Electrochemical corrosion behaviour of microcrystalline aluminium in acidic solutions

The electrochemical corrosion behaviour of microcrystalline pure aluminium coating, fabricated by a magnetron sputtering technique, has been investigated in both 0.5 mol/l NaCl and 0.5 mol/l Na₂SO₄ acidic (pH = 2) aqueous solutions. The corrosion resistance of the microcrystalline Al coating has deteriorated more compared with that of the cast pure Al in Na₂SO₄ acidic solution. However, its oxide film has a higher pitting resistance in the NaCl acidic solution. Chloride ions play a big role in the formation of the oxide film on the microcrystalline Al coating. The higher pitting resistance was attributed to the more acidic isoelectric point which the oxide film achieved.     

Corrosion inhibition of aluminium in acidic and alkaline media by Sansevieria trifasciata extract

The inhibitive action of leaf extracts of Sansevieria trifasciata on aluminium corrosion in 2 M HCl and 2 M KOH solutions was studied using the gasometric technique. The results indicate that the extract functioned as a good inhibitor in both environments and inhibition efficiency increased with concentration. Synergistic effects increased the inhibition efficiency in the presence of halide additives. Temperature studies revealed a decrease in efficiency with rise in temperature and corrosion activation energies increased in the presence of the extract. A mechanism of physical adsorption is proposed for the inhibition behaviour. The adsorption characteristics of the inhibitor were approximated by Freundlich isotherm.     

砷黄铁矿在酸性体系下的电化学氧化

在酸性体系下研究砷黄铁矿的电化学氧化。结果表明:砷黄铁矿首先被氧化为As2S2,覆盖于电极表面,使电极表面发生钝化;随着电位的继续升高,As2S2被氧化生成亚砷酸,随后亚砷酸被氧化为砷酸,亚铁离子被氧化成铁离子。不同pH和温度下的腐蚀动力学研究表明,随着pH值的增大,体系的腐蚀电位正移,腐蚀电流密度减小;随着温度的升高,砷黄铁矿的腐蚀电位负移,腐蚀电流密度增大。说明在研究的pH及温度范围内,降低体系的pH或提高温度都有利于砷黄铁矿的氧化。交流阻抗研究结果表明,不同电位下电极表面发生的电化学反应机理不同,测定结果与线性扫描的研究结果相吻合。     

Electrochemical behaviour of microcrystalline aluminium in neutral fluoride containing solutions

The electrochemical behaviour of microcrystalline pure aluminium coating (mc-Al), fabricated by a magnetron sputtering technique, has been investigated in NaF as well as NaF + NaCl aqueous solutions. Results indicate that the anodic polarization characteristic changes with NaF concentration. F⁻ anions promote the formation of a passive film, whose semiconducting properties were investigated. When the F⁻ concentration is high ([F⁻] ? 0.03 mol/L) the passive film is mainly composed of aluminium fluoride, which is an n-type semiconductor on mc-Al and a p-type semiconductor on polycrystalline Al (pc-Al). In NaF + NaCl aqueous solutions, Cl⁻ and F⁻ ions compete in affecting the type of semiconducting passive films formed on mc-Al.     

从盐酸介质中加压氢还原铱的动力学研究

考察了搅拌强度、铱的初始浓度、氢分压、盐酸浓度、氯离子浓度、温度及晶种对氢还原铱反应速率的影响.实验表明,氢还原过程是多阶段多步骤联合控制的复杂多相反应,已还原的铱起着自催化作用.同时根据动力学实验结果探讨了反应机理,指出前人未用氢将铱配离子还原为金属乃系其实验温度过低所致.     

元宝枫叶提取物在硫酸中对钢的缓蚀作用

采用失重法、动电位极化曲线和电化学阻抗谱(EIS)研究了元宝枫叶提取物在0.5 mol/L H28O4溶液中对冷轧钢腐蚀的影响.结果表明:元宝枫叶提取物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;元宝枫提取物为混合抑制型缓蚀剂;EIS谱在高频区呈容抗弧,在低频区出现感抗弧,电荷转移电阻随...     

