilling Processes

Four eco‐friendly nonionic surfactants based on vanillin were investigated as corrosion inhibitors against carbon steel dissolution during the drilling process in the oil field. The corrosion inhibition efficiencies of the tested compounds were determined using weight loss, electrochemical polarization, and electrochemical impedance techniques. The data obtained show that the nonionic surfactants prevent the corrosion of drilling tools and their inhibition efficiency increased with an increase in their concentration. Tafel curves revealed that the surfactants under study act as mixed inhibitors. The adsorption of the inhibitors on carbon steel surface decreases the double‐layer capacitance. The inhibition efficiencies of the surfactants were influenced by their chemical structure and surface activity.     

CO2 corrosion of carbon steel in the presence of acetic acid at higher temperatures

The corrosion behaviour of X 65 carbon steel in the presence of acetic acid in N₂- and CO₂-saturated systems has been investigated using electrochemical techniques. The presence of acetic acid does not influence the anodic reaction but strongly accelerates the cathodic reaction. The cathodic reaction and consequently the corrosion rate of mild steel in the CO₂-saturated system increase with increase in acetic acid concentration and temperature. From the values of the apparent activation energies, the corrosion reaction in the absence of acetic acid was found to be under mixed interfacial reaction/diffusion control while interfacial reaction control dominates in the presence of acetic acid. The reduction of adsorbed undissociated acetic acid on the metal surface is proposed as the key species primarily responsible for accelerated corrosion rate at all temperatures.     

Mechanistic aspects of electrochemical corrosion of aluminum alloy in ethylene glycol–water solution

The electrochemical corrosion behavior of 3003 aluminum (Al) alloy in ethylene glycol–water solutions was studied by electrochemical measurements and surface analysis techniques through an impingement jet system. Al corrosion in aerated, stationary solution is a mixed-controlled process, i.e., both activation and mass-transfer steps control the corrosion reaction. Upon flowing of solution, no matter if sand particles are contained, Al corrosion is an activation-controlled process. In addition to Al oxide film, a layer of Al-alcohol film will also be formed on the electrode surface in ethylene glycol–water solution, contributing to inhibition of anodic dissolution of Al. In the absence of oxygen, a stable passivity could also be achieved on Al alloy. The main cathodic reaction is either reduction of water or reduction of ethylene glycol. However, the reduction of water and ethylene glycol would not be as significant as that of oxygen. As a consequence, the resultant film is not as stable as that formed in the presence of oxygen, as shown in polarization measurements. Al corrosion reaction in mixed-controlled by activation step and mass-transfer step through the anodic surface film. The coverage of the adsorbed intermediate product on Al electrode surface is expected to be very small under the impingement of fluid and sand particles, which results in the generation of an inductive loop in Nyquist diagrams measured on Al electrode in ethylene glycol–water solution.     

pH、离子浓度、温度对20A碳钢在氯化钠溶液中电化学腐蚀行为的影响

报道通过电化学工作站、扫描电子显微镜、XRD衍射仪及原子分光光度仪研究pH、离子浓度、温度对20A碳钢腐蚀行为的影响。根据实验结果分析认为：室温（10℃C）,pH=8下,OH^-与Cl^-在材料表面发生竞争吸附,低浓度氯离子溶液中OH^-对材料的腐蚀起到了较好的抑制作用;在高浓度氯离子溶液中,Cl^-对OH^-的竞争取得优势,Cl^-的侵蚀作用破坏了OH对电极表面的保护,使得碳钢的腐蚀加剧;随着温度的升高,加速了溶液离子的扩散,使得OH^-对电极的保护遭受破坏,氯离子的迁入能力增强,导致碳钢的Rct递减,Icorr增大;在70℃、0．1mol／LCl^-溶液中挂片6h,试片表面可以看到明显的两层结构,外层为疏松的Fe3O4腐蚀产物,内层可能是Fe（OH）3。     

Corrosion inhibition of carbon steel by N,N′-Dimethylaminoethanol in simulated concrete pore solution contaminated with NaCl

The inhibition behavior of N,N′-Dimethylaminoethanol (DMEA) as an organic corrosion inhibitor for carbon steel in simulated concrete pore solution contaminated with chloride ions encountered in the Mediterranean seawater (0.5 mol L^?1), at different temperatures, was investigated by means of weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The results obtained confirm that DMEA is an efficient corrosion inhibitor over the whole range of temperatures studied; it can significantly reduce the corrosion rate of carbon steel. The inhibition efficiency (IE%) increases as the DMEA concentration rises; it reaches its maximum average value of 80% at about 0.125 mol L^?1. The corrosion inhibition of carbon steel by DMEA occurs through chemisorption of inhibitor molecules on the active sites, according to the Langmuir isotherm; this leads to the formation of a passive layer on the metal surface which separates the metal from direct contact with the corrosive medium and hence keeps the interface in a passive state. Furthermore, the activation parameters of corrosion processes were determined and discussed.     

