Studies of protection of iron corrosion by rosin imidazoline self‐assembled monolayers

A type of rosin imidazoline (IM) has been synthesized using rosin acid and diethylenetriamine (DETA) as raw materials. The monolayers of IM were assembled on the surface of iron. The monolayers of the IM inhibitor were characterized by electrochemical impedance spectroscopy (EIS), electrochemical polarization curves and double‐layer capacitance. Surface analysis was carried out to establish the mechanism of corrosion inhibition of iron by X‐ray photoelectron spectroscopy (XPS) and scanning electron microscopy. The IM inhibitor showed good inhibition efficiency for iron in 0.1 M H₂SO₄. The inhibition mechanism of IM inhibitor was interpreted using molecular simulation. Copyright © 2006 John Wiley & Sons, Ltd.     

EIS investigation of a Ce-based posttreatment step on the corrosion behaviour of Alclad AA2024 anodized in TSA

In the aircraft industry, anodizing and posttreatment steps use Cr (VI) compounds, which, despite offering good corrosion resistance and self-healing properties, are highly toxic and carcinogenic. Ce compounds are recognized as efficient corrosion inhibitors for Al alloys, and several works report self-healing ability for these chemicals. In this investigation, the corrosion resistance of Alclad AA2024-T3 alloy anodized in tartaric-sulphuric acid (TSA) bath and posttreated in a solution comprising cerium nitrate without and with hydrogen peroxide was evaluated. The purpose is to investigate the potentiality of using hydrothermal treatment in Ce nitrate solution as candidate to replace Cr (VI) posttreatment. The aim is to provide a posttreatment step which, while improving the corrosion resistance, does not plug the mouths of the pores maintaining the adhesion properties of the porous anodic layer. Microstructural characterization was carried out by SEM-EDS whereas corrosion resistance was evaluated by EIS. The surface analysis showed that the posttreatments, all performed at 50°C, kept the open structure of the pores. EIS analysis showed that the posttreatments performed in the H₂O₂ solution for short immersion times were the most effective in improving the corrosion resistance of the samples, whereas electrical equivalent circuit (EEC) fitting of the data indicated sealing of the porous layer during the immersion of the different samples in the test solution. SEM-EDS analysis of the samples posttreated in the H₂O₂ containing solution, prior and after the corrosion test, showed the presence of Ce oxy-hydroxide randomly deposited on the sample surface, indicating that Ce could be incorporated/stored in the anodic layer.     

Electrochemical corrosion behavior of nanocrystalline zinc coatings in 3.5% NaCl solutions

The corrosion behavior of electrodeposited nanocrystalline (NC) zinc coatings with an average grain size of 43 nm was investigated in 3.5% NaCl solutions in comparison with conventional polycrystalline (PC) zinc coatings by using electrochemical measurement and surface analysis techniques. Both polarization curve and electrochemical impedance spectroscopy (EIS) results indicate that NC and PC coatings are in active state at the corrosion potentials, and NC coatings have much higher corrosion resistance than PC ones. The corrosion products on both coating surfaces are mainly composed of ZnO and Zn₅(OH)₈Cl₂·H₂O, but the corrosion products can form a relatively more protective layer on NC coating surfaces than on PC coatings. The EIS characteristics and corrosion processes of PC and NC zinc coatings during 330 h of immersion were discussed in detail.     

温度对铅阳极膜电化学性能的影响

利用线性电位扫描法、交流伏安法、电化学阻抗谱(EIS)及Mott-Schottky方程, 研究了温度对纯铅在4.5 mol/L H₂SO₄溶液中形成的阳极腐蚀膜电性能的影响. 结果表明: 温度对膜电化学性能具有显著的影响, 随着温度的升高, 膜的电阻增加, 孔隙率增加, 传递电阻减小. EIS结果表明膜的生长遵循固相机理, Mott-Schottky曲线显示腐蚀膜呈现n型半导体特性, 随着溶液温度升高, 膜内的施主密度减小.     

Corrosion inhibition of iron in hydrochloric acid using pyrazole

The corrosion and corrosion inhibition of iron in HCl solutions in the absence and presence of pyrazole (PA) were investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Changes in impedance parameters (R_ct and C_dl) were indicative of the adsorption of PA on the iron surface. The adsorption of PA is found to obey Langmuir adsorption isotherm. The study suggests that this compound is an anodic inhibitor.     

