The litchi (Litchi Chinensis) peels extract as a potential green inhibitor in prevention of corrosion of mild steel in 0.5 M H2SO4 solution

The corrosion inhibition of mild steel in 0.5 M H₂SO₄ solution by the extract of litchi peel (Litchi chinensis) was studied by weight loss method, potentiodynamics polarization and electrochemical impedance spectroscopy (EIS). The results show that the litchi peels extract acts as mixed-type inhibitor. The inhibition of corrosion is found to be due to adsorption of the extract on metal surface, which is in conformity with Langmuir’s adsorption isotherm. UV–Vis, Fourier transform infrared (FT-IR) spectroscopy and Scanning electron microscopy (SEM) studies confirm that the inhibition of corrosion of mild steel occurs through adsorption of the inhibitor molecules.     

Corrosion behavior of AZ91D magnesium alloy in distilled water

The corrosion of AZ91D magnesium alloy has received extensive attention due to the continuous expansion of its application field in recent years. However, the corrosion of AZ91D magnesium alloy in distilled water is relatively few. In this paper, the corrosion behavior of AZ91D magnesium alloy was studied in distilled water by electrochemical tests in combination with weight loss and surface analysis methods. The results indicated that the corrosion rate of AZ91D magnesium alloy increased with the increase of temperature and immersion time. The increase of the corrosion rate of AZ91D magnesium alloy with the increase of immersion time might be attributed to the damage of the structure of corrosion product film by hydrogen evolution, significantly accelerating the anodic process of AZ91D magnesium alloy. It was interesting that, in distilled water, the EIS of AZ91D magnesium alloy excluded an inductive arc in the low frequency region, which indicated that there was no the adsorption and desorption of aggressive ions or the damage and repair of film. The corrosion product film of AZ91D magnesium alloy in distilled water was composed of a compact inner corrosion product film and a loose outer corrosion product film.     

阳极氧化AZ91D镁合金在氯化钠稀溶液中的腐蚀行为

利用盐雾实验、极化曲线扫描、电化学阻抗谱和电化学噪声技术等电化学研究方法结合扫描电镜表面观测技术对AZ91D镁合金氧化膜在1%(w)氯化钠溶液中的耐蚀性能进行了评价. 结果表明, 氧化前后的镁合金腐蚀行为发生明显改变, 如未封孔的阳极氧化膜耐中性5%氯化钠盐雾试验时间超过200 h; 氧化后的镁合金自腐蚀电位明显正移, 点蚀诱导期延长; 阳极氧化膜的高频阻抗约为裸露镁合金的数千倍, 这些变化证明阳极氧化处理使镁合金获取了十分优异的耐蚀性能. 首次利用分形维数Df的变化规律初步描述氧化后AZ91D镁合金的腐蚀过程. 可以发现随着浸泡时间的延长, Df呈现出初期快速增长, 随后出现波动, 最后稍有降低的变化过程. 这种现象对应于氧化后AZ91D 镁合金在1%氯化钠溶液中腐蚀的三个阶段.     

AZ31镁合金表面聚吡咯的化学氧化合成及其耐蚀性能

以对甲苯磺酸钠为掺杂剂, 三氯化铁为氧化剂, 用化学氧化聚合法在AZ31 镁合金表面制备聚吡咯(PPy)膜. 采用傅里叶变换红外(FTIR)光谱分析了镁合金表面聚吡咯膜结构, 通过电化学极化曲线、电化学阻抗谱(EIS)研究了其耐蚀性能, 通过扫描电子显微镜(SEM)、X射线能量散射谱(EDS)分析了表面形貌和成分. 和镁合金裸样相比, 聚吡咯膜对镁合金腐蚀有一定的抑制作用. 硅烷预处理改善了镁合金/聚吡咯体系的耐腐蚀性能, 使腐蚀电位较镁合金裸样正移了110 mV, 电流密度减小了约2个数量级.     

