Abstract:
The investigation of the corrosion inhibition of X60 steel and 2017A aluminium in 1 M
hydrochloric acid medium by aqueous (EA) and ethanolic (EE) extracts of Nigella sativa L.
seeds, Punica granatum fruit peel and Pelargonium graveolens leaves, was performed using
electrochemical techniques, High Performance Liquid Chromatography (HPLC), Fourier
Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM).
The results of the study showed that the inhibition efficiency E (%) increases with increasing
extract concentration and decreases with temperature rise. The study of the influence of
temperature allowed us to understand the mechanism of action of these inhibitors on the
corrosion of steel and aluminium. We found that the actives molecules of the studied extracts
adsorb on the metal surface by forming physical bonds following the Langmuir adsorption
isotherm. These extracts behave as mixed type inhibitors, with a cathodic predominance in the
case of aluminium in the presence of EA and EE extracts of Nigella sativa L seeds.
The ethanolic extract of Nigella sativa L. seeds exhibit the best inhibition efficiency (96.7%)
on steel with 4g/L, while Punica granatum fruit peel provides maximum efficiency (78.9%)
with aluminium for 7g/L of the ethanolic extract. The leaves of Pelargonium graveolens are
more efficient with aluminium and give an inhibition efficiency of 88.6% for 1g/L of
ethanolic extract and 5g/L of aqueous extract.
