Electrochemical behaviour of aluminium in the presence of EDTA-containing chloride solutions

The electrochemical behaviour of pure aluminium in an EDTA-containing chloride solution was investigated using potentiodynamic and potentiostatic electrochemical techniques and electrochemical impedance spectroscopy. A pronounced EDTA-induced anodic dissolution was observed in alkaline solutions, but the presence of EDTA in solution had little activating effect on the passivation properties at pH values close to 4.0. This was attributed to the relative stability of the Al(EDTA)^– complex formed at the different pH values. This EDTA-induced activation had no deleterious effect on pitting attack, in fact, higher breakdown potentials were observed in the presence of EDTA. This was attributed to the buffering action of EDTA, which inhibited the attainment of a critical pit solution composition. But, in the presence of molybdate, EDTA had no observable effect on pitting attack. The impedance spectra recorded in the presence of EDTA showed evidence for the adsorption of EDTA species during the dissolution process, which in turn, form a large capacitive network, with capacitance values of the order of 3 mF cm^–2 in the low frequency region.     

Influence of alloying additives on corrosion and hydrogen permeation through commercial aluminium in alkaline solution

The influence of alloying additives on the extent of corrosion and hydrogen permeation through aluminium of different grades such as 2S, 3S, 26S and 57S, in 0.01 M NaOH has been investigated using weight loss measurements and electropermeation. It is found that the extent of self corrosion and hydrogen permeated through different grades of commercial aluminium follow the order: 3S > 2S > 26S > 57S. The influence of incorporating zinc and indium either alone or in combination on self corrosion and permeation current has also been studied. It is found that ternary alloys of both 26S and 57S containing zinc and indium give considerably lesser values of self corrosion rate and permeation current.     

Electrochemical behaviour of cobalt in aqueous solutions of different pH

A systematic study of the corrosion and passivation behaviour of cobalt in aqueous solutions of different pH was carried out. Open circuit potential measurements, polarization experiments and electrochemical spectroscopic (EIS) investigations were employed. The experimental results show that the metal surface is always covered by a native passive film which consists of CoO. The formation of the oxide film obeys a two-electron charge transfer process. The dissolution of the barrier film is controlled by the pH of the solution. In neutral and basic solutions the barrier film is stable. In these media a barrier film thickening with the formation of secondary layer is considered. In acidic solutions, the passive film is unstable and dissolves via a pure chemical process. The mechanism of the corrosion and passivation processes taking place at the electrode/electrolyte interface in the different solutions is discussed. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to confirm the electrochemical measurements and the suggested mechanisms.     

Influence of power ultrasound on the corrosion of aluminium and high speed steel

The influence of power ultrasound on the corrosion of aluminium and high speed steel in chloride medium has been investigated. Open circuit potential, polarization curves and electrochemical impedance spectroscopy were employed to study the corrosion process before, during and after ultrasonic irradiation as well as scanning electron microscopy of the corroded surfaces. Cavitation led to formation of pits, erosion and increased mass transport. The effect of ultrasound power, chloride concentration, horn tip–metal distance and of tip diameter were assessed. The principal effect of ultrasound on aluminium is destruction of the oxide film and on high speed steel removal of corrosion products and increased solution mass transport; the influence of ultrasound is greatest at low chloride concentrations. For both metals it was shown that for chloride ion concentrations up to 0.1 M the influence of ultrasound power is most evident, followed by the distance between probe tip and metal, then [Cl^–] and lastly the size of the probe tip. The potentialities of using ultrasound as a rapid diagnostic test of corrosion resistance are indicated.     

铝合金在不同电解液体系中微弧氧化过程的研究

为比较不同电解液体系下各种工艺参数对铝合金微弧氧化膜性能及耐腐蚀能力的影响,通过微弧氧化法在NaOH、Na2S iO3、NaH2PO4、Na2CO3四种电解液体系分别制备了铝合金氧化膜。通过点滴腐蚀实验比较了四种电解液体系所得氧化膜的耐腐蚀能力,利用扫描电子显微镜(SEM)观察分析了氧化膜的表面形貌。实验表明,在这四种电解液体系中起弧电压均随浓度的降低及电极间距离的增加而逐步升高,而膜厚与氧化电压、时间的增加成正比,但成膜速率随时间的延长而逐渐减缓,在各体系中这些变化的具体情况仍有所区别。其中以NaOH体系所得氧化膜的膜层较致密,微孔分布均匀,相同条件下耐蚀性能要优于其他三种电解液体系所制氧化膜。     

