The inhibition efficiency (IE) of an aqueous extract of beet root (BR) in controlling corrosion of carbon steel in well water in the absence and presence of Zn 2+ has been evaluated by mass loss method. The formulation consisting of 4 mL of BR extract and 50 ppm Zn 2+ offers 98% inhibition efficiency to carbon steel immersed in well water. A synergistic effect exists between BR extract and Zn 2+ . Addition of N-Cetyl-N,N,Ntrimethylammonium bromide (CTAB) does not change the excellent inhibition efficiency of the BR -Zn 2+ system. The BR -Zn 2+ system shows excellent IE up to 7 days. Polarization study reveals that this formulation controls the cathodic reaction predominantly. AC impedance spectra reveal that a protective film is formed on the metal surface. FTIR spectra reveal that the protective film consists of Fe 2+ -betanin complex and Zn(OH) 2 . The film is found to be UV -fluorescent.

The inhibition efficiency (IE) of an aqueous extract of Hibiscus rosa-sinensis (white) in controlling corrosion of aluminium at pH 12 has been evaluated by weight loss method in the absence and presence of Zn 2+ . The formulation consisting of 8 mL flower extract (FE) and 50 ppm of Zn 2+ had 98% inhibition efficiency. Polarization study revealed that this formulation functioned as cathodic inhibitor. AC impedance spectra revealed the presence of a protective film formed on the metal surface. FTIR spectra revealed that the protective film consisted of a complex formed between the active principle of the flower extract and Al 3+ .

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