Electrochemical investigation of corrosion and corrosion inhibition of iron in hydrochloric acid solutions

The inhibition effect of 1-methyl pyrazole (MPA) on the acidic corrosion of iron in 1.0 M HCl was studied at different concentrations (10^?3–10^?2 M) by potentiodynamic polarization and electrochemical impedance spectroscopy, and EIS measurements. It is found from the polarization studies that methyl pyrazole (MPA) behaves mainly as anodic inhibitor in HCl. Values of polarization resistance (R_p) and double layer capacitance (C_dl) in the absence and presence of MPA in 1.0 M HCl are determined. The adsorption of MPA on iron surface from HCl is found to obey Temkin adsorption isotherm.     

Effect of pH,temperature, and H2O2 on the electrochemical oxidation behavior of iron in perchlorate solutions

The effects of pH, temperature, and H₂O₂ on the electrochemical oxidation behavior of iron were determined in perchlorate solutions. Iron exhibited four distinct oxidation behaviors in perchlorate solutions that had a pH of 3.0. First, the active dissolution potential with two current waves was observed in the range of ?0.7 to 0 V. Second, the range of stable passivation was observed between 0 and 0.3 V. Third, unstable passivation was observed in the range of 0.3 to 1.2 V. Finally, pitting corrosion was observed at a potential above 1.2 V. The increase in pH stabilized the passivation of iron, whereas the increase in temperature had a negative influence on both the passivation and pitting behaviors of iron. The presence of H₂O₂ at concentrations less than 1.45 mM had an adverse effect on the formation of the passive oxide layer. However, H₂O₂ at concentrations greater than 1.45 mM exerted a beneficial influence on the formation of stable iron oxide in the active dissolution region. In addition, H₂O₂ mitigated the pitting corrosion of iron regardless of the H₂O₂ concentration.     

Studying the fine microstructure of the passive film on nanocrystalline 304 stainless steel by EIS,XPS, and AFM

The fine microstructure of the passive films on nanocrystalline (NC) and coarse crystalline (CC) 304 stainless steels (SSs) in 0.5 M H₂SO₄ were investigated by electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The results indicate that the passive film on both CC and NC SSs exhibits a two-layer microstructure consisting of a compact inner layer and a porous outer layer. Some hydrated compounds (HC) were present in the porous outer layer of NC SS but not CC SS in 0.5 M H₂SO₄ solution. The pores in the outer layer of the NC SS were observed to be in the nanoscale by AFM. HC filling of the pores in the passive film on NC SS may occur due to capillary forces endowed by the nanosize pores. XPS analysis of the passive films on both CC and NC SSs, however, does not show such a composition difference which is attributed to dehydration occurring in the XPS vacuum chamber. Both the inner and outer layers of the NC SS were determined by EIS analysis to be more compact and protective than the corresponding films on CC SS as evidenced by the lower Q value, higher n, and much higher R value in the corresponding layer.     

Evolution of an iron passive film in a borate buffer solution (pH 8.4)

The evolution under open-circuit conditions of iron passive films formed at 0.8 V_SCE in a borate buffer solution at pH 8.4 was investigated with electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. The composition of the freshly formed passive film as determined by X-ray photoelectron spectroscopy (XPS) was found to be in agreement with a bilayer model, where the inner layer is composed mainly of iron oxide and the outer layer consists of a hydrated material. Results of XPS measurements also showed that the open-circuit breakdown of passive films was consistent with a reductive dissolution mechanism. When the iron electrode reached an intermediate stage in the open-circuit potential decay (approximately −0.3 V_SCE), the oxide film, containing both Fe(II) and Fe(III), was still protective. The impedance response in this stage exhibited a mixed control by charge transfer at the metal/film and film/solution interfaces and diffusion of point defects through the film. At the final stage of the open-circuit potential decay (approximately −0.7 V_SCE), the oxide film was very thin, and the ratio of Fe³⁺/Fe²⁺ and O²⁻/OH⁻ had decreased significantly. The impedance response also exhibited a mixed charge-transfer–diffusion control, but the diffusion process was related to transport of species in the electrolyte solution resulting from dissolution of the oxide film.     