Novel thiophene symmetrical Schiff base compounds as corrosion inhibitor for mild steel in acidic media

The inhibiting effect of two Schiff bases on the corrosion of the mild steel (MS) in 1 M HCl has been studied by electrochemical impedance spectroscopy (EIS) and Tafel polarisation measurements. The Schiff bases, 4,4′-bis(3-carboxaldehyde thiophene) diphenyl diimino ether (L₁) and 4,4′-bis(3-carboxaldehyde thiophene) diphenyl diimino ethane (L₂), were synthesized using 3-carboxaldehydethiophene and its corresponding amine. Polarisation curves reveal that both compounds are mixed type (cathodic/anodic) inhibitors and inhibition efficiency (% IE) increases with increasing concentration of compounds. It is suggested that their effects depend on their concentrations and the molecular structures. Adsorption of compounds on mild steel surface is spontaneous and obeys Langmuir’s isotherm.     

Inhibition of mild steel corrosion in CO2 and H2S-saturated acidic media by a new polyurea-based material

Oil well acidizing is a common practice used to boost oil well productivity in the industry. This practice, however, exposes the mild steel components of the wells to extremely harsh corrosive environments. Under such conditions, highly efficient inhibitors are used to minimize corrosion attack. In the present study, corrosion inhibition of mild steel in simulated acidic medium saturated with CO₂ and H₂S gases by a newly synthesized polyurea-based material (PUCorr-1) was investigated. Electrochemical studies supported with quantum chemical density-functional theory calculations and surface characterization revealed that PUCorr-1 adsorbs onto mild steel through a chemisorption mechanism yielding a stable protective film. The polyurea exhibited an excellent efficiency of 99.9% at a temperature of 50°C and a low concentration of 100 ppm, yielding a corrosion current density of 0.3 µA/cm². In the presence of CO₂ and H₂S gases, PuCorr-1 exhibited a remarkable performance (>93% efficiency) making it a potential corrosion inhibitor in industrial processes that involve the use of acid solutions in the presence of CO₂ and H₂S gases.     

The behavior of aluminum in alkaline media

Polarization and impedance measurements were performed on aluminum in 0.1, l and 3 mol/l NaOH. The frequency range studied was 1×10⁻²–1×10⁴ Hz in the potential range −2 to −1 V vs. SCE. In polarization experiments the potential was extended up to 0 V vs. SCE. The behavior of the system was characterized by a high frequency capacitive loop related to the charge transfer due to dissolution of the metal, an inductive loop at medium frequency which we have attributed to surface roughening and a second capacitive loop obtained at low frequency which has been ascribed to the adjustment of the surface film to the change in potential resulting in higher charge transfer resistance.     

Repassivation and pitting of freshly generated aluminium surfaces in acidic nitrate solution

The behaviour of freshly generated surfaces of aluminium in acidic nitrate solution is presented. The surfaces were generated by guillotining in situ, both in open circuit and under galvanostatically applied anodic current density. In the absence of externally applied polarisation, the open-circuit potential shows a logarithmic increase with time of polarisation. The form of the open-circuit potential transient is interpreted as high-field growth kinetics of the passivating oxide film, accompanied by the cathodic reduction of water or of nitrate anions under Tafel’s Law: both reduction reactions are detected in different regimes. The gradient, ∂E/∂ log t, of the open-circuit potential with time, is the Tafel slope of the cathodic reaction. At longer times, the formation of pores in the growing surface oxide is detected as a peak followed by a shallow decay in the potential transient. When the metal is galvanostatically anodically polarised, the potential of the freshly generated metal surface rises more rapidly and rises further, the extent of both depending on the applied current density. At low applied current densities, the oxide forms pores detected as a maximum in the potential, provided the potential remains lower than the pitting potential. At sufficiently high applied current density, the potential rises until the pitting potential is reached. Thence the potential falls a little followed by a constant mean value. The experiments show the pitting potential of aluminium in nitrate solution to be 1.6 V(SCE), dependent on the nitrate concentration.     

Electrochemical study of corrosion in aluminium cans in contact with soft drinks

This work evaluates the corrosion resistance of the inner surface of the aluminium cans in guarana, cola flavoured and tonic water soft drinks using electrochemical impedance spectroscopy (EIS) measurements. The less aggressive electrolyte was tonic water. One time constant was identified for the aluminium can in contact with guarana and tonic water. In the most aggressive medium of cola flavoured soft drinks, two time constants were identified and a charge transfer resistance was obtained associated to a corrosion of aluminium in contact with the electrolyte.     

