A photo-electron and secondary ion mass spectrometric study of the chemical composition of thermal oxide layers on technically pure aluminium

The thickness and chemical composition of oxide films on aluminium of technical purity (Al 99.2–99.5) has been studied by photo-electron spectroscopy and secondary ion mass-spectrometry for differently prepared surfaces. Special emphasis has been placed in understanding quantitatively the oxidative surface enrichment processes of alkali and alkaline earth elements that take place during annealing at higher temperatures (250–340°C). The concentration of these elements (particularly those of lithium and magnesium) in the oxide layers of annealed foil samples is higher by a factor of 10³ to 10⁴ compared to the bulk metal contents. How these surface enrichment processes modify the chemical properties of the oxide film is discussed. An enhanced susceptibility of the surface to corrosion in the presence of humidity is found which can cause interfacial reactions and delamination problems in the case of lacquered foil.     

空调铝箔的高效脱脂剂

配制了一种空调铝箔的高效脱脂剂，通过耐碱性、耐盐蚀性等实验研究了脱脂时间、温度等因素对脱脂效果的影响，结果表明，该脱脂剂具有优良的脱脂效果：50℃脱脂25 min后，涂布防腐底漆，可达到空调铝箔的耐蚀要求.     

电解电容器用铝箔概述

讨论了电解电容器用电子铝箔的现状和发展方向。介绍了一些国内外电子铝箔的种类和牌号，电子铝箔和电极箔的一些特殊检测方法，如亮晶度法、残留铜分析法和氧化膜厚度估测法等。     

The role of chelating agents on the corrosion mechanisms of aluminium in alkaline aqueous solutions

The influence of 1,2-diaminoethane (DAE) on the mechanism of aluminium corrosion in KOH solutions at pH 13 was investigated by combining time-resolved inductively coupled plasma optical emission spectrocopy, open-circuit potential measurements and X-ray photoelectron spectroscopy. In pure KOH solutions, a very slow corrosion rate is initially observed, corresponding to the dissolution of the native oxide layer. Following this incubation stage, the corrosion rate is increasing due to the formation and oxidation of Al hydride, until a steady state is reached. DAE behaves as a strong initial corrosion accelerator, due to synergistic effects with hydroxyl ions and a dissolution mechanism in three successive steps has been proposed: (i) a rapid initial dissolution induced by the formation and detachment from the surface of bidentate (chelate) Al-DAE metal bound surface complexes; (ii) a slower step ascribed to the formation and release of monodentate Al-DAE metal bound surface complexes and (iii) a final step dominated by direct oxidation of surface aluminium hydride by hydroxyl species as in pure KOH.     

Oxide scale formation on Al containing Ni–Cr‐based high temperature alloys during application as flame tube material in recirculation oil burners

The flame tube is an important functional component of burners using the concept of the flame tube stabilised combustion. Under typical combustion conditions the material of the flame tube is exposed to high temperatures (≥900 °C) and to corrosion attack by the combustion gases. Furthermore as the burners are generally operated intermittently, the material suffers from extreme temperature and atmosphere changes. For flame tubes, a lifetime of approximately 8000 h is desired. Predominantly metallic high temperature materials are used. The scope of the present work was to test—under application conditions and for maximum material temperatures exceeding 900 °C—alternative high temperature alloys for use as tube material. The corrosion resistance of the austenitic Ni–Cr‐based alloys (601, 602 CA, 617 and 693) has been investigated in a burner rig at maximum material temperatures of 950 and 1000 °C and with exposure times from 50 to 3000 h. The chromium content of the alloys was between 20 and 30 wt% and that of aluminium between 1 and 3.4 wt%. Metallographic cross‐sections of samples of the alloys were analysed by electron microprobe yielding information about the microstructure and composition of the oxides in the surface zone and variations during exposure time. This study focuses on the observed specific effects of the alloying element aluminium on the development of the oxide scale and on the lifetime of the alloys. At the alloy surface after 500 h exposure time a chromium oxide scale had formed with aluminium oxides underneath predominantly along grain boundaries. For the alloys with the lower aluminium content, the aluminium oxides built up an open network but not a closed layer. For the alloy with the highest aluminium content (alloy 693) after 50 h two different characteristic microstructures at the surface were found. In one case, the grains at the surface were covered with chromium oxide on top and the remaining grain surface was completely enclosed by aluminium oxides. In the other case, the aluminium oxide formed a thin layer directly below the chromium oxide scale. After 500 h exposure time, a significantly thinner chromium oxide scale and massive internal chromium oxides were observed. Catastrophic corrosion, formation of internal oxides and aluminium nitrides started even after 500 h. It will be demonstrated that the early breakdown of alloy 693 is linked to the aluminium oxides which act as a barrier constricting the diffusion of chromium from the alloy matrix towards the surface. Under the conditions of extreme temperature changes given in the burner the aluminium oxide layer on its part did not provide corrosion protection.     

