Portugaliae Electrochimica Acta 2017, 35(5), 279-295 DOI: 10.4152/pea.201705279 PORTUGALIAE ELECTROCHIMICA ACTA ISSN 1647-1571 Corrosion Inhibition of Aluminium in Acidic Media by Different Extracts of Trigonellafoenum-graecum L Seeds A. Ennouri, * A. Lamiri and M. Essahli University Hassan 1, Faculty of Science and Techniques, Laboratory of Applied Chemistry and Environment, P.O. Box 577, Settat, Morocco Received October 16, 2016; accepted March 17, 2017 Abstract The corrosion inhibition of aluminum by the extract of Trigonellafoenum-graecum L was studied in a hydrochloric acid 1 M solution using electrochemical polarization measurements and electrochemical impedance spectroscopy (EIS). Three organic solvents, pentane, dichloromethane (DCM) and ethanol, of different polarities, were tested. An inhibition efficiency of 86.6 %, 84.41 %, and 75.77 % was obtained by the addition of 1400 ppm of the extract using three solvents: DCM, ethanol and pentane, respectively. The potentiodynamic curves show that the decrease of aluminum corrosion in the presence of the fenugreek extract in a HCl 1 M solution mainly acts by a mixed process with an anodic tendency for both extracts with ethanol and with pentane; on the other hand, the extract with DCM showed a cathodic tendency. The temperature effect on the corrosion of aluminum indicates that the inhibition efficiency of the natural substance decreases with an increase in temperature. The inhibition efficiency values obtained from the polarization curves are in good agreement with those of EIS. Keywords: aluminum, inhibition, corrosion, fenugreek, extract, solvent, hydrochloric acid. Introduction Corrosion is a natural phenomenon, which can be considered either chemical or electrochemical in nature, and it degrades the properties of metal and its alloys making them unusable. Aluminum is a soft, durable, lightweight, malleable metal with appearance ranging from silvery to dull gray, depending on the surface roughness and is nonmagnetic and non-sparkling. Aluminum and its alloys are recommended for building purposes and for various internal outfits, at various industries and highly polluted places. Aluminum is remarkable for its low density and ability to resist to corrosion to some extent, due to the phenomenon of passivation, but its corrosion always takes place in aqueous acidic conditions. * Corresponding author. E-mail address: amal.ennouri@gmail.com