Characterization of the passive films on electrodeposited Fe-Ni-Cr alloys in borate solution at pH 8.4

The corrosion properties of the passive layers formed on iron-nickel-chromium electrodeposits of Fe₂₉Ni₅₁Cr₂₀ were investigated in 0.3 M borate solution at a‘ pH of 8.4. On the basis of measurements by cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy, a low passive dissolution/corrosion rate was identified for the electrodeposited Fe-Ni-Cr alloys due to the nature of the established corrosion layer. The stability of this passive layer was further enhanced after corrosion under oxidizing conditions. Mössbauer spectroscopic measurements confirmed the existence of a thin passive layer on the amorphous electrodeposits.      

Synthesis of oxalate doped polyaniline and its corrosion protection performance

It is known that dopants present in polyaniline (PANI) play an important role in corrosion protection of mild steel since the dopant ions form a secondary layer with iron. Since oxalate ions form a stable iron oxalate layer on mild steel, a study has been made on the corrosion protection performance of steel by vinyl coating containing oxalate doped PANI in acid and neutral media. Electrochemical impedance spectroscopy (EIS) studies have shown that the oxalate doped PANI is able to protect mild steel in sodium chloride solution since the impedance values are maintained at 10¹⁰ Ω cm² even after 100 days of exposure.     

模拟水中铜镍合金B10耐蚀性的光电化学研究

采用循环伏安、光电化学和电化学阻抗谱技术对模拟水中铜镍合金B10的腐蚀行为进行了研究.在电位从正往负向扫描中 B10表面膜显示p-型光响应,光响应来自电极表面的Cu2O层,但最大光电流比硼砂-硼酸中的要低。B10电极的耐蚀性能随着溶液中Cl-、SO42-和S2-浓度及pH的增加而降低。温度的升高会导致光电流由p-型转为n-型,耐蚀性能急剧下降。电化学阻抗谱测量结果与光电化学方法得到的结果相一致。     

Electrochemical study on corrosion process characteristics of the high-strength low-alloy steels in NaHSO3 solution

Electrochemical methods were used to study the characteristics of corrosion process for the high-strength low-alloy steel and carbon steel used as a huge oil storage tank in NaHSO₃ solution. The polarization curve results show that both steel samples take place in active solution, and the high-strength low-alloy (HSLA) steel has higher i _corr value than carbon steel, which is due to the small grain size that provides high density of active sites for preferential attack. The electrochemical impedance spectroscopy (EIS) results make known that the corrosion process presents two stages. In the first 136 h, one-time constant in EIS diagrams can be shown. Both steels have similar corrosion resistance due to the combination effects of the grain size and microstructure. After 240 h of immersion, a complete passive film forms on the specimen surface, and two-time constants can be shown in EIS diagram. The HSLA steel exhibited improved corrosion resistance when compared with the carbon steel, which is due to the effect of the shape Fe₃C in microstructure and the deposition of FeSO₄ on the electrode surface. The scanning electrode microscopy analyses show that both steels take place in homogenous corrosion, and the carbon steel shows higher surface roughness and many Fe₃C residues. XRD results show that both steels have similar phase constitutes of corrosion products.     

On the corrosion inhibition of iron in hydrochloric acid solutions,Part I: Electrochemical DC and AC studies

The inhibitive action of 4-methyl pyrazole (4MP) against the corrosion of iron (99.9999%) in solutions of hydrochloric acid has been studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). At inhibitor concentration range (10^?3–10^?2 M) in 1.0 M acid, the results showed that 4MP suppressed mainly the anodic processes of iron corrosion in 1.0 M HCl by adsorption on the iron surface according to Temkin adsorption isotherm. Both potentiodynamic and EIS measurements reveal that 4MP inhibits the iron corrosion in 1.0 M HCl and that the efficiency increases with increasing inhibitor concentration. Data obtained from EIS were analyzed to model the corrosion inhibition process through an equivalent circuit.     

The effect of the change in the microscopic structures of the iron on corrosion resistance and passivated properties

The passive film of iron showed n‐type semiconductor characteristic in borate buffer solution, and its donor concentration increased slightly after tensile strain in the present study. However, comparing with solution‐annealed sample, the anodic passive film formed on tensile‐strained one was highly protective. The more dislocations on tensile‐strained sample promoted the diffusion of iron and oxygen vacancy. Moreover, more donor density (mainly oxygen vacancies) promoted the diffusion of oxygen. They all facilitated tensile‐strained sample to form Fe₂O₃ and thicker passive film on the surface. More Fe₂O₃ and thicker passive film on the surface of tensile‐strained iron could improve corrosion resistance. Copyright © 2014 John Wiley & Sons, Ltd.     

