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The growth kinetics and properties of potentiodynamically formed thin oxide films on Al were investigated in 0.05 M citric acid solutions of different pH (5, 6 and 7) by means of potentiodynamic polarization and a.c. electrochemical impedance spectroscopy (EIS) measurements. Al showed passive behaviour within the pH range that was examined. The potentiodynamic growth of the oxide film on Al takes place due to ionic conductivity under the influence of the high electric field. Characteristic kinetic oxide film growth parameters such as the high-field growth exponential law constants (A and B), ionic conductivity through the oxide film, field strength and half barrier width have been calculated. Impedance measurements were used to determine the parameters related to the characteristic sizes and properties of oxide film. The capacitive response of the impedance spectrum was related to the thickness and dielectric properties of the barrier oxide film. The oxide film resistance values were very high, indicating that the oxide films formed under potentiodynamic conditions are highly uniform in thickness and very resistant. The anodic behaviour of Al in the citric solutions under potentiodynamic conditions were characterized by the rapid growth of the oxide film which diminished the influence of relaxation processes on the growth kinetics and structural characteristics of the aluminium/anodic oxide film/electrolyte system.

The electrochemical and surface properties of aluminium in 0.05 M citric acid solutions of pH 2–8 were studied by means of open circuit potential (OCP), potentiodynamic polarization and potentiostatic current–time transient measurements. The OCP reached a steady-state value very slowly, probably due to the slow rate of detachment of surface complexes into the solution. Aluminium exhibits passive behaviour in citric acid solutions of pH 4–8. Tafel slopes b c were characteristic for hydrogen evolution on aluminium covered by an oxide film. The corrosion kinetic parameters E corr, i corr and b a suggest that surface processes are involved in the dissolution kinetics, especially in the pH range 3–6. Current–time transient measurements confirm that, in citric acid solutions of pH 3–6, the dissolution is controlled by surface processes, that is, by the rate of detachment of surface complexes, while in solutions of pH 2, 7 and 8 dissolution is under mass-transport control. The addition of fluoride ions to citric acid changes the controlling steps of the dissolution process. Citrate and fluoride ions compete for adsorption sites at the oxide surface, and adsorption of these ions is a competitive and reversible adsorption.

Aluminium levels in human milk in the winter period of 1992./93. ranged from 0.004 mg/l to 2.67 mg/l and the mean value was 0.38 mg/l. The nursing women were divided into several groups according to the results of a questionnaire, i.e. according to their social status (if they were refugees or not), number of deliveries, post partum day, the weight they put on during pregnancy, their age, and smoking habits. The mean levels of aluminium for each group were presented. The measurement of aluminium was done by graphite furnace atomic absorption spectrophotometry.

The corrosion of aluminium (Al) in several brands of soft drinks (cola- and citrate-based drinks) has been studied, using an electrochemical method, namely potentiodynamic polarization. The results show that the corrosion of Al in soft drinks is a very slow, time-dependent and complex process, strongly influenced by the passivation, complexation and adsorption processes. The corrosion of Al in these drinks occurs principally due to the presence of acids: citric acid in citrate-based drinks and orthophosphoric acid in cola-based drinks. The corrosion rate of Al rose with an increase in the acidity of soft drinks, i.e. with increase of the content of total acids. The corrosion rates are much higher in the cola- based drinks than those in citrate-based drinks, due to the facts that: (1) orthophosphoric acid is more corrosive to Al than is citric acid, (2) a quite different passive oxide layer (with different properties) is formed on Al, depending on whether the drink is cola or citrate based. The method of potentiodynamic polarization was shown as being very suitable for the study of corrosion of Al in soft drinks, especially if it is combined with some non-electrochemical method, e.g. graphite furnace atomic absorption spectrometry (GFAAS).