Corrosion mechanism of pure aluminium in aqueous alkaline solution

The corrosion of pure aluminium in alkaline solution has been explored using an open circuit potential transient, potentiodynamic polarization experiment and a.c. impedance spectroscopy. The steady-state value of the open circuit potential (E _ocp ^ss ) of pure aluminium in alkaline solution was observed to decrease with increasing rotation rate of the specimen, which is ascribed to the enhanced anodic reaction. The extent of anodic polarization for the aluminium dissolution reaction on pure aluminium at E _ocp ^ss was found to be greater than that of cathodic polarization for the water reduction reaction. This indicates that the rate of corrosion of pure aluminium is mainly determined by the anodic reaction in alkaline solution. Based upon the experimental results, a corrosion mechanism for pure aluminium has been proposed in the presence of the native surface oxide film in alkaline solution, involving consecutive oxide film formation and dissolution, and simultaneous water reduction.     

Estimation of Corrosion Rate of Bulk and Powder Ni–Re Alloy

The corrosion current density of Ni–Re alloy (15.8 wt % Re) was estimated using recently developed method of compensating additives. The alloy was fabricated by the electrodeposition in the form of bulk specimen and the powder prepared of this specimen. The electrodeposition was performed in stirred 5 × 10^–3 M HCl solution. The method enabled us to determine the corrosion rate with no external polarization of studied specimens and at virtually constant pH value. A specific electrochemical activity of powder surface was estimated by comparing the corrosion currents of bulk and powder specimens. The powder was intended for testing its catalytic activity in several electrochemical reactions.     

Effect of acidity level Ro(H) on the corrosion of steel in concentrated HCL solutions

The corrosion of a carbon steel in (0.5 – 9.0 M) HCl media using weight loss, electrochemical polarization and polarization resistance measurements was investigated. The corrosion data are discussed as function of the Strehlow acidity function R_o(H) which is the extension of pH in concentrated solutions. Weight loss, corrosion current densities and resistance polarization values show a linear behaviour with the R_o(H) acidity function. The corrosion potential-R_o(H) plot is also linear using the ferricinium (Fc⁺) / ferrocene (Fc) reference electrode in concentrated acid solutions.     

Electrochemical studies on the interaction of l-cysteine with metallic copper in sulfuric acid

Amino acids have been widely used as green corrosion inhibitors for an array of metals. Considering its importance in corrosion chemistry, studies were undertaken with the objective to discovering the inhibitory effect of a sulfur-containing amino acid, l-cysteine, on copper in different concentrations of sulfuric acid (0.5, 1.0, and 1.5 M) at different temperatures. Techniques like the weight loss method, electrochemical impedance spectroscopy, potentiodynamic polarization (Tafel), and adsorption studies were employed. Results revealed that l-cysteine do offer an attractive inhibition efficiency. However, with an increase in the concentration of the inhibitor, corrosion rates decreased irrespective of the temperature gradients. This is due to surface adsorption of the inhibitor molecules on the metal which has contributed to a decreased double-layer capacitance and increased polarization resistance. With the increase in the concentration of the medium, the corrosion rate was also enhanced and this is due the liberation of a high quantum of H⁺ ions. Based on the results of Tafel polarization studies, it is evident that the amino acid, l-cysteine, could act as a mixed type inhibitor. The importance of l-cysteine in the corrosion of copper metal has been highlighted in this paper.     

Inhibitive effect of imidazopyridine derivative towards corrosion of C38 steel in hydrochloric acid solution

The effect of adding 2-phenylimidazo[1,2-a]pyridine-3-carbaldehyde derivative named (P2), newly synthesized on the electrochemical behavior of C38 steel in molar hydrochloric acid was investigated by using the weight-loss method, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) measurements. EIS results show that the transfer resistance increases with the increase of concentration of P2 and it also had an inhibiting effect on C38 steel corrosion in HCl solutions. Weight-loss essays confirm that the corrosion rate decreases as the P2 concentration increases. The inhibition efficiency for this compound studied increased with the increase in the inhibitor concentrations to attain 91.7 % at the 10^?3 M of P2. The potentiodynamic polarization curves indicated that P2 acted as a mixed-type inhibitor in hydrochloric acid.     

