Pilling–Bedworth ratio of thick anodic aluminium porous films prepared at high voltages in H2SO4 based electrolyte

Thick porous anodic films have been prepared using high voltages in a sulphuric acid based electrolyte. The use of H2SO4 low concentration, low bath temperature and the boric acid as modifier allows the anodic porous film to be significantly thickened preventing its chemical dissolution. A new relation including the Pilling–Bedworth ratio, especially of the thick anodic porous films, is proposed here to take into account the nanoporosity and the anodic current efficiency

Influence of the anion specificity on the anodic polarization of titanium

The anodic polarization of titanium in the presence of selected electrolytes at 0.1 mol/L concentration has been investigated. The results were interpreted according to the categorization of anions based on their cosmotrope/chaotrope character. The aggressiveness of the anions is found to be related for a part to their proneness to loose their hydration shell during the penetration of the passive film, provided they can access sufficiently to the passive surface

Chemical behavior of tungstate solutions. Part 1. A spectroscopic survey of the species involved

This study is focused on the composition and the evolution of tungstate ions solutions as a function of pH and increasing concentrations. The Raman analysis showed that, during the titration of the tungstate solutions, WO4 2−, HWO4 − ions and probably W2O7 2−, HW2O7 2− and H2W2O7 solvated species could exist in aqueous solutions. For diluted solutions, additions of a strong acid does not cause any precipitation, whereas the formation of the unstable solid tungstic acid (H2WO4 or WO3·H2O) could occur in concentrated solutions

Chemical analysis of a single basic cell of porous anodic aluminium oxide templates

We prepared anodic aluminium oxide (AAO) templates with “honeycomb” geometry, i.e. hexagonally ordered circular pores. The structures were extensively studied and characterized by EPMA coupled with FEG-SEM and FEG-TEM coupled with EDX at meso and nanoscopic scales, in other words, at the scale of a single basic cell making up the highly ordered porous anodic film. The analyses allowed the identification of the chemical compounds present and the evaluation of their levels in the different parts of each cell. Of note was the absence of phosphates inside the “skeleton” and their high content in the “internal part”. Various models of porous anodic film growth are discussed on the basis of the results, contributing to a better understanding of AAO template preparation and selfnanostructuring phenomena

Influence of the anion specificity on the electrochemical corrosion of anodized aluminum substrates

The electrochemical corrosion of anodized aluminum substrates in the presence of various electrolyte solutions at 0.01 mol L−1 concentration has been investigated. The comparative results were found to exhibit a correlation between the aggressiveness of the anions and their cosmotrope/chaotrope nature. The origin of the observed behavior was assumed to result from a variable resistance against dehydration during the pitting process

Impact of the type of anodic film formed and deposition time on the characteristics of porous anodic aluminium oxide films containing Ni metal

Porous anodic films containing nickel were prepared by AC electro-deposition. The porosity of the films was controlled by using different working conditions (anodisation electrolyte, voltage, and time). Then nickel was electro-deposited using an alternating voltage. The impact of the anodic film on the current density waveforms and the metal content can largely be explained by the porosity differences, while changing the deposition time caused changes due to over-oxidation of the aluminium substrate, experimentally proved by TEM. Finally, the impact of deposition time on the deposited metal was successfully fitted using an Elovich type law over a large time-span (up to 1800 s), showing the ability to achieve precise control of the metal content

Black anodic coatings for space applications: study of the process parameters, characteristics and mechanical properties

Black inorganic anodized aluminium alloys are used for managing passive thermal control on spacecraft and for avoiding stray light in optical equipment. Spalling of these coatings has sometimes been observed after thermal cycling on 2XXX and 7XXX aluminium alloys. This phenomenon could generate particulate contamination in satellites and may affect mission lifetime. In this work, the influences of the four main steps of the process (pretreatments, sulphuric anodizing, colouring and sealing) on the coating characteristics have been studied for a 7175 T7351 aluminium alloy. The chemical heterogeneity of the coating has been underlined, and its mechanical behaviour observed through crazing. Scratch-testing, used to evaluate coating adhesion to its substrate, revealed the negative impact of thermal cycling

Improvement of the tribological behavior of PTFE-anodic film composites prepared on 1050 aluminum substrate

A model anodic film was prepared to incorporate PolyTetraFluoroEthylene (PTFE) nanoparticles into the porous structure of the film. Firstly, the influence of the anodization parameters on the morphology (thickness and pore diameter) was studied, using notably FEG scanning electronic microscopy. Then, using an improved sedimentation technique, the nanoparticles were successfully inserted into the porous structure and onto its surface. EDX and Raman spectroscopy attested the presence of PTFE particles down to the bottom of the pores. Secondly, the study demonstrated the benefit of incorporating the PTFE particles. Tribological tests were also carried out and the lubricating properties of the composite analyzed. Friction coefficient curves showed a 75 fold improvement of the total lifetime of the anodic film with a reduced friction coefficient

L'électrochimie pour la décoration et la création artistique : Coloration de l'aluminium en architecture et en aluchromie

Au cours de la création d'une œuvre artistique sur substrat métallique, l'électrochimie intervient essentiellement au niveau des traitements de surface. La surface métallique peut être par exemple modifiée par électropolissage ou par brillantage électrolytique afin d'obtenir une grande brillance, puis par anodisation menant alors suivant les conditions opératoires à un film anodique soit compact soit poreux. Les films compacts sont mis en oeuvre avec succès sur plusieurs métaux (Al, Ti, Nb), la coloration résultant alors de phénomènes interférentiels. Le second cas concerne les films anodiques poreux, obtenus usuellement sur les substrats d'aluminium. L'existence de cette porosité permet d'intégrer des colorants ou des pigments organiques, minéraux ou métalliques. Depuis les années 1960, le procédé de coloration électrolytique permet ainsi de déposer du métal au fond des pores, et par là même de décorer des éléments métalliques en architecture. Pour sa part, le mouvement artistique des Aluchromistes a plutôt mis en oeuvre la coloration chimique organique, qui permet une plus grande variété de coloris et de nuances, ainsi qu'une plus grande facilité d'élaboration de motifs et de formes

Surface integrity after pickling and anodization of Ti–6Al–4V titanium alloy

The surface integrity of Ti–6Al–4V titanium alloy was studied at different stages of surface treatments, especially pickling and compact anodization, through surface characteristics potentially worsening fatigue resistance. No significant changes of the equiaxe microstructure were detected between sample core and surface, or after the pickling and anodization steps. Surface hydrogen and oxygen superficial contents were found to remain unchanged. Roughness characteristics (i.e. Ra, Rz but also local Kt factor) similarly showed only slight modifications, although SPM and SEM revealed certain random local surface defaults, i.e. pits about 400 nm in depth. Finally internal stresses, evaluated using X-ray diffraction, highlighted a significant decrease of the compressive internal stresses, potentially detrimental for fatigue resistance