Corrosion and electrochemical behavior of aluminium treated with high-temperature pulsed plasma in CsCl–NaCl–NaNO3 melt

Dense protective layers of aluminium corrosion products, whose composition depends on the oxidation temperature, are formed on the surface of aluminium treated with high-temperature pulsed plasma (HTPP) without visible remelting and then held in a chloride–nitrate melt in conditions of anodic polarization. Modification of aluminium treated with HTPP changes the properties of 20 μm layer under its surface and the oxide layer formed by such treatment has different morphology: it consists of smaller crystals and so has the other protective properties as compared with aluminium untreated by plasma.     

Corrosion behaviour of Nickel-aluminium alloys in molten carbonate

The corrosion behaviour of nickel-aluminium alloys with aluminium contents of 2-50%, in molten carbonate has been investigated with electrochemical techniques in combination with post-test analysis of quenched specimens. For the 2 to 10% aluminium alloys a type of aluminium oxide is formed along the grain boundaries of the base metal at potentials of -1100 and -900 mV. At potentials of -700 nmV and more anodic an outer oxide scale is formed and also aluminium oxide formation takes place along the grain boundaries. The oxide scale contained nickel, aluminium and oxygen. The only corrosion product that could he detected by X-ray diffraction on specimens quenched after polarisation at -700 mV or more anodic is NiO; no type of aluminium oxide could be detected, probably due to the small amount of aluminium oxide formed. For the 20% aluminium alloy a type of aluminium oxide is formed along the grain boundaries at -1100 and -900 mV. After longer polarisation times also the aluminium in the interior of the grains is oxidised, which results in a two-layer microstructure: an outer layer of pure nickel, and an inner layer that is a honeycomb network of nickel filled with aluminium, oxygen and nickel, while high amounts of aluminium and oxygen could be detected along the grain boundaries. The amount of corrosion product was too small to be detected by X-ray diffraction. At potentials of -700 mV and more anodic, an oxide scale of irregular thickness is formed, but no oxide could be observed along the grain boundaries. The only corrosion product detected by X-ray diffraction on specimens quenched after polarisation at potentials in this range is nickel oxide. On the 50% aluminium alloy a continuous oxide layer is formed at all potentials. The only corrosion product formed at all potentials is α-LiAlO₂; the stable form of LiAlO₂ is γ-LiAlO₂. α-LiAlO₂ is probably an intermediate product that is slowly transformed to γ-LiAlO₂. The oxide layer provides good protection against further corrosion of the base material. The quasi-stationary polarisation curves are very similar to those of pure nickel, because no protective oxide scales are formed on the 2 to 20% aluminium alloys during preconditioning at -1100 mV.     

2A12铝合金微弧氧化膜电化学腐蚀性能研究

采用微弧氧化技术对粉末冶金制备的2A12铝合金进行表面改性,表征改性层微观结构和相组成,评价改性后2A12铝合金的电化学腐蚀性能。研究发现:微弧氧化处理之后,2A12铝合金表面生成厚度约为80 μm的均匀氧化膜,其主要由α-Al₂O₃、γ-Al₂O₃及非晶组织构成;采用微弧氧化对2A12铝合金表面改性之后,改性层极大程度地抑制合金表面阳极反应和阴极反应的进行,自腐蚀电流密度明显下降,腐蚀速率显著降低,合金电化学腐蚀性能明显提高。     

少量金属元素对Al—Zn共晶合金钎焊点抗腐蚀性能的影响

用经典失重法和显微结构法研究了20个少量添加元素对纯铝及LY-12母材上Al-Zn钎料焊点抗腐蚀性能的影响。发现添加少量碱土金属或稀土金属能有效地提高焊点的抗腐蚀性。少量重金属Bi,Sn,Pb,Cd,Tl,Cu,Ni及Ga等引起合金强烈的晶间腐蚀。过渡金属及碱金属影响不大。     