Surface characteristics of AZ91D alloy anodized with various conditions

Anodic oxidation of an AZ91D magnesium alloy was carried out in an attempt to increase the corrosion resistance. The alloy was placed in an electrolyte containing 0.1 M sodium silicate (Na₂SiO₃), 2.0 M sodium hydroxide (NaOH) and 0.1 M sodium phosphate (Na₃PO₄), and treated with a current density of 100–400 mA/cm² for 1 to 4 min. After the anodic oxidation treatment, the surface characteristics were analyzed by SEM, X‐ray diffraction (XRD) and a surface roughness tester. The corrosion resistance was determined by measuring the corrosion potential and corrosion current density using potentiodynamic polarization in a 3.5 wt% NaCl electrolyte solution. Although the anodic oxidation treatment with the base electrolyte resulted in an arrival voltage ranging from 60 to 70 V, the addition of silicate tended to reduce this arrival voltage by approximately 10–20 V and decrease the critical voltage required for the formation of a porous oxide film. The pore size and film thickness increased with increasing applied current and treatment time. The addition of silicate to the electrolyte resulted in films with a homogeneous pore size and a film thickness increasing with the increasing applied current and treatment time. XRD showed the formation of a new MgO and Mg₂SiO₄ phase. The formation of Mg₂SiO₄ was attributed to the presence of SiO₄^4? in the film. After the addition of silicate, the corrosion potential increased and corrosion current decreased, resulting in improved corrosion resistance. Copyright © 2008 John Wiley & Sons, Ltd.     

Employing electrochemical frequency modulation for studying corrosion and corrosion inhibition of copper in sodium chloride solutions

The inhibition effect of 2-carboxymethylthio-4-(p-methoxyphenyl)-6-oxo-1,6-dihy-dropyrimidine-5-carbonitrile (CPD) towards the corrosion of copper was studied in aerated stagnant 3.5% NaCl at 25 °C using ac techniques include electrochemical frequency modulation and electrochemical impedance spectroscopy as well as potentiodynamic polarization measurements. Corrosion rates determined using electrochemical frequency modulation (EFM) which measures the non-linear behaviour of a corroding system are compared with corrosion rates obtained from traditional electrochemical techniques and show good agreement. Data obtained from EIS were analyzed to model the corrosion inhibition process through equivalent circuit. Polarization measurements showed that CPD acts as mixed-type inhibitor. The inhibition efficiency increases with an increase in the concentration of CPD. The adsorption of the inhibitor on the copper surface in the sodium chloride solution was found to obey Langmuir’s adsorption isotherm. A mixed inhibition mechanism is proposed for the inhibitive effects of CPD as revealed by potentiodynamic polarization technique.     

十二烷基苯磺酸钠在AZ31镁合金表面的吸附及其缓蚀作用

采用电化学阻抗谱(EIS)和极化曲线研究十二烷基苯磺酸钠(SDBS)对AZ31镁合金在3.5%(w, 质量分数)NaCl腐蚀介质中的吸附行为及缓蚀作用. 结果表明: SDBS可有效抑制AZ31镁合金在NaCl介质中的腐蚀, 其浓度为0.008 mol·L-1时缓蚀效率可达90%以上; 升高温度并不利于提高SDBS的缓蚀效率. SDBS在AZ31镁合金表面主要发生物理吸附, 吸附过程为放热、熵增的自发过程, 近似符合Langmuir单分子层吸附模型; SDBS为混合抑制型缓蚀剂, 但主要抑制阳极反应.     

Experimental and theoretical studies of acridine orange as corrosion inhibitor for copper protection in acidic media

The corrosion process commonly limits the use of copper in practical applications. The use of corrosion inhibitors is one of the effective methods to reduce the corrosion rate of copper. In this research, the inhibition effect of acridine orange (3,6-bis(dimethylamine)acridine) (AcO) for the protection of copper in 0.5 ?M ?H₂SO₄ solution was studied. For this aim, the change of open circuit potential with exposure time (E_ocp-t), electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), anodic and cathodic potentiodynamic polarization measurements (PP) and chronoamperometry (CA) techniques were used. Some quantum chemical parameters (E_HOMO, E_LUMO and dipole moment) were calculated and discussed. The AcO film formed over the copper surface was examined by SEM, EDX, AFM and contact angle measurements. The electrochemical data showed that AcO is an effective corrosion inhibitor even at low concentrations (ranging between 99.1% and %99.4 ?at concentrations from 0.01 ?mM to 1 ?mM). The corrosion rate of copper decreases in the presence of the inhibitor by reducing both anodic and cathodic rates, which is depended on its concentration. This compound behaves as mixed-type corrosion inhibitors with predominantly cathodic type. Its adsorption on the copper surface obeys Langmuir adsorption isotherm. The value of adsorption equilibrium constant (K_ads) and the standard free energy of adsorption were ΔG_ads 1.298 x 10³ ?M^?1 and -27.71 ?kJ/mol in the case of 0.5 ?M ?H₂SO₄ solution containing 1.0 ?mM AcO, which shows the adsorption is high and spontaneous. The adsorbed inhibitor film over the metal increase contact angle of the surface, which suggests the more hydrophobic properties of the surface are increasing coming from the orientation of hydrophobic sites to the electrolyte. The zero charge potential (E_pzc) studies showed that the surface charge of the metal is positive in the corrosive media containing the inhibitor. Quantum chemical calculations showed that the binding of inhibitor molecules to the metal surface takes place through N atoms of the inhibitor.     