Electrochemical behavior of copper-nickel alloys in acidic chloride solutions

The electrochemical behavior of Cu-Ni alloys in acidic chloride medium was investigated. Commercial Cu-Ni alloys were investigated using potentiodynamic techniques, complemented by electrochemical impedance spectroscopy. The influence of alloy composition, chloride ion concentration and immersion time on the electrochemical response of the alloys was analyzed. Results of present investigations with pure metals (Cu and Ni) are also considered in this paper for the sake of comparison. Potentiodynamic measurements reveal that the increase in nickel content decreases the corrosion rate of the alloy and when the nickel content exceeds 30%, an increase in the corrosion rate was recorded. Also, the corrosion current density increases with increasing the concentration of chloride ions up to 0.6 M.The experimental impedance data were fitted to an equivalent circuit model representing the electrode/electrolyte interface. The relevance of the proposed model to the corrosion/passivation phenomena occurring at the electrode/solution interface was discussed.     

Electrochemical behavior of titanium‐tantalum alloys in sulfuric acid solutions

Titanium exhibits a good corrosion resistance in oxidizing acids and neutral media but it is severely attacked in reducing acids. On the contrary, tantalum presents an excellent resistance in both oxidizing and reducing acids, but its high cost limits its use to very aggressive conditions. The titanium‐tantalum alloys are promising materials for use in reducing acids, due to their lower cost and density when compared to tantalum, and their higher corrosion resistance when compared to titanium. Titanium‐20, 40, 60 and 80 wt% tantalum alloys were prepared by arc‐melting and their microstructures were characterized by scanning electron microscopy and X‐ray diffractometry. Their electrochemical behaviors were studied in 20 to 80 wt% sulfuric acid solutions at room temperature, using open‐circuit potential measurements, potentiodynamic polarization and electrochemical impedance spectroscopy. Different behaviors were observed depending on the tantalum content and acid concentration. A clear tendency of increase in corrosion resistance with the increase of tantalum content is observed, especially in 80 wt% sulfuric acid solutions.     

The activation of aluminium by mercury ions in non-aggressive media

The presence of Hg at concentration less than 300 ppm in Al base alloys causes their passivation breakdown. On alloys used as sacrificial anodes, it causes a major lowering (>0.3 V) in their operational potential in chloride media. Mercury as trace constituent in the natural gas stream causes severe damage to cryogenic heat exchangers. The present paper presents evidences of the mechanism by which mercury produces its pronounced effect in aqueous non-aggressive media. The work was carried out using pure (99.99%) aluminium and mercury (II) acetate solutions of different concentrations and pH. Open circuit potential–time responses were obtained. The surface effects were followed by means of scanning microscopy and EDAX/X-Ray analysis. The results demonstrate that immediately after immersion, the initial air-formed oxide film underwent a dynamic crack–healing process at flaws in the film, possible associated to grain boundaries. The subsequent healing process, if any, depends on the media composition. Thus, in this special case, Hg²⁺ ions can be directly reduced on the bare aluminium, reaching a true metallic contact, and initiating surface diffusion. This enables the formation of an amalgam. Aluminium atoms diffuse through the liquid mercury and undergo oxidation at the amalgam/electrolyte interface. This process is responsible for the oxide detachment (by undermining) and the attack morphology (i.e., wide cavities).The presence of aggressive anions is not needed to initiate activation.     

常温酸性条件下黄铜矿的电化学行为

在温度为25℃及pH=2的条件下，通过循环伏安法和恒电位I-t曲线研究了黄铜矿特殊的电化学分解行为。通过循环伏安曲线发现：电位在400-800mV（vs SHE）范围内，黄铜矿电极表面的阳极氧化反应电流很小0主要是由于生成的中间产物很难被进一步氧化分解，从而产生了钝化；当电位小于-400mV（vs SHE）时，黄铜矿阴极还原反应电流较大，晶格中的Fe^3＋能较快地溶解出来，产生的中间产物（铜的硫化物）在氧化电位下发生较强的阳极氧化分解反应，但是随后反应进一步被钝化。黄铜矿的阴极还原反应较强烈，且对黄铜矿氧化浸出具有重要意义。此外，恒电位I-t曲线也证实了以上结论。     