嘧啶衍生物对钢在盐酸溶液中的缓蚀作用

采用失重法、动电位极化曲线、电化学阻抗谱(EIS)、量子化学计算研究了两种嘧啶衍生物(2-羟基嘧啶(HP)和2-巯基嘧啶(MP))在1.0-5.0 mol·L^-1 HCl溶液中对冷轧钢(CRS)的缓蚀作用. 结果表明: HP和MP在1.0 mol·L^-1 HCl溶液中对冷轧钢具有良好的缓蚀作用, 且在钢表面的吸附符合Langmuir吸附等温式. 缓蚀率随缓蚀剂浓度的增加而增大, 但随盐酸浓度的增加而减小.求出了相应的吸附热力学参数(吸附平衡常数(K),吸附自由能(ΔG⁰))和腐蚀动力学参数(表观活化能(E_a)、指前因子(A)、腐蚀速率常数(k)、动力学常数(B)), 并根据这些参数讨论了缓蚀作用机理. 动电位极化曲线表明, MP和HP均为混合抑制型缓蚀剂; EIS谱呈单一容抗弧,电荷转移电阻随缓蚀剂浓度的增加而增大. 两种嘧啶化合物的缓蚀率排序为MP>HP. 量子化学计算结果表明,MP比HP更具吸附活性,缓蚀性能的理论计算和实验结果相一致.     

Effect of sodium vanadate on corrosion of AD31 aluminum alloy in acid media

Scanning electron microscopy, potentiodynamic polarization method, and electrochemical impedance spectroscopy were used to study the corrosion behavior of AD31 (AA6063) aluminum alloy in acid (pH 3) 0.05 M NaCl solutions containing 3 mmol dm^–3 of NaVO₃ inhibitor. It was found that the corrosion of AD31 alloy in acid sodium chloride solutions predominantly occurs locally at aluminum/intermetallic particle phase boundaries and is limited by the electrochemical stage of charge transfer. It was shown that introduction of sodium vanadate can reduce the rate of selective dissolution of magnesium from the alloy and provides a protective effect on the level of 7–10%.     

Corrosion and biological behavior of nanostructured 316L stainless steel processed by severe plastic deformation

Nanostructured metals have different mechanical, chemical, and physical behaviors in comparison with the microstructured ones. Numerous research studies demonstrated that the biological behavior of nanostructured metallic implants was improved significantly. Concerning the nanostructured metals, decreasing the corrosion rate and the releasing of hazardous ions from metallic implants, and thus increasing the biocompatibility of implants are due to improving the native oxide layer. In the present study, nanostructured 316L stainless steel (biomedical grade) was manufactured via equal channel angular pressing (ECAP) method. To do so, the 316L stainless steel (SS) was exposed to the ECAP operation for eight passes. The impact of the ECAP process on corrosion behavior of SS samples was evaluated through performing the electrochemical polarization corrosion tests in Ringer's solution. Scanning electron microscopy was employed to study the surface morphology of common SS and ECAPed SS sample after the electrochemical polarization tests. Moreover, the biological behavior of the samples was evaluated via cell culture using fibroblast cells. The corrosion test results revealed a substantial decrease of corrosion rate from 3.12 (coarse‐grained sample) to 0.42 μA cm^?2 (for nanostructured). Furthermore, the cell proliferation in the interface of nanostructured sample and cell culture medium enhanced dramatically compared with the coarse‐grained one. The much better biological behavior of nanostructured SS sample in comparison with the coarse‐grained one is mostly due to the significant decrease of corrosion rate on the surface of SS samples, and the presence of much more chrome oxide on the surface of SS sample. Copyright © 2015 John Wiley & Sons, Ltd.     