Corrosion inhibition of steel in molar HCl by triphenyltin2–thiophene carboxylate

The effect of triphenyltin2–thiophene carboxylate (TTC) on the corrosion of steel in hydrochloric acid medium was studied using gravimetric, electrochemical polarisation and electrochemical impedance spectroscopy (EIS) measurements. The percentage inhibition efficiency was found to increase with increasing concentration of inhibitor to reach 97% at 10^?3 M. Polarisation study shows that TTC is an efficient inhibitor and acts as a mixed-type inhibitor. EIS results indicate the increase of resistance transfer (R_T) and the decrease of double layer capacitance (C_dl) with TTC concentration. Triphenyltin2–thiophene carboxylate molecules lead to the formation of a protective layer on the surface of steel. The inhibitor is adsorbed on the steel surface according to Langmuir isotherm.     

Adsorption and corrosion inhibition behavior of polyethylene glycol on α-brass alloy in nitric acid solution

The corrosion performance of α-brass in 1 M HNO₃ and in the presence of polyethylene glycol (PEG) has been investigated using AC impedance spectra (EIS), potentiodynamic polarization (PP), electrochemical frequency modulation (EFM), and mass reduction (MR) techniques. The outcome data of EIS showed a rise in the resistance charge transfer (R_ct) and a decrease in the capacitance double layer (C_dl). Protection efficiency (IE) of PEG has been obtained by varying the dose of the PEG and temperature. PEG adsorbed on α-brass in acidic solution follows isotherm Langmuir. The polarization curves displayed that PEG acts as a mixed-kind inhibitor. The parameters obtained from thermodynamic activation of corrosion α-brass in 1 M HNO₃ were obtained and debated. The results obtained from all tests were in excellent agreement.     

Composite SiO2—Iron Oxide Materials for Magnetically Intensified Adsorption

Composite SiO₂—iron oxide materials were prepared by three experimental procedures. In the first case, the iron oxides were precipitated during a sol-gel process. In the second case, a SiO₂ matrix was initially obtained, and the iron oxides were formed by thermal treatment after impregnation of a soluble Fe²⁺ salt in the previously processed matrix. In the third method, ferrite powders, prepared by wet chemical method, were embedded into a SiO₂ based sol-gel matrix. Materials with convenient porosity and nano-sized iron oxide content could be prepared using the mentioned methods. The prepared composite has been tested for arsenic(V) removal.     

Adsorption,Thermodynamic, and Experimental Studies of Corrosion Inhibitor of Tin in 0.2 M Maleic Acid by Hydrogen Phosphate Ions (HPO42−)

The inhibition efficiency of H₂PO₄²⁻ ions against tin corrosion in 0.2 M maleic acid is studied using electrochemical methods, surface analytical methods, and thermodynamic analysis. The potentiodynamic polarization plots showed the presence of an active/passive transition state of the tin electrode. The EIS measurements confirmed that the inhibition efficiency of H₂PO₄²⁻ increased by increasing the concentration (η=81 % at C_inh=2.10⁻² M) and decreased by rising the temperature. The polarization tests demonstrated that the inhibitor performs as a cathodic-type. The adsorption of the inhibitor was spontaneous and followed the Langmuir adsorption isotherm. A model of the inhibition mechanism was suggested.     

Synthesis,X-ray structure and theoretical study of benzazole thioether and its zinc complex as corrosion inhibitors for steel in acidic medium

A ligand, 2-((benzo[d]thiazol-2-ylthio)methyl)-1H-benzo[d]imidazole, and its zinc complex have been synthesized. The structure of these compounds have been determined by spectroscopic techniques and single crystal X-ray diffraction. The corrosion inhibition study of these compounds for steel in 0.5 M H₂SO₄ medium has also been investigated using potentiodynamic polarization and EIS techniques. The quantum calculations were applied to investigate the relationship between the electronic properties and the corrosion inhibition efficiency of the two benzazoles derivatives. Surface analysis (XRF) indicated that the rust layer formed on the Cu-containing steels was enriched with Cu compounds. Polarization curves revealed that both inhibitors acted as a mixed-type inhibitor.