Anwendung der röntgenografischen Verbundanalyse bei der Schadenaufklärung

Application of composite radiographical methods of analysis to the investigation of cases of damage On the strength of numerous examples, it is shown that the combination of the X-ray fluroescence analysis with the X-ray microstructure analysis represents an important aid in investigating cases of damage as the corrosion products are analyzed not only in regard to their composition but also in regard to the type of compound. The following causes of corrosion have been diagnosed in this way: — Sedimentation of catalyst particles and of entrained dissolved products from the boiler water; temperature below condensation point; effects of potassium sulphate and/or aluminium ortho-arsenate or of vanadium compounds from fuel oil; wet cleaning with ammonia water before commissioning a boiler; effect of alkali and alkaline earth oxides on the brick lining of a combustion chamber; deficiency of iron sulphate as a cause of deficient cover layers on brass; effect on galvanized parts of the HCL formed during the combustion of PVC.     

The Initial Stages in the Oxidation of TiAl

The oxidation behaviour of titanium aluminides containing 36 wt.-% Al (Ti36Al) and 35 wt.-% Al plus 5 wt.-% Nb (Ti35Al5Nb) has been investigated by electron microscopic methods with emphasis on transmission electron microscopy (TEM). The oxidation experiments were carried out at 800 to 1000°C in laboratory air for 0.5 h to 4 h. In addition thermogravimetric measurements were made. It has been shown that the shortterm oxidation of TiAl can be divided into two stages. In stage I the preferred formation of aluminium oxide leads to an aluminium depletion of the metal subsurface zone and the subsequent formation of titanium nitrides which enhances the oxidation rate. After consumption of the depletion layer a repeated cycle of aluminium oxide formation, subsequent local depletion of the metal subsurface zone in Al and consumption of the Ti-rich metal phase by nitride formation is observed leading to linear oxidation behaviour (stage II). In the niobium containing alloy the dissolution of alumina in titania is decreased and thus the formation of aluminium oxide at the metal/oxide interface is favoured. By electron diffraction it has been found that the aluminium oxide formed at the metal/oxide interface most probably is an aluminium oxynitride Al₂₇O₃₉N. The aluminium depleted metal phase has been analyzed to consist of α₂-Ti₃Al and a new cubic phase with a composition between of α₂-Ti₃Al and γ-TiAl.     

Cathodic polarization of commercially pure aluminium

Cathodic corrosion, particularly alkaline pitting and repassivation, of 1S aluminium has been investigated by potential-controlled methods in unbuffered chloride media. The results are mainly for de-aerated solutions; the influence of dissolved oxygen and stirring, which are likely to be present in a practical situation, are also discussed. The metal undergoes stable pitting and then uniform etching as the applied potential is decreased below ? 1.35 V(SCE). At potentials more positive than this threshold value, metal dissolution still occurs possibly near the cathodic impurities on the surface due to local alkalinization resulting from hydrogen evolution; but, the surface repassivates slowly as the cathodic sites are covered up by the oxide film. The polarization behaviour of the partially passive surface is studied by fast-scan potential measurements and is associated with hydrogen evolution kinetics. The measured current decays exponentially with time during repassivation at constant potential. This is explained in terms of a model based on film growth controlled by metal dissolution.     

Cathodic polarization of commercially pure aluminium

Cathodic corrosion, particularly alkaline pitting and repassivation, of 1S aluminium has been investigated by potential-controlled methods in unbuffered chloride media. The results are mainly for de-aerated solutions; the influence of dissolved oxygen and stirring, which are likely to be present in a practical situation, are also discussed. The metal undergoes stable pitting and then uniform etching as the applied potential is decreased below — 1.35 V(SCE). At potentials more positive than this threshold value, metal dissolution still occurs possibly near the cathodic impurities on the surface due to local alkalinization resulting from hydrogen evolution; but, the surface repassivates slowly as the cathodic sites are covered up by the oxide film. The polarization behaviour of the partially passive surface is studied by fast-scan potential measurements and is associated with hydrogen evolution kinetics. The measured current decays exponentially with time during repassivation at constant potential. This is explained in terms of a model based on film growth controlled by metal dissolution.     

