Characterization of some aluminium alloys for application as anodes in alkaline batteries

This work deals with the evaluation and characterization of aluminium (99.61%) and some of its alloys namely, Al—Ga—In, Al—Zn, Al—In, Al—Mn and Al—Mg, as anodes in alkaline battery electrolyte. The self-corrosion rate, hydrogen evolution rate and electrochemical properties, such as open circuit potentials, polarization characteristics and anode efficiencies were examined in 4 M KOH solutions. Among the tested alloys, Al—Ga—In alloy is found to be the most promising since it exhibits high open circuit potential, minimum anodic polarization, good anode efficiency and minimum corrosion rate. On the other hand, Al—In and Al—Mn alloys show higher corrosion rate compared with the other alloys. It can be shown that, a stoichiometric correlation exists between the corrosion rate obtained by weight loss and the hydrogen evolution rate.     

Electrochemical Behaviour of Al, Al—In and Al–Ga–In Alloys in Chloride Solutions Containing Zinc Ions

The electrochemical behaviour of Al, Al—In and Al–Ga–In alloys in 0.6 m NaCl solutions with and without Zn²⁺ was investigated. The study was performed by means of open circuit potential, potentiodynamic polarization, potentiostatic current-time and electrochemical impedance spectroscopy measurements as well as by SEM-EDAX examination. It was found that the Al—In alloy exhibits the highest negative open circuit potential in 0.6 m NaCl and the corrosion resistance of the tested electrodes decreases in the following order: Al > Al–Ga–In > Al—In. The greater activity of the Al—In alloy was interpreted on the basis of the autocatalytic attack by indium. The potentiostatic current–time measurements in Zn²⁺ containing electrolyte at potentials above the pitting potential revealed that Zn²⁺ has an insignificant influence on the Al electrode, while it enhances the corrosion of the Al–Ga–In alloy and improves the attack morphology of the Al—In alloy. Furthermore, the impedance spectra recorded under open circuit conditions showed a decrease in the polarization resistance of Al—In and Al–Ga–In alloys in presence of Zn²⁺ indicating the activating effect of Zn²⁺ ions.     

Corrosion, passivation and breakdown of passivity of Al and Al-Cu alloys in gluconic acid solutions

The pitting corrosion of Al, and two Al-Cu alloys, namely (Al-2.5% Cu) and (Al-7.0% Cu) was investigated in gluconic acid (HG) solution through linear polarization and cyclic voltammetry techniques complemented with ex situ EDX and SEM examinations of the electrode surface. Inductively coupled plasma-atomic emission spectroscopy (ICP-AES) method of chemical analysis was used to study the effect of alloyed Cu on the rate of the uniform corrosion of Al in these solutions. Results obtained from ICP were compared with those obtained from polarization measurements. For the three Al samples, the anodic responses did not involve active/passive transition due to spontaneous passivation. Addition of HG induced pitting (confirmed from SEM) within the passive oxide film due to the aggressive attack of gluconate (G⁻) anions. Relationships between pitting potential (E_pit), HG concentration, temperature, pH and potential scan rate were established. Alloyed Cu was found to enhance uniform corrosion, while it suppressed pitting attack. Local acidification model is employed to explain passivity breakdown induced by pitting corrosion as a result of the aggressive attack of G⁻ anions.     

Characterization of corroding aluminium alloys with electrochemical noise and electrochemical impedance spectroscopy

Electrochemical impedance spectroscopy (EIS) and spontaneous voltage fluctuation measurements were made on three orthogonal faces of 7039-T64 and 2519 aluminium alloy specimens during 10 day exposure periods into aerated 3% NaCl solutions. The spontaneous voltage fluctuations generated by the specimens were analysed with two techniques designed to reveal the stochastic character of these signals and their fractal dimension to establish practical correlation between noise measurements and the degree of pitting of the corroding aluminium specimens. Attempts were made to correlate the results of these analyses with parameters measurable by microscopic examination of the specimens or calculated from EIS measurements. During this study it was found that the slope of the voltage fluctuations and the depression angle of EIS results were both good indicators of the pit density observable on the corroded aluminium specimens.     

