Corrosion of aluminium and aluminium alloy in ethylene glycol–water mixtures

Samples of pure aluminium and aluminium alloy were heated at 150 kPa and 130 °C in ethylene glycol (EG)–water mixture (volume ratio 1:1) for 172 h (8–12 h heating, 12–16 h pause). The corrosion of the metals was characterised by the transfer of Al into solution, changes in the surface morphology of the samples and their electrochemical behaviour. Formation of a white crystalline aluminium-organic precipitate was found during the heating of metals and some of its characteristics were determined. The effect of the addition of glycolic, citric and sebacic acid to the EG–water mixture on the metal corrosion behaviour was investigated. A significant corrosive action of glycolic acid and a protective effect of sebacic acid were found.     

Nd对锌电积用Pb-Ag合金阳极性能的影响

采用恒流极化、失重法和抗拉强度测试研究不同含量Nd的加入对锌电积用铅银合金阳极主要性能(稳定阳极电位、耐腐蚀性能及力学性能)的影响,并在此基础上采用循环伏安(CV)和计时电位(CP)等电化学手段对恒流极化条件下Nd的作用机理进行研究。结果表明:0.03%Nd(质量分数)加入可以将Pb-Ag合金的抗拉强度提高21.8%;锌电积条件下,铅阳极表面腐蚀膜主要成分为PbO2及PbSO4,Nd加入可以抑制PbSO4的形成,从而明显降低阳极腐蚀速率;由于Nd能降低析氧过电位,且对高阻抗PbSO4的生成具有抑制作用,使得Pb-Ag合金的阳极电位亦有一定程度的下降。Nd对锌电积阳极主要性能均有较大程度的改进作用,是很好的锌电积阳极改性剂,具有较好的工业应用前景。     

Fatigue crack propagation in an aluminium alloy at 223 K

The fatigue crack growth behaviour of a naturally aged aluminium alloy has been investigated at 223 K. Crack growth rates in a cold environment are shown to be slower than in ambient air, which is associated with a crystallographic crack path. Results are discussed on the basis of work previously proposed [Petit J, Hénaff G, Sarrazin-Baudoux C. Fracture of materials from nano to macro. In: Milne I, Ritchie RO, Karihaloo B, editors. Comprehensive Structural Integrity, vol. 6. Oxford: Elsevier; 2003. p. 211.].     

大型铝电解惰性阳极的研制

本文报导了新近研制开发的大型铝电解惰性阳极板(160×100×10mm)的制作过程,并对使用的原料准备、压制成型、烧结过程进行讨论。该阳极板可拼接为160×300~500×10mm大型阳极并组装为3000~6000A铝电解试验槽的惰性阳极。     

Influence of aluminium and lead on activation of magnesium as anode

Mg-6%Al,Mg-5%Pb and Mg-6%Al-5%Pb (mass fraction)alloys were prepared by induction melting with the protection of argon atmosphere.Their electrochemical activations in different electrolyte solutions were investigated by galvanostatic test.The microstructures of these alloys and their corroded surfaces were studied by scanning electron microscopy,X-ray diffractometry and emission spectrum analysis.The results show that the activation of magnesium is not prominent when only aluminum or lead exists in the magnesium matrix,but the coexistence of the two elements can increase the activation.The activation mechanism of Mg-Al-Pb alloy is dissolving-reprecipitating and there is a synergistic effect between aluminium and lead:the precipitated lead oxides on the surface of the alloy can facilitate the precipitation of Al(OH)3,which can peel the Mg(OH)2 film in the form of 2Mg(OH)2·Al(OH)3 and activate the magnesium matrix.     

Cathodic protection of steel in concrete using magnesium alloy anode

Corrosion of steel embedded in concrete structures and bridges is prevented using cathodic protection. Majority of the structures protected employ impressed current system. Use of sacrificial system for the protection of steel in concrete is not as widely employed. The use of magnesium anodes for the above purpose is very limited. This study has been carried out with a view to analyse the use of magnesium alloy anode for the cathodic protection of steel embedded in concrete.Magnesium alloy anode, designed for three years life, was installed at the center of reinforced concrete slab, containing 3.5% sodium chloride with respect to weight of cement, for cathodic protection. Potential of the embedded steel and the current flowing between the anode and the steel were monitored, plotted and analyzed. Chloride concentration of concrete at different locations, for different timings, were also determined and analyzed.The magnesium anode was found to shift the potential of the steel to more negative potentials initially, at all distances and later towards less negative potentials. The chloride concentration was found to decrease at all the locations with increase in time. The mechanism of cathodic protection with the sacrificial anode could be correlated to the removal of corrosive ions such as chloride from the vicinity of steel.     

