Investigations of burning phenomena during the hard anodising of aluminium by local  in-operando  temperature measurements

Lämmel, C.; Schneider, Michael; Heubner, Christian; Beckert, W.; Michaelis, Alexander

doi:10.1016/j.electacta.2017.07.167

Cited by 27 publications

(20 citation statements)

References 23 publications

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“…A basic constraint that limits access to certain benefits of the process is the amount of heat generated during formation of the alumina, related with the Joule’s effect. Reaching the critical point may result in the electric breakdown that can lead to the destruction of the sample [ 107 ]. The discovery of Lee and co-workers renewed the attention to HA [ 24 ].…”

Section: Nanoporous Anodic Alumina (Naa): Definition and Formationmentioning

confidence: 99%

Recent Advances in Nanoporous Anodic Alumina: Principles, Engineering, and Applications

2021

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The development of aluminum anodization technology features many stages. With the story stretching for almost a century, rather straightforward—from current perspective—technology, raised into an iconic nanofabrication technique. The intrinsic properties of alumina porous structures constitute the vast utility in distinct fields. Nanoporous anodic alumina can be a starting point for: Templates, photonic structures, membranes, drug delivery platforms or nanoparticles, and more. Current state of the art would not be possible without decades of consecutive findings, during which, step by step, the technique was more understood. This review aims at providing an update regarding recent discoveries—improvements in the fabrication technology, a deeper understanding of the process, and a practical application of the material—providing a narrative supported with a proper background.

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Section: Nanoporous Anodic Alumina (Naa): Definition and Formationmentioning

confidence: 99%

Recent Advances in Nanoporous Anodic Alumina: Principles, Engineering, and Applications

2021

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“…Assuming a current density of 500 mA cm −2 and an oxide thickness of 200 μm, the calculated value for the stationary H + concentration at the pore bottom equals to 3.6 mol L −1 which corresponds to an increase from pH −0.2 to pH −0.6. Due to this pH shift, a change in the oxide morphology can be expected, local dissolution might take place, and the probability of burning increases . To avoid such critical situations, pulse anodizing might be a suitable tool.…”

Section: Resultsmentioning

confidence: 99%

“…Due to this pH shift, a change in the oxide morphology can be expected, 14 local dissolution might take place, and the probability of burning increases. 10 To avoid such critical situations, pulse anodizing might be a suitable tool.…”

Section: Resultsmentioning

confidence: 99%

“…In previous investigations, the authors investigated the impact of electric field strength and the local heat development on the oxide properties. For example, it was shown that high local heat impact and thus structural destruction of the oxide can be avoided by targeted pulse anodizing . Additionally, it was found that an adjustment of the pulse parameters leads to a notable reduction of energy consumption during anodizing …”

Section: Introductionmentioning

confidence: 99%

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Development of the local proton concentration during pulse anodizing

Lämmel

Heubner

Schneider

et al. 2018

Surface & Interface Analysis

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The literature describes various beneficial effects of the pulse anodizing of aluminum related to the corrosion resistance, hardness, and electronic properties of the oxide layer, the thermal impact during the anodizing process as well as reduced energy consumption. In spite of the considerable improvements, the understanding of basic mechanisms and the specific impact of the applied pulse parameters are still under discussion. Herein, the local development of the electrolyte concentration during pulse anodizing in sulfuric acid is investigated by means of finite element computations. The impact of the thickness of the porous oxide, the applied current density, and the pulse frequency are examined systematically. The results suggest that the electrolyte concentration at the oxide/electrolyte interface can be effectively controlled by applying tailored pulse parameters.

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“…For example, when anodizing at 50 mA at a voltage of 25 V, 1.25 W are continuously dissipated due to Joule heating, which is the main heat source. 26,27 This is equivalent to approximately 18 cal/min, an amount of energy sufficient to raise by a fraction of a degree the temperature in the oxygen-collecting cylinder. Thus, if some heat is produced in the proximity of the electrode and transmitted to the evolving bubbles and to the collected gas (assuming that the heat capacity of the gas is negligible compared to that of the liquid) a significant variation in the buoyancy force can be generated due to the expansion of the gas in the collecting cylinder.…”

Section: Discussionmentioning

confidence: 99%

Gravimetric Measurement of Oxygen Evolution during Anodizing of Aluminum Alloys

Torrescano-Alvarez

Curioni

Skeldon

2017

J. Electrochem. Soc.

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A gravimetric method based on changes in buoyancy force of a submerged gas-collecting container has been optimized to measure the evolution of oxygen during anodizing of an aluminum alloy. Previously, the gravimetric method has been used to measure hydrogen evolution from magnesium and aluminum during corrosion processes, either at the free corrosion potential or under relatively low polarization. However, during anodizing, the comparatively higher values of current applied and the heating effects associated with power dissipation might introduce artefacts in the gas measurement. Optimization of the experimental setup enabled reduction or elimination of such artefacts, so that a reliable measurement could be obtained. The results show that typically about 15 to 20% of the current applied to an AA 2024-T3 aluminum alloy during anodizing in sulfuric acid under the present conditions was used in generating oxygen. Anodic treatments are commonly used to produce protective oxide films and coatings on metals such as aluminum, magnesium, titanium and their alloys. During such processes, in addition to the electrochemical oxidation of the substrate that produces the desired protective layer, oxygen may be generated electrochemically as a side reaction.1-5 For aluminum, oxygen generation during anodizing can be significantly increased by the addition of certain alloying elements or by the presence of impurities in the substrate, such as, for example, copper and iron.6,7 The oxygen may be formed at locations of intermetallic particles, where the high concentration of alloying elements locally modifies the composition, morphology and electronic properties of the oxide.2 Oxygen can also form above the matrix regions, when elements such as iron or copper in solid solution are oxidized and their ions incorporated into the oxide. The resultant modifications of the oxide properties enable the reactionto proceed within the oxide resulting in the development of nanobubbles of oxygen gas within the anodic film. 7Owing to the plasticity of the amorphous alumina during the growth of the film, 8,9 and the high pressure of the contained oxygen gas, 7 the bubbles are able to grow within the film until the film eventually ruptures and the gas is released to the electrolyte.7,10 The liberation of oxygen has been proposed to account for changes in the morphology of the porous oxide structure.11 In particular, the process is believed to be responsible for the degeneration of the well-ordered porous morphology, typically observed on high purity aluminum, 12 into a globular or sponge-like morphology typically observed on copper containing alloys, 13,14 such as those of the 2xxx series 11,12 and 7xxx series.14 The morphology of the porous films on these alloys is of great technological interest, since anodizing is one of the most commonly applied corrosion-protection measures, 15 and anticorrosion performance and oxide morphology are closely related.16 As a consequence, the understanding of the interaction between the anodizing conditions, th...

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Investigations of burning phenomena during the hard anodising of aluminium by local in-operando temperature measurements

Cited by 27 publications

References 23 publications

Recent Advances in Nanoporous Anodic Alumina: Principles, Engineering, and Applications

Recent Advances in Nanoporous Anodic Alumina: Principles, Engineering, and Applications

Development of the local proton concentration during pulse anodizing

Gravimetric Measurement of Oxygen Evolution during Anodizing of Aluminum Alloys

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