Pitting corrosion studies on Al and Al-Zn alloys in SCN solutions

Pitting of Al and Al-6%Zn and Al-12%Zn alloys in KSCN solutions was studied by means of potentiodynamic anodic polarization, cyclic voltammetry, potentiostatic and impedance techniques. Measurements were conducted under different experimental conditions, complemented by ex situ scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDXA). The potentiodynamic anodic polarization curves do not exhibit active dissolution region due to spontaneous passivation. The passivity is due to the presence of thin film of Al₂O₃ on the anode surface (in case of Al) and the formation of ZnO on the Al₂O₃ matrix, in case of the two Al-Zn alloys (as evidenced from EDXA). The passive region is followed by pitting corrosion as a result of passivity breakdown by the aggressive attack of SCN⁻ anions. SEM images confirmed the existence of pits on the electrode surface. Alloyed Zn was found to enhance pitting attack. The pitting potential (E_pit) decreases with an increase in SCN⁻ concentration and temperature, but increases with increasing potential scan rate. The current/time transients show that the incubation time for passivity breakdown decreases with increasing applied positive potential, SCN⁻ concentration, and temperature. Impedance measurements showed that Nyquist plots are characterized by a depressed charge-transfer semicircle, the diameter of which is a function of SCN⁻ concentration, applied potential, solution temperature and sample composition.     

Zinc impregnation of the anodic oxidation layer of 1050 and 2024 aluminium alloys

The porous oxide layer obtained by phosphoric anodic oxidation (PAO) of 1050 and 2024T3 aluminium alloys is modified by impregnation with zinc under alternating voltage. The resulting current against applied voltage relationship shows that a threshold voltage is required to deposit the zinc. Beyond a low critical voltage, V _{c L}, zinc electrocrystallization starts near the barrier layer and grows with time through the porous oxide layer whatever the alloy used as substrate. For the 2024T3 alloy, beyond a high critical voltage V _{c H}, S.I.M.S. analysis shows that zinc is also present on top of the oxide layer. The distribution of zinc particles depends on the porous layer morphology: formation of zinc needles in a columnar form (1050 alloy) and dispersion of zinc particles in a disorganized structure (2024T3 alloy). The polarization curves obtained in a 3 wt % NaCl solution show a decrease in anodic and cathodic currents indicating a protective effect of zinc impregnation, confirmed by electrochemical impedance analysis.     

Uniform and pitting corrosion events induced by SCN anions on Al alloys surfaces and the effect of UV light

The influence of the alloying elements on the uniform and pitting corrosion processes of Al-6061, Al–4.5%Cu, Al–7.5%Cu, Al–6%Si and Al–12%Si alloys was studied in 0.50 M KSCN solution at 25 °C. Open-circuit potential, Tafel polarization, linear polarization resistance (LPR) and ICP-AES measurements were used to study the uniform corrosion process on the surfaces of the tested alloys. Cyclic polarization, potentiostatic current-time transients and impedance techniques were employed for pitting corrosion studies. Obtained results were compared with pure Al. Passivation kinetics of the tested Al samples were also studied as a function of applied potential, [SCN⁻] and sample composition by means of potentiostatic current transients. The induction time, after which the growth of stable pits occurs, decreased with increasing applied potential and [SCN⁻]. Regarding to uniform corrosion, alloyed Cu was found to enhance the corrosion rate, while alloyed Si suppressed it. Alloying elements of the tested samples diminished pitting attack to an extent depending on the percentage of the alloying element in the sample. Among the investigated materials, Al–Si alloys exhibited the highest corrosion resistance towards uniform and pitting corrosion processes in KSCN solutions. The passive and dissolution behaviour of Al was also studied under the conditions of continuous illumination (300–450 nm) based on cyclic polarization and potentiostatic techniques. The incident photons had a little influence on pit initiation and a marked effect on pit growth. These explained in terms of a photo-induced modification of the passive film formed on the anode surface, which render it more resistant to pitting. The effects of UV photons energy and period of illumination on the morphology of the pitted surfaces were also studied.     

葡甘聚糖/碳酸钙复合涂层对AA5052铝合金点蚀的抑制作用

通过自固化方式在AA5052铝合金表面制备新型绿色葡甘聚糖/碳酸钙复合涂层,采用SEM、FT-IR和XRD等手段对微观形貌、结构和组成进行表征,并研究其在NaCl溶液中对铝合金点蚀的抑制作用.结果表明:复合涂层厚度约50μm,具有树枝状微纳结构,可使铝合金电荷转移电阻提升5个数量级.复合涂层覆盖的铝合金耐腐蚀性能随氢氧...     

