CORROSION OF ALUMINUM IN SOFT DRINKS

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 th e corrosion of Al in soft drinks is a very slow, time-dependent and co mplex process, strongly influenced by the passivation, complexation an d adsorption processes. The corrosion of Al in these drinks occurs pri ncipally due to the presence of acids: citric acid in citrate-based dr inks 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 h igher in the cola-based drinks than those in citrate-based drinks, due to the facts that: (1) orthophosphoric acid is more corrosive to Al t han is citric acid, (2) a quite different passive oxide layer (with di fferent 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 nonelectrochemical met hod, e.g. graphite furnace atomic absorption spectrometry (GFAAS).