Influence of magnesium nitrate on the corrosion performance of sol-gel coated AA2024-T3 aluminium alloy

Traditional anticorrosion technology has relied heavily on using reducible metal species, predominantly hexavalent chromium (Cr(VI)), for protecting reactive metal alloys such as aluminium which is extensively used in the aerospace sector. However, the impending changes in the use of Cr(VI) in Europe and the United States have forced aerospace manufacturers to examine alternative materials for protecting aluminium. One of the most promising alternatives being investigated are organosilane based sol-gels containing anticorrosion additives. In this work the anticorrosion properties of magnesium (II) nitrate (Mg(NO₃)₂) as an inhibitor were investigated at different concentrations (0.1%-1.0 wt.%) in a methyltrimethoxysilane (MTEOS) sol-gel on the aluminium alloy AA 2024-T3 and compared to Alodine^TM 1200 (the established Cr(VI) pre-treatment). Electrochemical evaluation of the coating system by electrochemical impedance spectroscopy (EIS) and potentiodynamic scanning (PDS) measurements correlated strongly with results obtained from Neutral Salt Spray (NSS) exposure data. The surface morphology of the coating was studied using atomic force microscopy (AFM) and scanning electron microscopy (SEM) and Energy Dispersive X-ray Spectrometry (EDS). The results indicated that the optimum performance was achieved with a Mg (NO₃)₂ level of 0.7% w/w. It is proposed that the superior anticorrosion properties of the Mg²⁺ rich sol-gel are due to the pore blocking mechanism of insoluble magnesium precipitates formed during the hydrolysis process.     

Rare earth chloride and nitrate salts as individual and mixed inhibitors for aluminium alloy 7075-T6 in chloride solution

The aim of the study was to investigate various rare earth salts as corrosion inhibitors of aluminium alloy 7075-T6. Rare earth salts, CeCl₃, LaCl₃, Ce(NO₃)₃ and La(NO₃)₃, were studied, first as individual inhibitors in the concentration range between 0.001 and 0.05?M. Second, the inhibitory effect of mixtures of chloride or nitrate salts was studied at an overall inhibitor concentration of 0.01?M. The corrosion properties of AA7075-T6 in the absence and presence of individual and mixed rare earth salts were investigated using electrochemical potentiodynamic technique in 0.1?M NaCl. The topography, morphology and composition of the inhibited surfaces were recorded. The highest inhibitory effectiveness was exhibited by CeCl₃, followed by mixtures of CeCl₃ and LaCl₃. During immersion for 12?h the corrosion protection remained high. Nitrate rare earth salts showed less protection, both as individual or as mixed inhibitors. Deposits containing both cerium and lanthanum were formed primarily on Cu-based intermetallics.     

Triazole and thiazole derivatives as corrosion inhibitors for AA2024 aluminium alloy

The 1,2,4-triazole, 3-amino-1,2,4-triazole, benzotriazole and 2-mercaptobenzothiazole were evaluated in the present work as corrosion inhibitors for protection of the 2024 aluminium alloy in neutral chloride solutions. The corrosion protection performance was investigated by means of DC polarization and electrochemical impedance spectroscopy (EIS). Scanning Kelvin probe force microscopy (SKPFM) and atomic force microscopy (AFM) were used to study the evolution of the Volta potential distribution and the surface topography during corrosion tests.The results show that all inhibitors under study confer corrosion protection to the AA2024 alloy forming a thin organic layer on the substrate surface. Benzotriazole and 2-mercaptobenzothiazole offer better corrosion protection in comparison with the other two. The inhibitors studied act decreasing the rate of both the anodic and cathodic processes. In the latter case the dealloying of the copper-reach particles is hindered, slowing down the oxygen reduction.     