Influence des chlorures et des sulfures sur la corrosion des alliages inoxydables en milieu phosphorique

The corrosion resistance of stainless alloys has been studied in 40 % phosphoric acid contaminated by chlorides and/or sulfides. The influence of temperature and impurities on the behaviour of materials was clarified by using electrochemical techniques (polarization curves). The action of Cl⁻ ions results in the local destruction of the passivity layer whereas the S²⁻ ions induce an important incease in the corrosion rate. The simultanous presence of chloride and sulfide ions increases the agressivness of the phosphoric acid medium as a result of a synergic effect.     

Corrosion behaviour of SiC and Al2O3 reinforced Al 7075 hybrid aluminium matrix composites by weight loss and electrochemical methods

The corrosion study of Al 7075 hybrid metal matrix composites reinforced with equal weight percents (2.5, 5, 7.5, and 10) of silicon carbide and aluminium oxide is investigated in the present work by weight loss and electrochemical methods. In this study, composite specimens prepared by the squeeze casting technique were analyzed at room temperature to estimate the rate of corrosion in a 3.5% NaCl solution for various intervals using the weight loss method. As a consequence, a hybrid Al7075 composite reinforced with 10% SiC and 10% Al₂O₃ had a lower corrosion rate of 0.9997 mmpy than pure Al7075, which had a maximum corrosion rate of 3.4481 mmpy. The corrosion rate of hybrid composites is determined by the tafel polarization method and the electrochemical impedance spectroscopic method. These experiments showed that the corrosion rate of the hybrid metal matrix composite Al7075 + 10% SiC +10% Al₂O₃ was 0.630 mmpy less than that of the monolithic 7075 alloy. The corrosion morphology behaviour of the Al 7075 and their hybrid composite samples is observed by SEM. The SEM micrographs implied that SiC and Al₂O₃ reinforcements with the matrix alloy produced good interfacial and intermetallic bonding and hence decreased the corrosion rate.     

Electropolymerized coatings of polyaniline on copper by using the galvanostatic method and their corrosion protection performance in HCl medium

The synthesis of polyaniline coatings on the copper (Cu) surface has been investigated by using the galvanostatic method. The synthesized coatings were characterized by Fourier transform infrared spectroscopy, UV–visible absorption spectrometry and scanning electron microscopy. The anticorrosion performances of polyaniline coatings were investigated in 0.5 M HCl medium by the potentiodynamic polarization technique and electrochemical impedance spectroscopy. The corrosion rate of polyaniline‐coated Cu was found to be ～27 times lower than bare Cu, and potential corrosion increased from ?0.21 V versus Ag/AgCl for uncoated Cu to ?0.19 V versus Ag/AgCl for polyaniline‐coated Cu electrodes. Electrochemical measurements indicate that polyaniline coating has good inhibiting properties with a mean efficiency of ~96% at 10 mAcm^?2 current density applied on Cu corrosion in acid media. The results of this study clearly ascertain that the polyaniline has an outstanding potential to protect Cu against corrosion in an acidic environment. Copyright © 2014 John Wiley & Sons, Ltd.     

Inhibition de la corrosion du cuivre en milieu HCl 0,5 M par les composes organiques de type triazole

Some triazole-type organic compounds were tested as corrosion inhibitors for copper in 0.5 M HCl solution at 20°C. Electrochemical (potentiodynamic polarization and polarization resistance measurements) and gravimetric methods were used for this study. The obtained results showed that 3-amino-1,2,4 triazole (ATA) and 3,5 diamino-1,2,4 triazole (DTA) effectively reduce the corrosion rate of copper. The inhibition efficiency (E%) of these compounds increases with their concentrations and attains maximum values at 10⁻³M and 10⁻⁴ for ATA and DTA, respectively. The variation of efficiency with logC shows that these inhibitors are adsorbed on the metallic surface according to the Frumkin adsorption isotherm model.     