长春花提取物对Q235碳钢在酸性溶液中的缓蚀作用

目的 开发一种绿色缓蚀剂,并研究它对碳钢在酸性溶液中的缓蚀作用及机理。方法 用体积分数为70%的乙醇水溶液回流获得长春花提取物(CR-E),通过失重实验、电化学综合实验、火焰原子吸收分光光度法(FAAS)、傅里叶变换红外光谱(FTIR)和扫描电子显微镜(SEM)等分析CR-E对Q235碳钢在0.5 mol/L H₂SO₄溶液中的缓蚀性能和机理。结果 CR-E对Q235碳钢在H₂SO₄溶液中的腐蚀具有良好的缓蚀效果,缓蚀效率随着CR-E浓度的增加而增大,在CR-E的质量浓度为1000mg/L时,缓蚀效率达到89.84%。添加CR-E后可迅速抑制腐蚀,并持续发挥缓蚀作用,在浸泡48 h后Q235碳钢的缓蚀效率仍可达89.99%;电化学综合实验结果表明,CR-E是一种有效的混合抑制型缓蚀剂,腐蚀反应的电荷转移电阻随着CR-E浓度的增加而增大,腐蚀电流密度则随之减小;通过FAAS证实阳极铁的溶解被抑制,通过FTIR证实CR-E分子可以有效吸附在Q235碳钢表面,通过SEM证实Q235碳钢表面受到了CR-E的...     

Control of zinc corrosion in acidic media: Green fenugreek inhibitor

Fenugreek seeds extract was examined as a green corrosion inhibitor for Zn in 2.0 mol/L H₂SO₄ and 2.0 mol/L HCl solutions by mass loss and electrochemical measurements. Scanning electron microscope (SEM) images show that the surface damage is decreased in the presence of the inhibitor. X-rays photoelectron spectroscopy (XPS) analysis was performed to identify the corrosion product, ZnO, and to prove the inhibitor adsorption mechanism. The maximum inhibition efficiency values are 90.7% after 1 h and 66.6% after 0.5 h by 200 mL/L of fenugreek extract in H₂SO₄ and HCl solutions, respectively. Addition of I⁻ ion greatly improves the inhibition efficiency of fenugreek seeds extract for Zn corrosion in HCl due to the synergistic effect. Potentiodynamic polarization and EIS measurements prove the inhibition ability of fenugreek for Zn corrosion in HCl as indicated by the decreased corrosion current density and increased charge transfer resistance values in the presence of fenugreek.     

New imidazole-based dimers as potential inhibitors for mild steel corrosion in acidic media: Electrochemical and DFT evaluation

We report the synthesis and corrosion inhibition performance of two imidazole-based materials, 1,1′-(4-methyl-1,3-phenylene)bis(3-(3-(1H-imidazol-1-yl)propyl)urea) (PIP) and 1,1′-(hexane-1,6-diyl)bis(3-(3-(1 H-imidazol-1-yl)propyl)urea) (HIP) dimers, in 1.0 M HCl. Electrochemical assessments indicated that the synthesized dimers facilitated the formation of a protective layer at the metal-electrolyte interface and, as a result, blocked the active corrosion sites. At a concentration of 100 ppm, PIP behaved as a potential mixed-type anticorrosive material with an overall efficiency of 99%. Density functional theory calculations showed that the aromaticity existing in the PIP backbone plays a major role in facilitating the corrosion-inhibition role.     

Investigation on the corrosion inhibitive effect of 2H-pyrazole-triazole derivatives in acidic solution

Four research methods, such as weight loss test, electrochemical techniques, adsorption isotherm, and quantum chemical calculation, were employed in this paper to study the inhibition efficiency (IE) and inhibition mechanism of three 2H-pyrazole-triazole derivatives, BHOT, FHOT, and CHOT in 1 M HCl solution for mild steel. Using the electrochemical technique, three inhibitors were proved to show a mixed-type character for mild steel by suppressing both anodic and cathodic reactions on the steel surface. The adsorption models of three compounds were established at different temperatures according to their adsorption isotherms. The results of the quantum chemical calculation method indicated that the adsorption sites of 2H-pyrazole-triazole derivatives were strongly centralized on benzene ring, triazole ring, or other substituents. All the results showed that the three derivatives were excellent inhibitors in 1 M HCl solution for mild steel.     

Spectrophotometric study of corrosion inhibition of aluminium in orthophosphoric acid aqueous solutions by using sodium molybdate

ABSTRACT

The kinetics of the corrosion of aluminium in the orthophosphoric acid aqueous solution was investigated spectrophotometrically and gravimetrically. Sodium molybdate was applied as the inhibitor of the corrosion process. The analysis of the results obtained indicated that there are at least two species that might be useful for the inhibition of the corrosion. These are the products from the reduction of molybdophosphoric acid with aluminium. The mechanism of the inhibition of the corrosion depends on the initial concentration of sodium molybdate.