Corrosion of an Al-Zn-In alloy in chloride media

In order to explain the electrochemical behaviour of Al-Zn-In based alloys in chloride media, a commercial Al-Zn-In-Si anode and a ternary alloy, Al-5%Zn-0.02%In prepared in our laboratory, were investigated using potentiodynamic techniques, complemented by SEM, EDX and TEM. The influence of alloy composition, agitation and previous cathodisation on the electrochemical response of the alloys was analysed. Results of previous investigations with pure metals (Zn and In) and with binary alloys (Al-In, In-Al, Zn-In) are also considered in this paper for the sake of comparison. The attack initiation on the Al-Zn-In alloy is related to In-Zn rich zones, segregated at grain boundaries. The presence of In in true electric contact with Al and Zn promotes Cl⁻ adsorption at potentials more positive than −1.1 V. Then, the presence of Zn facilitates a surface enrichment of indium by a displacement reaction. This in turn, assures an accumulation of adsorbed Cl⁻, which maintains an active state of the Al matrix.     

Corrosion resistance of cerium‐based chemical conversion coatings on AA5083 aluminium alloy

In this paper the effect of several parameters, such as temperature, time of immersion, cerium ions and hydrogen peroxide concentration, pH of the conversion solution, on the composition and morphology of the conversion layer are investigated as well as on its corrosion resistance in chloride environments. The cerium‐based chemical conversion coatings ennobles the corrosion potential and inhibits both the cathodic and anodic reactions rate. Using a cerium (III) chloride solution a not homogeneous coating is obtained and agglomerates with a “dry‐mud” morphology of mixed cerium‐aluminium oxide are deposited above the cathodic intermetallic particles, while using a cerium (III) nitrate solution the coating is more uniform but thinner than that obtained with cerium (III) chloride. Solution temperature below 50°C and time of immersion of 10 minutes produces a coating with better corrosion resistance.     

Polyoxadiazole-based coating for corrosion protection of magnesium alloy

In this study, polyoxadiazole-based coatings were molecularly designed by attaching two different functional groups, i.e., diphenyl-ether and diphenyl-hexafluoropropane, in the main polymer chain for the purpose of low water permeability and eventually for high corrosion protection of AM50 magnesium alloy. Potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) were used to evaluate the coating performance of the two polymers. Electrochemical experiments showed that POD-6FP (poly(4,4′-diphenyl-hexafluoropropane-1,3,4-oxadiazole)) coated alloy exhibited 3-4 orders of magnitude higher corrosion resistance as compared to the POD-DPE (poly (4,4′-diphenyl-ether-1,3,4-oxadiazole)) coated alloy. The high coating performance of the POD-6FP polymer can be attributed to the hydrophobic group attached to the polyoxadiazole chain.     

The adhesion properties and corrosion performance of differently pretreated epoxy coatings on an aluminium alloy

The influence of various blends of hexafluorozirconic-acid (Zr), polyacrylic-acid (PAA) and polyacrylamide (PAM) pretreatment on the performance of an epoxy coated aluminium substrate was investigated and compared to that of a so-called chromate/phosphate conversion coating (CPCC).Adhesive-strength of epoxy coated substrates was evaluated using pull-off and tape tests. Salt spray, humidity chambers and EIS were employed to characterize corrosion performance of coated substrates with different initial surface pretreatments. Among the Zr-based formulations, PAA/Zr and PAA/PAM/Zr showed the best adhesion strength, while the later revealed a good corrosion performance as well. However, CPCC pretreated sample was still superior in these aspects.     

Effect of adding potassium hydroxide to an agar binder for use as the anode in Zn–air batteries

Agar–KOH was used for the Zn-powder binder at different concentrations in order to achieve the desired conductivity and physical properties. The presence of KOH causes the growth of a ZnO needle structure that covers the Zn-active materials. The formation of ZnO is proven by microscopy and structural measurements. To further understand the effect of KOH in the agar binder, Zn–air batteries are fabricated. The results show that the Zn–agar binder without KOH gives the highest discharge capacity of 505.0 mA h g⁻¹. The results contradict earlier expectations that a ‘small’ amount of KOH in agar could increase the battery’s capacity.     

Structure and high-temperature oxidation behaviour of Cu-Ni-Fe alloys prepared by high-energy ball milling for application as inert anodes in aluminium electrolysis

Cu_xNi_85−xFe₁₅ (0 ? x ? 85 wt.%) compounds were prepared by mechanical alloying. Monophased face centered cubic (fcc) Cu-Ni-Fe alloys were obtained after 10 h of milling for x varying from 0 to 50, whereas bi-phased compounds fcc Cu-Ni-Fe + body centered cubic (bcc) Fe were formed with richer-Cu compounds. Their oxidation kinetics in air at 750 °C is parabolic for all compositions and increases drastically for x > ∼30. A stable anode for aluminium electrolysis in low-temperature (700 °C) KF-AlF₃ electrolyte was obtained for 65 ? x ? 85. However, a substantial increase of the Cu contamination in produced aluminium was observed for x > 70.     