乌洛托品对模拟汽车冷却液中镁合金的缓蚀作用

镁合金具有高比强度、比刚度以及良好的铸造性、切削性、抗冲击减震性、导热性、无毒性和可回收性等优点,被认为是汽车工业中极好的铝合金及有色金属替代品[1]。用镁合金制造汽车部件,特别是发动机等大重量部件,可以大大减轻车身重量,进而降低能源消耗和废气污染。但是由于镁合     

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%.     

Extract sarampa wood (Xylocarpus Moluccensis) as an eco-friendly corrosion inhibitor for mild steel in HCl 1M

Plant extracts are currently being used as eco-friendly corrosion inhibitors. In this study, the inhibitive performance of Xylocarpus Moluccensis extract (XME) was used as an eco-friendly corrosion inhibitor for the first time. The extract was studied using electrochemical measurement on mild steel in 1M HCl. Results from FIR and phytochemical confirmed that Xylocarpus Moluccensis extract contains compound hydroxyl group, phenolic, and flavonoid content which can be used as a corrosion inhibitor. The inhibition efficiency was determined using Tafel polarization and electrochemical impedance spectroscopy and showed 68% efficiency in 500 ppm. Langmuir adsorption isotherm was used to determine the adsorption mechanism of XME. Surface characterization (AFM) was also used to study the surface morphology of protective film inhibitors.     

(NaPO3)6对AZ91D镁合金微弧氧化陶瓷层电化学腐蚀特性的影响

在Na2SiO3-KOH电解液体系中添加一定量的(NaPO3)6, 利用微弧氧化(MAO)技术在AZ91D 镁合金表面制备了原位生长的陶瓷层. 采用动电位极化和电化学阻抗谱(EIS)技术研究了添加(NaPO3)6前后, 制备的陶瓷层在3.5%(w) NaCl溶液中的室温电化学行为. 结果表明, 添加(NaPO3)6后, 陶瓷层的自腐蚀电位显著上升, 自腐蚀电流密度明显减小. 这主要是由于(NaPO3)6增加了反应过程中基体镁合金表面的“氧空位”和溶液中PO3-4的含量, 促使元素Mg在金属/膜层(M/F)界面上快速形成相应氧化物, 从而增加了陶瓷层的厚度和致密性. 根据电化学反应体系和陶瓷层的特殊结构, 建立了合理的等效电路, 并结合EIS 数据, 分析了添加(NaPO3)6提高陶瓷层耐电化学腐蚀性能的机理.     

Adsorption of Basic Magenta II onto H2SO4 activated immature Gossypium hirsutum seeds: Kinetics,isotherms, mass transfer,thermodynamics and process design

The adsorption of Basic Magenta II onto H₂SO₄ activated immature Gossypium hirsutum seeds was analysed using Ho, modified Freundlich, Sobkowsk–Czerwi, Blanchard, Elovich, Avrami, and modified Ritchie kinetic models by nonlinear regression-sum of normalized errors analysis. The goodness of fit was evaluated with coefficient of determination and root mean square error. The good agreement of experimental data to Avrami second-order model indicated that the mechanism of adsorption followed multiple kinetic orders. The Avrami second-order mechanism was applied to predict the rate constant of sorption and the equilibrium capacity and subsequently the obtained equilibrium adsorption capacities were utilized to find the equilibrium concentrations. Langmuir, Freundlich, Temkin, Sips and Hill isotherms were investigated to understand the nature of adsorption with the help of nonlinear regression analysis. Both Sips and Hill isotherms were best fit to the adsorption equilibrium data showing the homogeneous adsorption on the heterogeneous surface of carbon and the positive co-operative manifestations of the Basic Magenta II molecules. The mass transfer study depicted the details such as mass transfer coefficient, intra-particle diffusion rate, pore diffusion coefficient, and film diffusion coefficient. The adsorption process was found to be controlled by film diffusion. The thermodynamic parameters like, Gibbs free energy change, enthalpy change, entropy change and isosteric heat of adsorption confirmed the endothermic, feasible and spontaneous nature of adsorption. A single stage batch adsorber was designed using Sips isotherm constants to estimate the amount of carbon required for desired purification.     