Electrochemical reduction of carbon dioxide and the effect of the enzyme carbonic anhydrase 11 on iron corrosion

The corrosion of pure iron in carbon dioxide saturated solutions at low temperatures has been investigated in this study. Both dc polarisation and ac impedance techniques were used in conjunction with a rotating disc electrode to investigate the reaction sequence leading to hydrogen evolution at 30°C. The results indicate that protons from the low pH solution, the bicarbonate ion and the undissociated carbonic acid molecule contribute to the reaction sequence leading to eventual hydrogen evolution. The corrosion mechanism involves both activation and diffusion processes. A rotating disc electrode in combination with ac techniques and the enzyme carbonic anhydrate II, EC 4.2.1.1, were used to characterise the diffusion effects. A chemical–electrochemical cathodic reaction mechanism is proposed.     

Electrochemical behaviour of low carbon steel in concentrated carbonate chloride brines

The polarization curves of low carbon steel in deaerated carbonate bicarbonate buffers (pH 10.3) show three distinct regions: (a) an active region characterized by a Tafel slope of 125 ± 5 mV which is independent of the chloride concentration, (b) a gradual active to passive transition, and (c) a broad passive region. The addition of NaCl has a stronger effect on the passive than on the active region. For NaCl concentrations of 0.1 to 2 M, NaCl has only a small promoting effect (a reaction order of 0.1) on the anodic dissolution of the steel in the active region. Measurements of electrochemical impedance under free corrosion conditions confirm the above findings. The results are explained in terms of the more favourable formation of an iron hydroxy-carbonate complex (called green rust carbonate) than the formation of the corresponding green rust chloride complex. Passivity is attributed to the formation of a protective film containing both FeOOH and Fe₂O₃. It deteriorates with increasing chloride concentration and potential and improves with increase of buffer concentration. Evidence is also presented for metastable pitting, particularly in the presence of the lower chloride concentration, for example, 0.1, 0.2 and 0.5 M NaCl.     

Electrochemical study on the effect of bipyridine dicarboxylic acid and its cobalt complex on the corrosion behaviour of carbon steel in acidic medium

The 2,2′-bipyridine-3,3′-dicarboxylic acid (bida) and its cobalt complex (Co-bida) were tested as corrosion inhibitors for N80 carbon steel in sulphuric acid solution by electrochemical polarization and electrochemical impedance spectroscopy method. The results indicate that the complex and ligand inhibit the corrosion of mild steel in H₂SO₄ solutions and the extent of inhibition increases with inhibitor concentration and decreases with temperature. The inhibition efficiency of the inhibitors follows the trend Co-bida > bida. A mixed-inhibition mechanism is proposed for the inhibitive effects of the compounds. The adsorption characteristics of the inhibitors were approximated by Temkin isotherm. Morphological study of the carbon steel electrode surface was undertaken by scanning electron microscope and the interfacial species formed on the surface in the presence of inhibitors analyzed by infrared spectroscopy.     

Influence of temperature, chloride ions and chromium element on the electronic property of passive film formed on carbon steel in bicarbonate/carbonate buffer solution

The influences of temperature, chloride ions and chromium element on the electronic property of passive film formed on carbon steel in NaHCO₃/Na₂CO₃ buffer solution are investigated by capacitance measurement and electrochemical impedance spectroscopy (EIS). The results show that the passive film appears n-type semiconductive character; with increasing the solution temperature, the addition of chromium into carbon steel and increasing the concentration of chloride ions, the slopes of Mott–Schottky plots decrease, which indicates the increment of the defect density in the passive film. EIS results show that the transfer impedance R₁ and the diffusion impedance W decrease with increasing the solution temperature, with the addition of chromium into carbon steel and with increasing the chloride ions concentration. It can be concluded that the corrosion protection effect of passive film on the substrate decreases with increasing the solution temperature, adding chromium into carbon steel and increasing chloride ions concentration.     

Effect of molecular chlorine diffusion on theoretical potential-current density relations for chlorine evolving electrode

The effect of molecular chlorine diffusion upon the theoretical potential-current density relations was calculated for chlorine evolution according to the Volmer—Tafel mechanism as well as the Volmer—Heyrowsky mechanism. It has been found that a minimum Tafel slope of 29.6 mV at 298 K occurs for both mechanisms. This slope occurs for the Volmer—Tafel mechanism when either the Tafel reaction or the chlorine diffusion, away from the electrode surface into the bulk of solution, is the rate-determining step, and for the Volmer—Heyrowsky mechanism when it is the chlorine diffusion that is the rate-determining step.Moreover, it has been established that only a careful use of both the polarization resistance at the reversible potential and the stoichiometric number from this deduced, is allowed to elucidate the mechanism of electrode reactions with adsorbed atomic intermediates.     

