The inhibitive action of the mucilage extracted from the modified stems of prickly pears,
toward acid corrosion of aluminum, is tested using weight loss, thermometry, hydrogen
evolution and polarization techniques. It was found that the extract acts as a good corrosion
inhibitor for aluminum corrosion in 2.0 M HCl solution. The inhibition action of the extract
was discussed in view of Langmuir adsorption isotherm. It was found that the adsorption of
the extract on aluminum surface is a spontaneous process. The inhibition efficiency (IE) increases
as the extract concentration is increased. The effect of temperature on the IE was
studied. It was found that the presence of extract increases the activation energy of the corrosion
reaction. Moreover, the thermodynamic parameters of the adsorption process were
calculated. It was found also that the Opuntia extract provides a good protection to aluminum
against pitting corrosion in chloride ion containing solutions.