Magnesium-zinc-graphene oxide nanocomposite scaffolds for bone tissue engineering

The aim of this study was to fabricate and evaluate magnesium-zinc-graphene oxide nanocomposite scaffolds for bone tissue engineering. For this reason, Mg-6Zn, Mg-6Zn-1GO, and Mg-6Zn-2GO scaffolds were fabricated by the powder metallurgy method. The porosity level and also the pore size of the scaffolds were evaluated by SEM which varied from 40 to 46% and 200 to 500 μm, respectively. The chemical composition and microstructure of the scaffolds were characterized by XRD and SEM equipped with EDS; the presence of Mg, Zn, C, and O elements in the structure of the scaffolds was shown. Also, the elemental map confirmed the existence of magnesium, zinc, carbon, and oxygen in the structure of the scaffold. The mechanical properties of the scaffolds were investigated by the compression test; the results showed that by the addition of graphene oxide to the structure, the compressive strength of the samples increased from 5 to 8 MPa. Electrochemical corrosion polarization tests were conducted to evaluate the corrosion resistance of the samples immersed in simulated body fluid (SBF). Furthermore, the biodegradability of the scaffolds was determined by immersion of the samples in phosphate-buffered saline (PBS). The results demonstrated that the polarization resistance value and the corrosion rate for different formulations including Mg-6Zn, Mg-6Zn-1GO, and Mg-6Zn-2GO were 41.58, 35.48, and 55.40 Ω.cm² followed by 10.60, 14.83, and 9.06 mm.year^?1, respectively. Based on the results, the Mg-6Zn-2GO formulation presented the best corrosion resistance among the samples were investigated, which confirmed the results of the immersion test. Moreover, the MTT assay proved that the extract of Mg-6Zn-2GO scaffolds was not cytotoxic in contact with L-929 cells which validated the studied scaffolds for bone tissue applications.     

Spectral and thermal studies of 4-(phenyldiazenyl)phenyl 2-furoate as corrosion inhibitor for carbon steel

The azo-ester, namely 4-(phenyldiazenyl)phenyl 2-furoate (PPF) by a coupling reaction between 4-(phenyldiazenyl)phenol and 2-furoyl chloride in the presence of pyridine was obtained. For characterization of this compound UV–Vis, FTIR, and thermal analysis were used. PPF was investigated as corrosion inhibitor for carbon steel in saline waters using potentiodynamic polarization. Morphology of the surface before and after corrosion was examined by optical microscopy. Potentiodynamic polarization shows that the corrosion current densities decrease and values of polarization resistance and inhibition efficiency increase with PPF concentration reaching a maximum of 89.6 %, at 0.1 mmol L^?1.     

Modeling of corrosion inhibition of copper-nickel alloy in hydrochloric acid by benzotriazole

The corrosion inhibition of copper-nickel alloy by benzotriazole (BTA) in 1.5 M HCl has been investigated by weight loss and polarization techniques at different temperatures. Maximum value of inhibitor efficiency was 99.8% at 35°C and 0.1 M inhibitor concentration, while the lower value was 86.3% at 65°C and 0.02 M inhibitor concentration. The activation energy values were higher in presence of BTA which indicate that in presence of inhibitor, corrosion reaction requires more energy to occur. Two mathematical models were used to represent the weight loss corrosion rate data with high correlation coefficients. Electrochemical polarization measurements showed that BTA is a mixed type inhibitor.     

Experimental and theoretical studies of carbon steel corrosion protection in phosphoric acid solution by expired lansoprazole and rabeprazole drugs

