Electrical behaviour, characteristics and properties of anodic aluminium oxide films coloured by nickel electrodeposition

Porous anodic films on 1050 aluminium substrate were coloured by AC electrodeposition of nickel. Several experiments were performed at different deposition voltages and nickel concentrations in the electrolyte in order to correlate the applied electrical power to the electrical behaviour, as well as the characteristics and properties of the coatings. The content of nickel inside the coatings reached 1.67 g/m2, depending on the experimental conditions. According to the applied AC voltage in comparison with the threshold voltage Ut, the coating either acted only as a capacitor when U\Ut and, when U[Ut, the behaviour during the anodic and cathodic parts of the power sine wave was different. In particular, due to the semi-conducting characteristics of the barrier layer, additional oxidation of the aluminium substrate occurred during the anodic part of the electrical signal, whilst metal deposition (and solvent reduction) occurred during the cathodic part; these mechanisms correspond to the blocked and pass directions of the barrier layer/electrolyte junction, respectively

The use of the dye CI acid blue 45 in the electrolytic colouring of anodised aluminium

The electrolytic colouring of anodised aluminium from acidic tin(II) sulphate solutions in the presence of the dye Alizarin Saphirol B (Cl Acid Blue 45) has been investigated. The method combines electrolytic colouring and adsorptive dyeing in a single stage and expands the range of colours which can be produced by the electrolytic colouring process. A dye concentration in the acidic tin(II) sulphate colouring bath of 7.5 g/l and a treatment time of 1-2 min, at 15 V (50 Hz), results in a grey-blue hue with high fastness properties and resistance to corrosion. The mechanism of the action of the dye is discussed

The role of aluminum anodizing conditions on the effect of the additive light green

The influence of operating conditions such as temperature, concentration of electrolyte and applied voltage, on the effectiveness of the additive light green in a phosphoric acid bath, on film porosity and current density during anodizing of pure aluminum has been investigated using electrochemical methods. X-Ray fluorescence was used to determine the incorporated amount of phosphorous in the anodic oxide. The principal factor which affects the action of this additive seems to be the applied voltage, while the other parameters have a much smaller influence. © 2002 Elsevier Science B.V. All rights reserved

The influence of certain sulfonic triphenylmethane dyes, as additives, on anodizing of aluminum in phosphoric acid

The anions of the triphenylmethane sulfonic dye Light Green and its isomer Brilliant Blue added in the bath during anodization of pure aluminum (99.96%) in 0.4 M phosphoric acid under constant voltage, are concentrated at the bottom of the pores of the anodic coating and influence the anodic process. This influence was investigated using electrochemical methods, X-Ray Fluorescence (XRF) and Scanning Electron Microscopy (SEM). The observed decrease of anodizing current density can be explained by the fact that the Light Green anions adsorbed at the oxide/electrolyte interface inhibit the transfer of Al3+ ions to the electrolyte bulk. This results in a reduction of the field-assisted dissolution and of the direct ejection of Al3+ ions as well as of the rate of formation of anodic oxide at the metal/oxide interface. These events can be correlated with the observed decrease of porosity and population density of the pores in the presence of Light Green, which indicates an increase of the cells diameter. In addition, from the above experimental methods no alteration of the diameter of the pores and the barrier layer thickness seems to occur. The dye Brilliant Blue has a similar but much smaller influence. This can be explained by its structural differences. © 2001 Elsevier Science B.V. All rights reserved

The use of triaiylmethane dyes on aluminium

Coatings have been formed on the surface of unanodised aluminium electrolytically treated in an aqueous solution of tin sulphate and a triarylmethane dye. The coatings produced had a good decorative appearance, good adhesion and were 3-5 μm thick. The coloured films had excellent light fastness but poor resistance to corrosion resistance. The dyes showing the most promise for this appication were Cl Acid Blue 9 and Cl Acid Green 5. These dyes interfered in the current flow, in so doing modifying the surface topography and the semiconductive properties of the superficial aluminium oxide film formed during the colouring treatment. The dye fragmentation, cyclisation and dimerisation products derived during the electrolytic treatment resulted in the formation of organotin compounds

Acid-dyes as corrosion inhibitors for mechanically pretreated aluminum

Purpose - The purpose of this paper is to provide acid-dyes, known for the dyeing of porous aluminum oxide films, as inhibitors of the corrosion of aluminum in neutral chloride solutions. Design/methodology/approach - Potentiodynamic polarization plots are recorded on mechanically pretreated aluminum using a three-electrode cell containing 0.01 M NaCl solution with or without 0.025 mM of the acid-dyes monosulfonic methyl orange (MO), disulfonic chromotrop RR (CH), disulfonic alphazurine A (AZ) and trisulfonic light green SF yellowish (LG). The X-ray fluorescence technique is used in certain cases for the estimation of sulfur net content of the surface of the probes and thus of the concentration of the adsorbed dye. Findings - The inhibition efficiency of acid dyes on corrosion of mechanically pretreated aluminum seems to be related more to the presence of a following quinonoid structure which probably contributes more to the formation of mono- or bi-dentate compounds with the aluminum cations in the substrate than to the number of sulfonic groups in their molecule. Thus, the triphenylmethane dyes LG and, to a greater extent AZ, having this quinonoid structure means they are more efficient as corrosion inhibitors in near-neutral chloride solution than the azo dyes MO and CH, that do not have it. Practical implications - Selected acid-dyes such as triphenylmethane sulfonic-dyes, which have found wide application in the dyeing industry, seem to protect aluminum against the corrosive action of chlorides. Originality/value - This paper is intended to be the nucleus for the electrochemical studies of the effectiveness of acid dyes as corrosion inhibitors for aluminum. © Emerald Group Publishing Limited

Investigation of the relationship between the reflectance and the deposited nickel and tin amount on the aluminium anodic oxide film

Two distinct methods were used, energy dispersive X-ray fluorescence and specular reflectance measurement, in order to analyze the amount of the nickel and tin layers on anodic aluminium surfaces. These metals were electroplated at the bottom of the pores of anodized aluminium, during electrolytic colouring in solutions containing nickel borate and boric acid, tin sulphate and sulphuric acid, respectively. An exponential relation was derived giving the absorbance of each sample as a function of the surface density of the deposited metal. Various organic additives that improve the efficiency of the electrolytic procedure were used as well as AC or DC current which affects the situation of the anodic film; their influence on the calculated parameters was also investigated. © 1998 Elsevier Science S.A. All rights reserved

The influence of some triphenylmethane compounds on the corrosion inhibition of aluminium

Potentiostatic and potentiodynamic polarization, and scanning electron microscopy were used to investigate the effect of some basic and acid triphenylmethane derivatives, on the anodizing of pure aluminium in neutral ammonium borate electrolyte containing traces of chloride ions. The absence of sulfonic groups as substituents in these compounds restricts their action. The presence and position of sulfonic groups as substituents in their molecules influence the extent to which the molecular structures of these compounds approach coplanarity and their electronic configuration. As a result, a differentiation of their influence on the field assisted adsorption of chloride ions from solution on the hydrated oxide surface, and on the subsequent localized autocatalytic dissolution of the barrier oxide film by them is observed. © 2003 Elsevier Ltd. All rights reserved