Effect of steel microfibers on corrosion of steel reinforcing bars

Steel microfiber reinforcement was previously found to be successful in mitigating alkali silica reaction in concrete, an expansive phenomenon. The use of steel microfibers to mitigate rebar corrosion, another expansive reaction, was investigated. Mortar specimens with and without steel microfiber reinforcement were exposed to a corrosive environment. All specimens were prepared with water/cement ratios of both 0.40 and 0.55, cured for 28 days, and then submerged in aerated 3.5% NaCl solution. The corrosion behavior of the specimens was monitored via electrochemical measurements. Three types of electrochemical tests were performed: corrosion potential measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy. Chloride concentration measurements and microscopic analysis were performed as well. The polarization curves, Tafel, and polarization resistance measurements indicate that the steel rebar in the microfiber-reinforced mortars are more resistant to corrosion than the rebar in the control mortars, despite higher chloride concentrations. Furthermore, the steel microfiber-reinforced cement based materials have a lower electrolytic resistance. This is not indicative of a higher corrosion rate, which would be the case if it had been observed in standard mortar specimens.     

Kinetics of hydrogen evolution reaction on a stainless steel electrode

The kinetic parameters for the hydrogen evolution reaction on a stainless steel substrate have been obtained from a study of the steady-state polarization curves as well as the galvanostatic transients. The high Tafel slope obtained in the steady-state polarization measurements was ascribed to the presence of an oxide film present on the surface of the stainless steel electrode.     

THE EFFECT OF ENVIRONMENTALLY BENIGN FRUIT EXTRACT OF SHAHJAN (MORINGA OLEIFERA) ON THE CORROSION OF MILD STEEL IN HYDROCHLORIC ACID SOLUTION

The inhibition of the corrosion of mild steel in hydrochloric acid solution by the fruit extract of shahjan (Moringa oleifera) was studied using weight loss, electrochemical impedance spectroscopy (EIS), linear polarization, and potentiodynamic polarization techniques (Tafel). Inhibition was found to increase with increasing concentration of the extract. The effect of temperature, immersion time, and acid concentration on the corrosion behavior of mild steel in hydrochloric acid solutions with addition of extract was also studied. The inhibition occurred via adsorption of the inhibitor molecules on the mild steel surface obeying the Langmuir adsorption isotherm. Thermodynamic activation parameters such as activation energy, enthalpy (ΔH*), and entropy (ΔS*) of activation for corrosion process were calculated and discussed. The results obtained show that both chemical and physical adsorption of inhibitor molecules occur simultaneously and the fruit extract of shahjan (Moringa oleifera) could serve as an effective inhibitor of the corrosion of mild steel in hydrochloric acid media.     

Electropolymerization of poly(N-ethyl aniline) on mild steel: Synthesis, characterization and corrosion protection

Poly(N-ethylaniline) (PNEA) coatings on the mild steel electrode were synthesized by electrochemical oxidation of N-ethylaniline using aqueous oxalic acid solutions as reaction medium. Electrodeposition was carried out by potentiodynamic, potentiostatic and galvanostatic synthesis techniques. Smooth, adhesive and thick PNEA coatings on mild steel could be electrosynthesized during sequential scanning of the potential region between −0.5 and 1.4 V versus SCE, with scan rate of 20 mV s⁻¹. The electrodeposited coatings were characterized by cyclic voltammetry, FT-IR and UV-vis techniques. Corrosion behavior of PNEA coated steels was investigated by linear anodic potentiodynamic polarization technique and Tafel test. Anodic potentiodynamic polarization results showed that electrodissolution current value of PNEA coated steel decreased about 90% compared to that of the uncoated steel in 0.5 M H₂SO₄ aqueous solution. Tafel plots showed also strong decrease of corrosion current for the PNEA coated electrode compared to the uncoated steel electrode in 3% NaCl as corrosive medium.     