The effects of expired lansoprazole and rabeprazole on the corrosion protection of carbon steel in phosphoric acid (3.0 ?M) solution were examined by Tafel polarization and electrochemical impedance spectroscopy (EIS). Lansoprazole and rabeprazole concentrations (0.5, 1.0, 5.0 and 10 ?mM) in acid solution were raised, which improved corrosion prevention. Both lansoprazole and rabeprazole as the mixed inhibitors retarded the anodic and cathodic processes, as indicated by polarization data. With the increasing temperature in the range of 25–55 ?°C, the inhibition efficiency drops from 92.9% to 69.3% for lansoprazole and from 94.8% to 74.2% for rabeprazole. The major decrease in the inhibition efficiency with ascending temperature proved the physisorption of the drugs. The activation energies for carbon steel corrosion in H₃PO₄solution were enhanced from 41.6 ?kJ ?mol^?1 to 81.9 ?kJ.mol^?1and 85.9 ?kJ ?mol^?1 for lansoprazole and rabeprazole, respectively. The influence of temperature on the corrosion process of carbon steel in the acid medium was used to derive the thermodynamic quantities of corrosion. The adsorption of both lansoprazole and rabeprazole on carbon steel followed the Langmuir adsorption isotherm. The polarization data yielded outcomes that were consistent with the results arising from impedance measurements. The theoretical study of both lansoprazole and rabeprazole was done by a density functional theory (DFT) approach to realize the effects of molecular structure on their inhibitive action. Both lansoprazole and rabeprazole contain a higher E_HOMO, a lower E_LUMO and a lower energy gap than some inhibitors earlier reported as good corrosion inhibitors in the literature.     

Evaluation of reinforcement corrosion rate in concrete structures by electrochemical noise measurements

Experimental results on the polarization resistance estimation in a three-electrode setup that consists of two carbon steel electrodes and the silver reference electrode are presented. The corrosion rate varies with the conditions changing inside the concrete structure due to its irregular wetting in an aqueous solution of NaCl. The change of polarization resistance of a single steel electrode can be identified by voltage and current electrochemical noise measurements. The observed change does not exceed the factor of a few times of the originally recognized value. The newly proposed method of electrochemical noise analysis for monitoring of swift corrosion rate changes is presented in detail. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 5, pp. 611–616. The text was submitted by the authors in English.     

Effect of pulegone and pulegone oxide on the corrosion of steel in 1?M HCl

The inhibitive action of pulegone and pulegone oxide toward acid corrosion of steel in molar hydrochloric acid was studied by weight loss measurements, potentiodynamic polarization, and impedance spectroscopy (EIS) methods. The pulegone is extracted starting from oil of Pennyroyal Mint (Mentha pulegium). The natural compound was found to delay the corrosion rate. The pulegone oxide is prepared by oxidation of pulegone. The inhibition efficiency was found to increase with the inhibitor content to attain 81 and 75% at 5 g dm⁻³ for pulegone and pulegone oxide. The increase in temperature leads to an increase in the inhibition efficiency of the natural compared.     

镁合金表面原位生长有机膦酸盐薄膜及耐蚀行为

利用超声辅助的浸渍涂布方法,在AZ91D镁合金表面原位生长了氨基二乙酸亚甲基膦酸镁铝薄膜,其中包含具有纳米尺度的变形六边形板状颗粒。塔菲尔极化曲线、电化学阻抗谱测量表明,修饰后的AZ91D镁合金的耐腐蚀行为依赖于浸渍所用的膦酸浓度、pH值、温度及时间等。在3.5%NaCl溶液中,未修饰的AZ91D其腐蚀活化能是18.1 kJ.mol-1,而在1.5 mmol.L-1膦酸溶液中pH值分别是1.7、11.5时浸渍涂布有机膦酸盐薄膜后,AZ91D的腐蚀活化能分别是27.9、37.8 kJ.mol-1。     

Extracts of Punica granatum Linne husk as green and eco-friendly corrosion inhibitors for mild steel in oil fields

Extracts of pomegranate have been investigated, by use of weight loss and potentiodynamic polarization techniques, as green and eco-friendly inhibitors of corrosion of Q235A steel in 1 M hydrochloric acid solution at 60 °C. The efficiency of inhibition by the extracts varied with extract concentration from 10 to 1,000 mg/L; the highest efficiency was 95.0 %. The extracts inhibit corrosion mainly by an adsorption mechanism. In addition, the hydroxyl and ether groups of polyphenols can capture the H⁺ to reduce the corrosion, and the polyphenols can eliminate dissolved O₂ to inhibit oxygen-adsorption corrosion. Potentiodynamic polarization studies show that extracts are mixed-type inhibitors.