AC-impedance measurements on porous aluminium oxide films

Hitzig, J.; Jüttner, K.; Lorenz, W.J.; Paatsch, W.

doi:10.1016/0010-938x(84)90115-x

Cited by 165 publications

(94 citation statements)

References 18 publications

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“…5). Since Hoar and Wood, 26 various equivalent circuits have been proposed to model the EIS response of porous anodic films, particularly the equivalent circuit proposed by Hitzing et al, 27 which is presented in Figure 5a. In this model, R s represents the solution resistance, R w and CPE w represent resistance and capacitance associated to the pore walls, R bl and CPE bl represent the capacitance and resistance due to the presence of the barrier layer, and R seal and CPE seal represent the capacitance and resistance associated to the presence of sealing products within the pores.…”

Section: Resultsmentioning

confidence: 99%

Application of EIS to In Situ Characterization of Hydrothermal Sealing of Anodized Aluminum Alloys: Comparison between Hexavalent Chromium-Based Sealing, Hot Water Sealing and Cerium-Based Sealing

Carangelo

Curioni

Acquesta

et al. 2016

J. Electrochem. Soc.

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Chromic acid anodizing has been used for almost a century to enhance corrosion protection of aerospace alloys. For some applications, hydrothermal sealing in hexavalent chromium-containing solution is required to enhance further the corrosion resistance but, due to environmental concerns, the use of hexavalent chromium must be discontinued. Good progress has been made to replace chromates during anodizing but comparatively less effort has focused on the sealing process. In this work, for the first time, electrochemical impedance spectroscopy (EIS) has been used to characterize in-situ the sealing processes occurring during hot water sealing, sodium chromate sealing and cerium sealing. The results suggest that the processes occurring during sodium chromate sealing are significantly different compared to hot water and cerium sealing. In particular, during chromate sealing, the porous skeleton is significantly attacked, suggesting that the anticorrosion performance is likely to arise from the residuals of chromate rather than from the improvement of the barrier properties. In contrast, during hot water sealing, little attack occurs on the porous skeleton, and the improved corrosion protection is due to the enhanced barrier effect. During cerium sealing, precipitation of cerium products occurs, providing an inhibitor reservoir, and little, if any, attack occurs on the pre-existing oxide. Chromic acid anodizing (CAA) is widely used in the aeronautic industry to improve corrosion resistance of aluminum alloys.1 Since the beginning of the 1990s, however, the high toxicity associated with Cr (VI) has imposed restrictions on their use in industrial applications. As a consequence, numerous attempts have been made to find less toxic alternatives. 2,3Anodizing with dilute sulfuric acid (DSA) has been used to obtain thin anodic films (1-5 μm) that provide some protection without excessive deterioration of the fatigue life for specific aerospace alloys. Although the fatigue performance of DSA is acceptable, the corrosion resistance is lower than that of parts anodized in chromic acid (CAA). More recently, a new anodizing procedure, involving the addition of tartaric acid in dilute sulfuric acid electrolyte and called tartaric-sulfuric acid anodizing (TSA), was introduced.4-6 The addition of tartaric acid to sulfuric acid baths improves significantly the anticorrosive properties of the anodic layers compared to those obtained by sulfuric acid anodizing.7 Recent work, 7 however, indicates that the mechanism of porous film growth is not significantly affected by tartaric acid additions and that tartaric acid is not incorporated in significant amounts into the oxide material. Thus the corrosion resistance provided by TSA is likely to be associated with residuals of tartaric acid adsorbed on the porous skeleton. Tartaric acid concentration in the order of ppm, has been proved to be effective in reducing both the oxide dissolution rate in acidic environments and the anodic reaction rate. The effect of tartaric acid on the anodic fi...

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Section: Resultsmentioning

confidence: 99%

Application of EIS to In Situ Characterization of Hydrothermal Sealing of Anodized Aluminum Alloys: Comparison between Hexavalent Chromium-Based Sealing, Hot Water Sealing and Cerium-Based Sealing

Carangelo

Curioni

Acquesta

et al. 2016

J. Electrochem. Soc.

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“…These transformations cause a progressive increase in R p , reflected by a shift of the central section in the Bode diagrams towards higher Z values (Fig. 9, Tables 7 and 8), which, according to the literature, is equivalent to a progressive improvement in anodic film quality [21,22,30]. This type of behaviour, verified in a wide variety of atmospheres for pure Al anodic films [17,24], is thus repeated with Al-Mg and Al-Si-Mg, which present entirely comparable ageing processes.…”

Section: Anodic Film Ageing Processmentioning

confidence: 99%

“…This figure also shows in schematic form how the capacitance of the barrier and porous layers, C b and C p , can be estimated by extrapolation of the straight line regions to the angular frequency ω = 1, and how the porous layer resistance, R p , can be estimated from the impedance value corresponding to the minimum phase angle θ [13]. Different equivalent circuits have been proposed to simulate the behaviour of anodised aluminium [13,[29][30][31]. The very simple circuits initially proposed by Hitzing and Juttner for sealed and unsealed anodic films and reproduced in Fig.…”

Section: Characterisation Of Anodic Layers By Eismentioning

confidence: 99%

Behaviour of different bare and anodised aluminium alloys in the atmosphere

Bartolomé

Río²,

Escudero

et al. 2008

Surface and Coatings Technology

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Exposure tests in natural atmospheres are an indispensable means for determining the behaviour and durability of metallic materials in the atmosphere. The corrosion behaviour of bare aluminium and anodised aluminium with three different coating thicknesses has been evaluated for two years' exposure in two natural atmospheres of very different corrosivities: one urban and the other marine. Several techniques have been used to evaluate changes in the specimens during exposure, but special attention is paid to the direct measurement of corrosion by gravimetry and its indirect estimation by the comparatively much more sensitive electrochemical impedance spectroscopy (EIS) technique. The results show that if no demands are placed on the conservation of its appearance, aluminium may be used without protection even in atmospheres of medium or high corrosivity. The anodising and sealing of aluminium alloys, above an ill-defined minimum thickness threshold, is an appropriate solution to prevent localised corrosion of aluminium and to conserve its appearance, even in aggressive atmospheres.

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“…La aplicación de la espectroscopia de impedancia electroquímica (EIE), para establecer la resistencia a la corrosión del óxido obtenido por anodizado del aluminio ha sido usada ampliamente [12,15]. Las cualidades de las denominadas capa porosa y capa barrera que componen el óxido de aluminio obtenido por anodizado y caracterizadas por los valores de R po , C po y R b , C b , respectivamente, puede ser obtenidos por circuitos eléctricos equivalentes que simulan la data de impedancia del óxido protector.…”

Section: Introductionunclassified