The inhibitive action of dimethyltin dichloride towards the corrosion of aluminium in hydrochloric acid and sodium hydroxide solutions

The dissolution of aluminium in hydrochloric acid and sodium hydroxide solutions in the presence of dimethyltin dichloride as corrosion inhibitor has been studied using hydrogen evolution and thermometric methods. The two methods gave consistent results. The higher inhibition efficiency of this compound in acidic than in alkaline media may be due to the less negative potential of aluminium in hydrochloric acid solution, favouring adsorption of the additive. The adsorption of this compound was found to obey Frumkin adsorption isotherm.     

Electrochemical and surface properties of aluminium in citric acid solutions

The electrochemical and surface properties of aluminium in 0.05 M citric acid solutions of pH 2–8 were studied by means of open circuit potential (OCP), potentiodynamic polarization and potentiostatic current–time transient measurements. The OCP reached a steady-state value very slowly, probably due to the slow rate of detachment of surface complexes into the solution. Aluminium exhibits passive behaviour in citric acid solutions of pH 4–8. Tafel slopes b _c were characteristic for hydrogen evolution on aluminium covered by an oxide film. The corrosion kinetic parameters E _corr, i _corr and b _a suggest that surface processes are involved in the dissolution kinetics, especially in the pH range 3–6. Current–time transient measurements confirm that, in citric acid solutions of pH 3–6, the dissolution is controlled by surface processes, that is, by the rate of detachment of surface complexes, while in solutions of pH 2, 7 and 8 dissolution is under mass-transport control. The addition of fluoride ions to citric acid changes the controlling steps of the dissolution process. Citrate and fluoride ions compete for adsorption sites at the oxide surface, and adsorption of these ions is a competitive and reversible adsorption.     

Influence of inorganic anions on electrochemical behaviour of pyrite

This work gives an investigation of pyrite behaviour during anodic oxidation in solutions of four inorganic acids: sulphuric, hydrochloric, phosphoric and perichloric acid. In wider range of concentrations, the influence of acids on following parameters was investigated: rate of establishment and corrosion potential value, Tafel's slope, corrosion current and electrodic reaction order. Based on potentiodynamic and chronoamperometric investigations, it was found out that pyrite oxidation is developed in three regions conditionally named active, passive and transpassive region. It was also found out that pyrite is intensively dissolved at potentials higher than 0.75 V versus SCE and that oxidation rate of pyrite is the highest in hydrochloric acid solutions (≥1 M HCl). By comparison of obtained results, it was concluded that there are no distinctive differences in pyrite behaviour during anodic oxidation in solutions of investigated acids.     

The corrosion and electrochemical behaviour of pure aluminium in alkaline methanol solutions

The corrosion and electrochemical behaviour of pure aluminium in alkaline methanol solutions has been investigated. The results of hydrogen collection experiments showed that aluminium has a lower corrosion rate in alkaline methanol solutions compared to water based solutions and that the corrosion rate increases with increasing water content of the solution. Polarization and galvanostatic discharge experiments showed that there is a wide potential window of electrochemical activity and a better discharge performance in the alkaline methanol solutions with a certain amount of water. Scanning electron microscopy (SEM) and energy dispersive analysis of X-ray (EDAX) showed that the passivation in the later stages of discharge in alkaline methanol solutions at relatively high current densities is due to the formation of a dense Al(OH)₃ layer on the surface of the anode.     

Effect of silicon alloying addition on the corrosion behaviour of aluminium in some aqueous media

The corrosion behaviour of three Al–Si alloys was studied after galvanostatic passivation in 0.1 M sodium tartrate, sulfate and borate solutions using EIS techniques. The degree of passivation depends on the anion type, the degree of polarization and the alloy composition. It was also found that increase in pH led to a decrease in polarization resistance R _p. The effect of formation voltage, V _f, on the growth and dissolution kinetics of the oxide grown on the alloys was studied. The polarization resistance value increases as V _f increases up to a certain value; above this the R _p value decreases. This critical V _f depends on the alloy composition and the test solution. The kinetics of oxide layer dissolution in the absence and presence of Cl^– ions was also studied. Increase in immersion time leads to a more severe attack by Cl^– ions as shown by the decrease in the value of R _p. At low Cl^– ion concentration the value of R _p is higher than that in chloride ion free sulfate solutions, because the rate of passive film repair is much higher than that of barrier layer dissolution. However, at high Cl^– ion concentration penetration of Cl^– through defects in the barrier layer leads to formation of an oxyhalide layer.     

