a Sodium silicate solutions are widely used chemicals for a variety of applications. In particular, they are commonly used in pre-treatments of aluminium alloys as cleaners and corrosion inhibitors. Another application is found in offset printing, where after graining and anodising, a silicate-based post-anodic treatment (PAT) is considered to optimise the aluminium plate characteristics. It is, however, not clear what type of interaction takes place between the oxide-covered aluminium and the silicate solution. In this work, silicate-based PAT is studied. Different barrier-type and porous-type aluminium oxides are silicate-treated by dipping in a water-based sodium silicate solution and the effect of time on the deposition is studied. Particular attention is given to the role of rinsing when the alumina surface is washed in water after the silicate treatment. A good understanding of the role of rinsing allows us to obtain information on the characteristics of the silicate layer which is formed after dipping. The surface modifications induced by the silicate treatment on the aluminium oxides were monitored by means of field emission scanning electron microscopy and infrared spectroscopic ellipsometry. Quantitative measurements on the amount of deposited silicate were taken by X-ray fluorescence, and relative comparisons between different oxides are shown. Auger electron spectroscopy was used to study the in-depth composition of the silicate deposition. Experiments show a high affinity of the silicate to the anodic oxide film. A thin nanometric chemisorbed (alumino)silicate layer is present on the surface after rinsing, while the physisorbed part of the layer is washed away.

Sodium silicate solutions, also known as 'water-glass', are used for a wide variety of applications. In particular, they are commonly used in pre-treatments of aluminum alloys as cleaners and corrosion inhibitors. Silicate films are known to be promising for corrosion protection and to confer high hydrophilicity. One of the main issues in the study of the formation of silicate films on metal oxides is the complexity of the anionic speciation in aqueous solution. In this work, the mechanism of sodium silicate interaction with porous anodic alumina and its dependence on the solution characteristics is studied by means of Fourier transformed infrared spectroscopy (FTIR). Grazing angle-FTIR and attenuated total reflection-FTIR are used in order to monitor the chemical changes occurring with time on the surface upon silicate adsorption. The effect of the SiO 2 /Na 2 O molar ratio and the temperature is studied. The role of rinsing is investigated when the alumina surface is washed in water after the silicate treatment. A chemical description of the phenomena occurring during silicate treatment is given.

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The anodizing of aluminium is an electrochemical surface treatment yielding the formation of an alumina film, the characteristics of the formed oxide strongly depending on the considered anodizing conditions. Heat transfer has an important influence on the anodizing process, which can be explained by considering the production of heat near the aluminium anode, combined with the significant influence of the local electrode temperature on the process of oxide formation. The influences of temperature and heat transfer on the growth of the anodic oxide film during anodizing of high purity Al are studied on a laboratory scale in a wall-jet electrode reactor. The impinging jet configuration of the reactor creates a non-uniformly accessible electrode with variable convection as a function of the radial position on the anode. The influence of the resulting non-uniform heat transfer on the local temperature of the electrode is monitored by local temperature measurements on the backside of the aluminium anode, whereas its influence on local film growth is evaluated by means of FEG-SEM surface and cross sectional analyses. A comparison between the simulated and experimentally acquired data is presented. The controlled and known electrolyte flow in the wall-jet reactor enable numerical simulations of the convection which supply additional information on the encountered conditions of heat transfer. The anodizing process itself is simulated using a model based on the high field theory.