Inhibition effect of environmentally benign Karanj (Pongamia pinnata) seed extract on corrosion of mild steel in hydrochloric acid solution

The inhibition of the corrosion of mild steel in hydrochloric acid solution by the seed extract of Karanj (Pongamia pinnata) has been studied using weight loss, electrochemical impedance spectroscopy, potentiodynamic polarization, and linear polarization techniques. 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 1 M HCl with addition of extract was also studied. The adsorption of the extract on the mild steel surface obeyed the Langmuir adsorption isotherm. Values of inhibition efficiency calculated from weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy are in good agreement. Polarization curves showed that Karanj (P. pinnata) seed extract behaves as a mixed-type inhibitor in hydrochloric acid. The activation energy as well as other thermodynamic parameters for the inhibition process was calculated. The adsorbed film on mild steel surface containing Karanj (P. pinnata) seed extract inhibitor was also measured by Fourier transform infrared spectroscopy. The results obtained showed that the seed extract of Karanj (P. pinnata) could serve as an effective inhibitor of the corrosion of mild steel in hydrochloric acid media.     

Surface morphological and impedance spectroscopic studies on the interaction of polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP) with mild steel in acid solutions

The inhibition of mild steel corrosion in aerated acid mixture of 0.5 N H₂SO₄ and 0.5 N HCl solution was investigated using potentiodynamic polarization studies, linear polarization studies, electrochemical impedance spectroscopy, adsorption, and surface morphological studies. The effect of inhibitor concentration on corrosion rate, degree of surface coverage, adsorption kinetics, and surface morphology is investigated. The inhibition efficiency increased markedly with increase in additive concentration. The presence of PEG and PVP decreases the double-layer capacitance and increases the charge-transfer resistance. The inhibitor molecules first adsorb on the metal surface following a Langmuir adsorption isotherm. Both PEG and PVP offer good inhibition properties for mild steel and act as mixed-type inhibitors. Surface analysis by scanning electron microscopy (SEM) and atomic force microscopy (AFM) shows that PVP offers better protection than PEG.     

Experimental and theoretical investigation of adsorption and inhibition properties of 2-Amino-1,3,5-triazine-4,6-dithiol against corrosion in hydrochloric acid solution on mild steel

In this work, 2-Amino-1,3,5-triazine-4,6-dithiol (2-ATD) as novel and high efficiency corrosion inhibitor has been investigated for mild steel (MS) corrosion in 0.5 M HCl solution using electrochemical methods, scanning electron microscopy (SEM), energy disperse X-ray spectroscopy (EDX), atomic force microscopy (AFM) and quantum chemical calculation methods. Potentiodynamic polarization (PDP) curves indicate that 2-ATD is mixed type inhibitor, corrosion inhibition efficiency increased with increasing inhibitor concentration and reached its value of 96.5%. Evolution of exposure time versus corrosion behavior of 2-ATD is examined in corrosive medium. While corrosion potential (E_corr) shifted more negative values, polarization resistances (R_p) decreased after 120 h exposure time due to the corrosion process. H₂ volume is measured in uninhibited and inhibited solutions (10 mM 2-ATD) after 120 h exposure time. Very low volume (3.6 mL cm⁻²) of H₂ is obtained on MS electrode in inhibited solution after 120 h of exposure, indicating that 2-ATD covers the entire surface against aggressive attack and retards the both anodic dissolution of MS and cathodic hydrogen evolution reactions. The adsorption process proposal is the Langmuir isotherm which is most suitable. Adsorption and thermodynamic parameters show that 2-ATD has a strong adsorption effect onto MS surface and includes mixed adsorption style (physical and chemical). Corrosion current density increases with increasing temperature and high activation energy (Ea) proves the strong adsorption of 2-ATD on the MS surface. Anti-corrosion mechanism of 2-ATD is described more detail with the potential of zero charge method. SEM, EDX and AFM analysis support the obtained results of electrochemical methods and confirm the existence of protective layer and strong adsorption of 2-ATD on the MS surface. Chronoamperometry test shows that current densities are almost constant whole experiment in the presence of organic film. Finally, quantum chemical calculation method of 2-ATD in blank solution is performed to investigate the active sites for possible attachment with MS surface.     