EIS testing of new aluminium sacrificial anodes

Aluminium alloys In/Hg free, suitable as sacrificial anodes for cathodic protection, have been developed. Short-term electrochemical tests were performed on these new alloys to obtain their electrochemical efficiency and to reveal any tendencies to passivation. Samples were galvanostatically held at different current densities, which changed every 24 h according to DNV RP 401. Electrochemical impedance spectroscopy (EIS), polarization curves and electrode potential against time measurements were employed to study the main features of the processes taking place at the alloy–solution interface.     

OC反应器腐蚀原因分析及解决对策

本文以理论分析为基础,对几种材料耐蚀性能进行了比较,论证了采用双相不锈钢制造OC反应器的零件能满足本设备耐腐蚀要求。     

Pyrrole-based silane primer for corrosion protection of commercial Al alloys. Part II. Corrosion performance in neutral NaCl solution

A chromate-free, direct-to-metal treatment using pyrrole-based silane (PySi) was developed for protection against corrosion of as-received commercial Al alloys, following the typical procedure for silane deposition. The protection performance of composite PPySi films, containing polysiloxane linkages and polypyrrole units, was evaluated in near neutral NaCl solution by simple corrosion tests such as single-cycle anodic polarization, corrosion potential monitoring and long-term immersion experiments. Control coatings of polymethylsiloxane (PMeSi) and electrochemically synthesized polypyrrole (Ppy) were also studied. The superior performance of PPySi with respect to PMeSi and Ppy was attributed to highly crosslinked, well-packed and adherent composite films of thickness of the order of microns, manifesting both barrier action and active protection. The use of pyrrole-based silane for corrosion protection of Al alloys constitutes a promising approach for effective replacement of chromium-based treatments in practical applications. Further investigation from the fundamental point of view is deserved.     

Corrosion resistance of compositionally modulated multilayered Zn–Ni alloys deposited from a single bath

By consecutive deposition at two different current densities from a single sulfate–chloride bath, compositionally modulated multilayered (CMM) coatings of Zn–Ni alloys, with different number, thickness and sequence of the sublayers were obtained. The corrosion resistance of the coatings was studied by potentiodynamic dissolution and by corrosion potential measurement. In the current–potential (stripping) curves two well-defined peaks were observed. With increase in the number of sublayers, regardless of their individual thickness, the correlation between the amount of Zn, dissolved at more negative potentials and the whole amount of the metal in the CMM coatings, decreases. The corrosion potentials of CMM coatings are most positive (–0.940 V vs SSE) when they end with a Zn–Ni18% oversublayer. As a result of the alternation of Zn–Ni alloy sublayers with different Ni content the obtained CMM coatings have increased corrosion resistance in comparison with the monolayer coatings of the composing alloys.     

Pitting and repassivation processes of Al---Zn---Mg alloys in chloride solutions containing sulphate

The mechanism of localized corrosion of Al—5.03%Zn—1.67%mg—0.23%Cu alloy submitted to different heat treatments (annealed (A); cold-rolled (ST); quenched (F); quenched and aged (B); and quenched in two stages and aged (C)) in NaCl, Na₂SO₄ and in NaCl---Na₂SO₄ solution has been studied by cyclic polarization (CP), open circuit potential measurements, chronocoulometry, SEM and EDX. The electrochemical results in NaCl were consistent with the assays of SCC resistance of alloys B and C previously reported in the literature. Sulphate addition to chloride solutions produced a considerable shift of the breakdown potential in the positive direction. However, the repassivation potential, much more reproducible than the latter, was only slightly shifted in the negative direction. The role of sulphate was related with the oxide presence, its incorporation in the film precluding significant chloride penetration. However, the film conductivity apparently increased with potential in the presence of sulphate, finally making pit propagation possible and resulting in a much more intense pitting attack.     