Sur le choix d'un critère de determination de la vitesse de corrosion d'un acier au carbone dans une solution à 3% de chlorure de sodium aérée et agitée

Résumé A l'aide d'une électrode à disque tournant en acier au carbone, on a effectué des tracés potentiostatiques de courbes courant-potentiel cathodiques et des mesures de résistance de polarisation, dans une solution à 3% aérée et agitée de chlorure de sodium. On montre de cette façon que le contrôle de la corrosion, purement diffusionnel dans le domaine des vitesses de rotation relativement basses de l'électrode, devient mixte, c'est-à-dire d'activation-diffusion, aux vitesses plus élevées. Il s'ensuit que, dans le premier cas, l'intensité de corrosion peut être donc considérée comme égale au courant limite de diffusion de l'oxygène dissous; par contre, dans le second cas, les vitesses de corrosion déterminées par extrapolation au potentiel de corrosion des droites de Tafel corrigées de la diffusion sont en bon accord avec celles obtenues par d'autres méthodes, en particulier une méthode de mesure directe (dosage du fer passé en solution).

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Plotting of steady-state cathodic polarization curves and polarization resistance measurements was carried out in an aerated and stirred 3 wt% NaCl solution using a carbon steel rotating disc electrode. Under these conditions, it is shown that the corrosion process which is controlled only by convective diffusion at relatively low rotation speeds, attains mixed kinetics, i.e. activation-diffusion control, at higher rotation speeds. In the first case, the corrosion rate can be considered equal to the limiting diffusion current of dissolved oxygen; in the second case, the corrosion rates determined by extrapolation to the corrosion potential of the diffusion corrected Tafel line are in good agreement with those determined by other methods, particularly by titration of dissolved iron.

     

镀锌层单宁酸钝化膜的耐蚀性

为提高镀锌层的耐蚀性,以氟钛酸钾、双氧水、硝酸为辅助成分,制备了单宁酸钝化液,并对低碳钢上的碱性镀锌层进行了钝化处理.通过质量分数为5%的NaCl溶液浸泡试验,确定了最佳钝化液组成和钝化工艺条件为:单宁酸40 g/L,HNO3 5 mL/L,氟钛酸钾10g/L,H2O2 60 mL/L,温度25℃,时间20～30 s....     

THE ROLE OF PHOSPHONATE DERIVATIVES ON THE CORROSION INHIBITION OF STEEL IN HCL MEDIA

The inhibition of corrosion of steel by two P-containing compounds, sodium methyldodecyl phosphonate and sodium methyl (11-smethacryloyloxyundecyl) phosphonate, in hydrochloric acid has been investigated at various temperatures using electrochemical techniques (impedance spectroscopy (EIS), potentiodynamic polarization) and weight loss measurements. Inhibition efficiency (E%) increased with phosphonate concentration. Adsorption of inhibitors on the steel surface in 1 M HCl follows the Langmuir isotherm model. EIS measurements showed that the dissolution process of steel occurred under activation control. Polarization curves indicated that inhibitors tested acted as cathodic inhibitors. The temperature effect on the corrosion behavior of steel in 1 M HCl without and with the inhibitor was studied in the temperature range from 313 to 353 K. The adsorption free energy and activation parameters for the steel dissolution reaction in the presence of phosphonates were determined.     

Effect of pyridine and its derivatives on the electrodeposition of nickel from aqueous sulfate solutions. Part II: Polarization behaviour

The electrochemical reactions occurring during electrodeposition of nickel from acidic sulfate solutions were examined by cyclic and linear sweep voltammetry techniques. The effect of pyridine, 2-picoline and 4-picoline on the electrode polarization behaviour and electron transfer parameter of the cathodic reduction process was also investigated. Strongest electrode polarization was seen with 4-picoline. The order of cathodic polarization was 4-picoline > 2-picoline > pyridine. Kinetic parameters such as Tafel slope, transfer coefficient and exchange current density were determined to analyse the nature of the electrode reactions. The exchange current density for nickel deposition on nickel and stainless steel substrates was in the order 4-picoline < 2-picoline < pyridine.     

THE ROLE OF PHOSPHONATE DERIVATIVES ON THE CORROSION INHIBITION OF STEEL IN HCL MEDIA

The inhibition of corrosion of steel by two P-containing compounds, sodium methyldodecyl phosphonate and sodium methyl (11-smethacryloyloxyundecyl) phosphonate, in hydrochloric acid has been investigated at various temperatures using electrochemical techniques (impedance spectroscopy (EIS), potentiodynamic polarization) and weight loss measurements. Inhibition efficiency (E%) increased with phosphonate concentration. Adsorption of inhibitors on the steel surface in 1 M HCl follows the Langmuir isotherm model. EIS measurements showed that the dissolution process of steel occurred under activation control. Polarization curves indicated that inhibitors tested acted as cathodic inhibitors. The temperature effect on the corrosion behavior of steel in 1 M HCl without and with the inhibitor was studied in the temperature range from 313 to 353 K. The adsorption free energy and activation parameters for the steel dissolution reaction in the presence of phosphonates were determined.