Naslov
Impedance and transient study of aluminium in citric acid solutions

Autori
Šeruga, Marijan ; Hasenay, Damir

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
51st Annual ISE Meeting - Abstracts / - Varšava : International Society of Electrochemistry, 2000

Skup
51st Annual ISE Meeting

Mjesto i datum
Varšava, Poljska, 03.09.2000. - 08.09.2000

Vrsta sudjelovanja
Poster

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
Aluminium; Citric acid; Oxide film; Chronoamperometry; Electrochemical impedance spectroscopy

Sažetak
The electrochemical properties of the high purity aluminium (Al 99.999%) in 0.05 M citric acid solutions of different pH values (4-8) were studied, by the means of chronoamperometry and electrochemical impedance spectroscopy (EIS) techniques. An EG&G PAR Model 273A Potentiostat and EG&G PAR Lock-In Amplifier Model 5210, controlled by PC, were used in electrochemical measurements. The effect of the pH values of citric acid solutions and the passivation potential on the properties and the growth kinetics of the passive film formed on aluminium have been examined. The results show that the combination of the chronoamperometry and EIS measurements can be successfully applied in the analysis of passive behaviour of aluminium electrode, especially as it makes it possible to distinguish the elementary processes taking place at the electrode during anodic polarization, and to determine the actual thickness of the barrier film. In citric acid solutions aluminium exhibits passive behaviour, due to formation of thin high protective barrier-type passive film. The steady state thickness of the barrier film was shown to increase linearly with applied passivation potential, while solution pH has no significantly influence on the thickness of the film. In anodic passivation at a constant potential, the characteristic decay of anodic curent with time was observed. The process of formation of barrier film on aluminium takes place with considerable current loss. Analysis of the impedance diagrams has shown that impedance of the system Al/barrier film/citric acid solution is characterized by a high-frequency capacitive and a low-frequency inductive behaviour. The high-frequency capacitive behaviour can be related to the thickness and dielectric properties of the barrier oxide film. The observed low-frequency inductive loop of the impedance spectra can probably be attributed to the relaxation processes at the film/solution interface, e.g. to the relaxation effect of the adsorption-desorption processes at the aluminium oxide/citric acid solution interface. The mechanism of barrier film growth on aluminium in citric acid solutions has been examined within the framework of various models for passive film growth. It seems that the observed results best correlate with the models which considers the defect character of the oxide film, i.e. with the point defect model proposed by Macdonald and the MacDougall’s defect model for the growth kinetics of the oxide film.

Izvorni jezik
Engleski

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