汽车用锌-钴合金的制备及其耐蚀性的研究

在汽车用软钢上电沉积制备锌-钴合金,并研究了沉积电位对锌-钴合金的成分、厚度及耐蚀性的影响。研究表明:锌-钴合金的电沉积过程属于异常共沉积。钴的电沉积属于扩散控制,沉积电位越负,锌-钴合金中钴的质量分数越低。在-1.8V下制备的锌-钴合金表面致密,具有优异的耐蚀性,其中钴的质量分数为12.5%。     

Influence of microstructure and composition on the corrosion behaviour of Mg/Al alloys in chloride media

The influence of the microstructure and aluminium content of commercial AZ31, AZ80 and AZ91D magnesium alloys was evaluated in terms of their corrosion behaviour in an aerated 3.5 wt.% NaCl solution at 25 °C. The corrosion process was monitored by electrochemical impedance spectroscopy (EIS). The surface was characterized by scanning electron microscopy (SEM), scanning Kelvin probe force microscopy (SKPFM) and low-angle X-ray diffraction (XRD). The extent of corrosion damage was strongly dependent on the aluminium content and alloy microstructure. Two key factors were observed for the lowest corrosion rates, which occurred for the AZ80 and AZ91D two-phase alloys: the aluminium enrichment on the corroded surface for the AZ80 alloy, and the β-phase (Mg₁₇Al₁₂), which acted as a barrier for the corrosion progress for the AZ80 and AZ91D alloys. Surface potential maps suggested that, between the β-phase and the α-matrix, the galvanic coupling was not significant.     

工业循环冷却水中不锈钢点蚀缓蚀剂的研究

采用极化曲线研究了钼酸钠、硫酸钠及硝酸钠对不锈钢在模拟高硬度高氯循环冷却水中点蚀的缓蚀作用.研究结果表明,三种无机缓蚀剂对不锈钢的点蚀均有不同程度的抑制作用,其效果随溶液温度变化而改变,在低温时,缓蚀作用顺序为硝酸钠＞硫酸钠＞钼酸钠;在高温时,缓蚀作用顺序为钼酸钠＞硫酸钠＞硝酸钠.     

醋酸的腐蚀特性及缓蚀剂

简要地介绍了碳钢、不锈钢、铜、铝及它们的合金在各种浓度的醋酸溶液中 ,在不同温度 (从室温到沸点 )时的腐蚀特性及一些缓蚀剂的缓蚀效率     

铝及其合金着色技术的研究进展

传统的铝及其合金着色技术主要包括化学染色法、整体染色法和电解着色法，新型的铝及其合金着色技术主要包括化学转化膜技术、电泳技术、微弧氧化陶瓷成膜技术、粉末静电喷涂技术。针对着色技术现存的主要问题，简述了铝及其合金着色技术的研究现状，包括电解着色机理，耐久性染料、新型稳定剂、特殊电源、多色化工艺的开发等，并展望了今后的研究趋势与发展方向。     

十二烷基硫酸钠对不锈钢在循环冷却水中的缓蚀作用

研究了在50℃含有氯离子的模拟循环冷却水溶液中,表面活性剂十二烷基硫酸钠对不锈钢点蚀行为的影响。实验结果表明,十二烷基硫酸钠对不锈钢的点蚀具有一定的缓蚀作用,且随其浓度的增大,缓蚀效果越好;当十二烷基硫酸钠的浓度为6mmol/L,θ为50℃时缓蚀效果最佳。     

Electrochemical behaviour of heat-treated AlZnMg alloys in chloride solutions containing sulphate

The electrochemical corrosion and passivation of Al5Zn1.7Mg0.23Cu0.053Nb alloys, submitted to different heat treatments (cold-rolled, annealed, quenched and aged, and quenched in two steps and aged), in sulphate-containing chloride solutions, has been studied by means of cyclic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS). The cyclic polarization curves showed that sulphate addition to the chloride solution produced a poor reproducible shift of the breakdown potential to more positive potentials. The repassivation potentials, much more reproducible, and practically separating the passive from the pitting potential region, were slightly displaced in the negative direction with that addition. When the alloys were potentiodynamically polarized in the passive potential region, sulphate was incorporated in the oxide film, thus precluding chloride ingress. In addition, Zn depletion was favoured, whereas Mg losses were avoided. Different equivalent circuits corresponding to different alloys and potentials in the passive and pitting regions were employed to account for the electrochemical processes taking place in each condition. This work shows that sulphate makes these alloys more sensitive to corrosion, increasing the fracture properties of the surface layer and favouring the pitting attack over greater areas than chloride alone.