Corrosion behaviour of some stainless steels in chlorinated Gulf seawater

The corrosion resistance of conventional and high alloy stainless steels (specifically 316L, 317L, 904L, duplex 2205, 3127hMO, 1925hMO, 254SMO, 654SMO and Remanit-4565) was determined electrochemically in chlorinated and unchlorinated Arabian Gulf Seawater at 25 and 50 °C. The stainless steels 316L and 317L were used as reference alloys. The electrochemical potentiodynamic cyclic polarization method was used to determine the passive film break down potential (E _b), protection potential (E _prot) and maximum current attained on scan reversal (I _max). It was found that at 25 °C in chlorinated and unchlorinated seawater and at 50 °C in unchlorinated seawater, stainless steels 316L and 317L have poor resistance to corrosion, Stainless steels 904L and duplex 2205 at 25 °C in chlorinated and unchlorinated seawater showed good resistance to corrosion but at 50 °C these steels failed to resist. The high alloy stainless steels such as 3127hMO, 1925hMO, 254SMO, 654SMO and Remanit-4565 showed better corrosion resistance under all the test conditions.     

重金属离子对5052铝合金耐蚀性能的影响

采用70℃脱氧人工海水模拟低温多效蒸馏海水淡化设备内部的特殊腐蚀环境,分析了不同含量的重金属Cu2+、Fe3+对5052铝合金腐蚀情况的影响。极化曲线结果表明,溶液中的微量重金属离子(10-9级)也会在铝合金表面沉积,使铝合金自腐蚀电位正移,但却不会破坏铝合金表面自然氧化膜,使点蚀电位保持不变。而腐蚀失重结果表明,随着溶液中氯离子对氧化膜的侵蚀、破坏,表面沉积金属与铝基体的耦合将加快铝合金腐蚀过程。     

Effect of curing on the corrosion protective properties of thin organosilane films on aluminium

Film properties and corrosion protection given by thin organosilane films (bis-1,2-(triethoxysilyl)ethane: BTSE) on aluminium were investigated as a function of curing. The thickness was determined using spectroscopic ellipsometry (SE). Impedance spectra, modelled by an electrical equivalent circuit, show three time constants. The variation of the elements in these three time constants as a function of the immersion time in a NaCl solution indicate the structure of the film after curing. It can be concluded that the barrier properties of the organosilane films are influenced more by the curing temperature than by the curing time.     

阴极保护法对化肥厂中铝材的有效保护

介绍了化肥厂中普遍存在的铝材设备腐蚀问题及相应的腐蚀机理，针对化学药剂难以完全抑制碳化水箱的局部腐蚀，详细介绍了阴极保护方法，并阐述了阴极保护的机理及阴极保护方案，还根据实际经验，重点介绍了具体实施过程中涉及到的问题，如设备尺寸及保护面积的计算、阴极与阳极的布置、设备的表面处理及涂层。为证明此方法的有效性，作者还专门从直观效果和试片检测两方面介绍采用阴极保护的应用效果。理论和实践证明，阴极保护法是保护化肥企业铝材设备的有效手段。     

Influence of electrolyte impurities on current efficiency in aluminium electrolysis cells

The influence of electrolyte impurity species on current efficiency with respect to aluminium (CE) was studied in a specially designed laboratory cell at 980C, with a graphite anode and a cathodic current density of 0.85Acm–2. The electrowinning was performed in a base melt of Na3AlF6 with a NaF/AlF3 molar ratio of 2.5 and with 4–6wt% Al2O3 and 5wt% CaF2. Impurity species, probably present in only one valence state in the electrolyte, Mg, Ba and B, had no measurable effect on CE for low impurity concentrations. Sn, added to the electrolyte as SnO2, also did not affect current efficiency, probably due to its low solubility. The results show a linear decrease in CE with increasing electrolyte concentration of the polyvalent impurity species from the elements, Fe, P, V, Si, Zn, Ti and Ga. The decrease was found to be within the range 0.1 to 0.7% in C E per0.01wt% of impurity cations present in the electrolyte, with phosphorus ions as the most detrimental. The effects of the individual impurity species on CE appear to be roughly additive for electrolytes containing more than one impurity species. The results obtained cannot be explained by a simple codeposition mechanism or a single reduction to a soluble species of a lower valency. The most likely mechanism explaining the observed decrease in CE for a large number of impurity species is cyclic redox reactions in the cathode and anode/CO2 interfacial boundary layers. Such a mechanism may also be the dominant one in commercial cells, since the impurity levels are of the same size as in the laboratory cell.     