Sulfidation behavior of a binary Fe-Mn alloy

An Fe-27 w/o (weight %) Mn alloy was sulfidized at temperatures of 973, 1073, and 1173 K inflowing H₂/H₂S/N₂ atmospheres corresponding to equilibrium sulfur pressures of 8 Pa. Steady-state parabolic kinetics were always observed after an initial period during which the instantaneous parabolic rate constant increased with time. Product scales were compact and consisted of a layer of Fe(Mn)_1–x S over an inner layer of -Mn(Fe)S. Preoxidation led to a diminution in the subsequent sulfidation rate. Conflicts between differing reports in the literature of the kinetics of this reaction are resolved, and it is concluded that the protective effect expected of an -MnS layer is in fact possible.     

Electrodeposition and characterization of zinc-cobalt alloy from chloride bath; influence of coumarin as additive

Zinc-cobalt alloys were electrodeposited from chloride bath under continuous current and in the presence and absence of coumarin. The deposit morphology was analyzed using Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD) was used to determine the preferred crystallographic orientations of the deposits. Zinc-cobalt alloys was without texture in the absence of coumarin whereas, the preferred crystallographic orientations was (103) at 65% in the presence of coumarin. The presence of coumarin yields deposits with a finer grain size. The alloy composition was examined using the Energy Dispersive X-ray Fluorescence Spectroscopy (EDXRF). The percentage of cobalt in the alloy decreases from 1.04 wt.% to 0.69 wt.% in the presence of coumarin. Voltammetric studies show that coumarin affects the reduction of zinc but it was without effect on cobalt reduction. That explains the decrease of cobalt percentage in the alloy in the presence of coumarin.     

The high throughput assessment of aluminium alloy corrosion using fluorometric methods. Part I - Development of a fluorometric method to quantify aluminium ion concentration

This paper examines a new method developed for the rapid assessment of corrosion inhibitors and their combinations for aluminium alloy 2024-T3 (AA2024-T3). Two fluorometric probes, lumogallion and morin, were used to rapidly assess the concentration of aluminium ions in solution through the use of a spectrophotometric plate reader. Fourteen potential inhibitor compounds and other assay constituents were screened for fluoroprobe interference: sodium chromate, sodium metavanadate, cerium chloride, lanthanum chloride, europium chloride, gadolinium chloride, neodymium chloride, yttrium chloride, barium metaborate, sodium metatungstate, potassium phosphate, sodium metasilicate, sodium phosphate, and sodium molybdate. Calibration curves were established for the two probes.     

A chrome-free conversion coating for magnesium-lithium alloy by a phosphate-permanganate solution

A chrome-free conversion coating on magnesium-lithium alloy was obtained from a phosphate-permanganate solution. The morphology, the composition and the corrosion resistance of this coating were examined. The thin and non-penetrating cracked morphology with some deposits existed on the phosphate-permanganate conversion coating. The main elements of the conversion coating were Mg, O, K, P and Mn. The results of the electrochemical measurements and the immersion tests demonstrated that the corrosion resistance of the magnesium-lithium alloy has been improved by the phosphate-permanganate conversion treatment.     

高性能锂离子电池负极材料CoO/石墨烯纳米复合结构的超声法制备(英文)

以羰基钴为原料,采用简易超声法制备氧化亚钴和石墨烯纳米复合结构。通过扫描电子显微镜(SEM)、透射电子显微镜(TEM)及光电子能谱(XPS)对该纳米复合结构进行表征。结果表明:粒径为3~5nm的氧化亚钴纳米颗粒均匀分布于石墨烯表面。将氧化亚钴/石墨烯纳米复合结构用作锂离子电池负极材料,电化学测试结果表明,该复合结构具有高电容量(50次循环后电容量为650mA·h/g,约是商用石墨电极的2倍)、高库伦效率(高于95%)以及很好的循环稳定性。该优异的电化学性能源于氧化亚钴/石墨烯纳米复合结构的特点:纳米尺寸的氧化亚钴颗粒分散于导电的石墨烯衬底上,有利于锂离子的嵌入和脱嵌,缩短了锂离子的扩散路径,提高了氧化物的导电性,从而改善了材料的电性能。