Spectroscopic Characterization of Red Onion Skin Tannin and It’s use as Alternative Aluminium Corrosion Inhibitor in Hydrochloric Acid Solutions

Characterization of red onion skin tannin (ROST) was done using FTIR and UV/visible spectrophotometric techniques, revealing ROST to be made up of mixed (hydrolysable and condensed) tannins. ROST has been found to be an effective corrosion inhibitor of aluminium in hydrochloric acid solutions using gravimetric, thermometric, and UV/visible spectrophotometric techniques. Proposed kinetic model reveals complex reaction mechanism (parallel reactions) for aluminium corrosion inhibition by ROST. ROST adsorption on aluminium followed Langmuir isotherm in 0.1M and Fruendlich isotherm in 0.5M HCl and 2.0M HCl at 303 Kelvin. Physical adsorption (physisorption) of ROST on aluminium has been proposed.