The interface electrochemical and chemical mechanism of a low alloy steel in a 3.5% NaCl solution containing Ce3+‐based inhibitor

The interface electrochemical and chemical mechanism of the low alloy steel in a 3.5% NaCl solution containing the Ce³⁺‐based inhibitor was investigated by the electrochemical techniques in conjunction with the surface analysis technologies. It was shown that the Ce^3+‐based inhibitor was an anodic inhibitor with more than 90.0% inhibitory efficiency. The net‐shaped inhibiting film with 200 to 500‐nm greyish balls was observed on the specimen surface. During the corrosion reaction occurred on the surface of the low alloy steel, the hydrolysis reaction of P₃O₁₀⁵⁻ and the disproportionation reaction of Ce³⁺ ions simultaneously occurred, too, resulting in the formation of the net‐shaped inhibiting film with nano‐scale greyish ball‐type products, which contained Ce element and had an obvious effect on the electrochemical process of the low alloy steel in a 3.5% NaCl solution containing the Ce³⁺‐based inhibitor. Therefore, the EIS spectra of the low alloy steel in a 3.5% NaCl solution containing the Ce³⁺‐based inhibitor were composed of a capacitive loop at a high‐frequency region and an inductive impedance loop at a low‐frequency region. The charge‐transfer resistance (R_t) increased with the immersion elapsed time, indicating that the inhibition efficiency of the Ce³⁺‐based inhibitor increased with immersion elapsed time. The calculated data based on the fitted electrochemical parameters showed the partial coverage of the inhibitor. This was further revealed by the analysis of electrochemical kinetics that the inductive impedance (L) loop at a low frequency region resulted from the localized absorption of the Ce³⁺‐based inhibitor on the surface of the low alloy steel in a 3.5% NaCl solution. It was also verified by micro‐morphologies.     

Ficus carica extract as environmentally friendly inhibitor for the corrosion of L-80 carbon steel in 0.5 ​M ​H2SO4 media

We reported here, the corrosion inhibition of carbon steel (CS) in H₂SO₄ media by Ficus carica leaves extract as green sustainable inhibitor. This study was investigated using mass loss method (ML), potentiodynamic polarization (PDP), electrochemical frequency modulation (EFM) and electrochemical impedance spectroscopy (EIS). As well as the metal surface morphology was analyzed by Atomic Force Microscopy (AFM). In addition, the chemical characterization of green inhibitor is carried out by Fourier Transform Infrared (FTIR). EIS revealed that the Ficus carica extract formed a thin protective film on the metal surface and by using of 300 ​ppm of extract of Ficus carica allow reaches (92.7%) of corrosion inhibition efficiency (CIE). The PDP curves revealed that the Ficus carica extract act as a mixed-type inhibitor. It was demonstrated that %IE enhanced with rising the Ficus carica extract doses also increased with arises in temperature (95.7%). Kinetic parameters and thermodynamic adsorption of the system have also been measured and studied. The data obtained revealed that the adsorption of Ficus carica on metal surface followed the Temkin isotherm and according to the activation energy (Ea1) the Ficus carica extract acts by chemisorption process. The results from unlike measurements were in a well accord.     

The study of self-assembled films of triazole on iron electrodes using electrochemical methods,XPS, SEM and molecular simulation

3-Alkyl-4-amino-5-mercapto-1,2,4-triazole (AAMT) has been evaluated as corrosion inhibition for iron in 0.1 M H₂SO₄ when the films of AAMT were self-assembled on the surface of iron. The films of AAMT inhibitor were characterized by electrochemical impedance spectroscopy, electrochemical polarization curves Results revealed that AAMT performed excellently as a corrosion inhibitor for iron in H₂SO₄ solution. Surface analysis was carried out using X-ray photoelectron spectroscopy and scanning electron microscope. The mechanism of adsorption was discussed using molecular simulation.     

Effect of hyamine on electrochemical behaviour of brass alloy in HNO3 solution

The electrochemical behaviours of a brass alloy in 0.1 M nitric acid, including the hyamine inhibitor with concentrations between 2.5 × 10^?4 M and 1.0 × 10^?5 M, were studied. For this purpose, potentiodynamic polarisation, electrochemical impedance spectroscopy (EIS), linear polarisation resistance (LPR) techniques, and flame atomic absorption spectroscopy (FAAS) were utilised. The inhibitor molecules adsorbed on the brass surface were calculated to be in good agreement with the Langmuir adsorption isotherm and the standard free enthalpy of adsorption (??G _ads ^° ). Hyamine effectively improved the corrosion inhibition of brass and acted as a mixed-type inhibitor on alloy surfaces. The surface morphology of the alloy was also clarified by optical microscopic and SEM techniques. A theoretical study of the corrosion inhibition efficiency of hyamine molecule was carried out using density functional theory (DFT) at the B3LYP/6-311G(d,p) basis set level.