Faculty of Pharmacy, University of Tuzla and Faculty of Food Technology, University of J. J. Strossmayer Osijek
Abstract
Caffeine (1,3,7-trimethylxanthine) was isolated from black tea and characterised using different physical methods. The corrosion inhibition performance of the caffeine isolate (in concentration from 110-5 to 110-3 mol/dm3) on aluminium alloy corrosion in neutral 0.5 mol/dm3 NaCl solution was investigated using potentiodynamic and linear polarization measurements at 20 C. Corrosion potential, corrosion current and polarization resistance were determined and surface coverage of inhibitor molecules and inhibition efficiency were calculated. The obtained results show that caffeine effectively inhibited the corrosion reaction in the chloride solution with an inhibition efficiency of up to 76%. Furthermore, caffeine was found to function essentially as a mixed type with a higher influence on cathodic reaction. The adsorption behaviour of investigated inhibitor can be described by the Freundlich adsorption isotherm. The adsorption free energy closes to -10 kJ/mol indicates physical adsorption of the caffeine on the aluminium alloy surface in NaCl solution
