The inhibition efficiency of an aqueous extract of garlic in controlling corrosion of aluminium immersed in sodium hydroxide solution at pH 11 and 12, in the absence and presence of Zn2+, was evaluated by the weight loss method. At pH 11, the extract accelerated corrosion of aluminium in the absence and presence of Zn2+. The influences of N-cetyl-N,N,N-trimethylammonium bromide (CATB) (a biocide and a cationic surfactant) and immersion period on the inhibition efficiency were investigated. The influence of sodium sulphite, an oxygen scavenger, on the inhibition efficiency of the inhibitor system revealed that transport of inhibitor towards the metal surface plays a greater role than the removal of oxygen from the aqueous solution in determining the inhibition efficiency of the system. The protective film was analysed with the use of Fourier transform infrared spectra.