泡沫铝阳极氧化工艺研究

介绍泡沫铝阳极氧化工艺。通过试验分析对比WL-SY酸蚀工艺和碱蚀工艺的差异,探讨泡沫铝阳极氧化过程中硫酸浓度、电流密度、温度、Al3＋浓度、时间、杂质元素对阳极氧化膜的影响。     

Electrochemische Untersuchungen zur Hochtemperaturkorrosion von Chromstählen in Alkalisulfatschmelzen

Electrochemical investigation into the high temperature corrosion of chromium steels in alkali sulfate melts Electrochemical and corrosion-chemical investigations have been carried out with scaling resistant chromium steels, iron, chromium and platinum in a eutectic (Li, Na, K)₂-SO₄. It has turned out that sufficiently exact data concerning corrosion reactions can be obtained only from mass losses, not, however, from current density. The corrosion behaviour depends from potential. Comparable to the conditions in aqueous solutions potential ranges exist with passive and transpassive corrosion and with a rupture potential which depends from the chromium content of a steel. Protective oxide layers exist in the passive range where the mass loss becomes almost constant after a certain in cubation period. In the transpassive range corrosion follows an almost parabolic law with formation of an inner sulfide layer and a thicker external oxide layer where chromium is enriched. These layers are largely formed by oxidizing media carried to the metal surface via sulfur oxides; during this reaction inert marks in the steel remain unchanged. Sulfur oxides may be formed as secondary consecutive products by reactions between metal ions and sulfates. The solubility of metal ions in the sulfate melt is an important parameter for corrosion rates. Oxide ions (as reduction products of O₂) act as inhibitor on the anodic partial reaction, while SO₃ and ferric ions have a large lating effect, so that the anodic dissolution is autocatalyzed. Chlorides, too, act as stimulators in the transpassive range. Corrosion at the free corrosion potential is largely controlled by ferric ions which act as anodic and cathodic stimulators in acid melts. In neutral melts under oxygen an 18% chromium steel is passive.     

Effect of titanium addition on corrosion properties of Al-Si eutectic alloys

Aluminium and its alloys are the most used non-ferrous metals because of their satisfactory properties. Especially the corrosion resistant in different mediums is the most important reason for this. The corrosion resistance of the aluminium comes from the oxide layer on the surface. Different alloying elements have different effect on corrosion behaviour of the aluminium alloys. In this study effect of different amount of titanium addition on corrosion behaviour of Al-Si eutectic alloys was investigated.     

Multilayered coatings: Tuneable protection for metals

The role of oxide bi-layers in controlling the onset of corrosion has been explored. A high-throughput electrochemical approach was employed to determine the breakdown potential of aluminium metal over-coated with combinations of silicon, titanium, aluminium and magnesium oxides. Bi-layered coatings consisting of two 100 nm thick metal oxide layers provided increased protection against breakdown, and combinations with vastly different iso-electric point of solid (IEPS) were found to exhibit improved barrier properties in comparison to single-component oxides. Furthermore, the most protective oxide bi-layers were produced when a high IEPS oxide was deposited directly onto the metal surface and subsequently over-coated with a low IEPS oxide. The barrier properties of bi-layer coatings appear to be tuneable, with notable dependencies on surface charge and thickness.     

泡沫铝阳极氧化工艺研究

介绍了泡沫铝阳极氧化工艺,通过试验对比分析了KD-SY酸蚀工艺和碱蚀工艺的差异,探讨了泡沫铝阳极氧化过程中,硫酸浓度、电流密度、温度、Al3+浓度、杂质元素对阳极氧化膜的影响.     

Morphology and corrosion characteristics of laser surface remelted Al‐Si alloy at cryogenic conditions

The properties and consequently functionality of equipment made of aluminium alloys are influenced by microstructural characteristics such as phase composition and grain size distribution in their surface layer. Nowadays, many surface engineering techniques have been applied to improve the surface properties of aluminium alloys, one of them being laser surface treatment. The effect of laser surface remelting at cryogenic conditions on the local chemical compositions, microstructure and corrosion characteristics of AlSi13Mg1CuNi aluminium alloy have been presented. The beneficial effect of laser treatment on the corrosion behaviour of the cast aluminium alloy in 0.01 M sulphuric acid solution was observed.     

稀土铝合金热浸镀渗工艺研究

对稀土铝合金的热浸镀渗工艺及渗铝后的耐腐蚀性进行了研究。结果表明，稀土对于热浸镀渗铝具有良好的催渗作用。钢表面热浸镀渗稀土铝后，具有良好的耐腐蚀性，其中含0．3％LPC混合稀土的铝合金具有更好的耐腐蚀性，其耐腐蚀性3倍于纯铝。