Potentiodynamic behaviour of aluminium in propanedioic acid solutions

The electrochemical behaviour of aluminium in propanedioic acid solutions has been studied potentiodynamically, the sweep rates ranging from 1 to 100 mVs^–1 and the concentrations of the diacid being 0.05, 0.10, 0.50 and 1.00 m. The experimental work has been carried out with and without stirring of the electrolyte. The potentiodynamic curves are simple but reflect a complex behaviour. The potential of zero current in the anodic sweep is made considerably more anodic when the concentration of propanedioic acid increases, when the sweep rate decreases and when stirring is introduced. For a certain sweep rate the cathodic charge increases with both stirring and concentration of propanedioic acid. However, the anodic charge, although increasing with concentration, does not depend on stirring within experimental error (potential ranges between –2.00 and 0.400 and –2.00 and 2.90 V vs SCE). The experimental curves are explained by the increase of the quantity of reducible species near the electrode with diacid concentration, by the fact that the cathodic process is pore diffusion-controlled (H₂ evolution) and that near the potential of zero current the cathodic and anodic processes coexist (oxide formation and possible direct migration of the cation towards the solution).     

松香铝丙烯酸酯增粘树脂在水性复膜胶中的应用

报道松香铝丙烯酸酯的合成及其软化点、酸值,阐明其增粘机理,并与松香比较,讨论其对丙烯酸乳液型复膜胶聚合转化率、粘度、剥离强度的影响,得出松香铝丙烯酸酯在复膜胶中使用具有比松香更好的效果。     

Influence of aeration on the localized trenching on aluminium alloys

This paper aims to make the difference between alcalinisation and micro-galvanic corrosion in the mechanism of the corrosion of Al alloys. Using a pH microprobe, the pH changes inside a pure water droplet deposited on a thermal aged 2011 aluminium alloy were scanned. These pH variations, depending on the position inside the droplet, were related to the heterogeneous corrosion attacks of the aluminium surface quantified by AFM measurements. A modelling investigation is proposed to evaluate the distinct roles of alcalinisation, due to the oxygen reduction reaction (ORR), and the galvanic coupling between intermetallic particles and the surrounding matrix. It can be concluded that the former controls corrosion initiation and lateral extension whereas the latter governs the propagation kinetics.     

Passivity and passivity breakdown of 304 stainless steel in alkaline sodium sulphate solutions

The passivity and passivity breakdown of 304 stainless steel were investigated in 0.25 M Na₂SO₄solutions of pH 10. The effect of applied potential and the presence of Cl^– ions in the electrolyte were also studied. Different electrochemical methods such as open circuit potential measurements, polarization techniques and electrochemical impedance spectroscopy (EIS) were used. The results showed that the steel electrode passivates under open circuit conditions and also under potentiostatic control. The rate of passive film thickening under open circuit conditions follows a simple logarithmic law. Addition of Cl^– ion shifts the polarization curves in the active direction and above a critical chloride concentration, [Cl^– ] 0.15 M, pitting corrosion occurs and the pitting potential, E _pit, decreases linearly with the logarithm of [Cl^–]. The addition of sulphate ions to the chloride-containing solutions was found to inhibit the pitting process, and at [SO^2- ₄] 0.25 M, a complete immunity to pitting corrosion was recorded. The impedance measurements provided support for film thickening and film breakdown reactions. An equivalent circuit model which consists of a pure resistor, R , in series with a parallel combination of a pure resistor, R _p, and a constant phase element, Q, was proposed to describe the electrode/electrolyte interface. The passive film thickness was found to increase with applied potential up to a critical value of 0.3 V. At higher voltages, breakdown of the passive film occured.