Corrosion Inhibition of Mild Steel in Hydrochloric Acid by Tannins Rom Rhizophora Racemosa
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Abstract
Studies on the corrosion behaviour of mild steel electrodes in inhibited hydrochloric acid are described. Conventional weight loss measurements show that a maximum concentration of 140 ppm of tannin from Rhizophora racemosa is required to achieve 72% corrosion inhibition. Similar concentration of tannin: H<sub>3</sub>PO<sub>4</sub> in ratio 1:1 gave 61% inhibition efficiency, whereas efficiency obtained for phosphoric acid as inhibitor in the same environment was 55%. Corrosion rates obtained over six hours of exposure in 1M HCl solution at inhibitor concentrations of 140 ppm are 2 mA/cm<sup>2</sup>, 2.4 mA/cm<sup>2</sup>, 2.6 mA/cm<sup>2</sup> and 6 mA/cm<sup>2</sup> for tannin, tannin/H<sub>3</sub>PO<sub>4</sub> and H<sub>3</sub>PO<sub>4</sub>-inhibited and uninhibited specimens respectively. Natural atmospheric exposure studies revealed that specimens treated in H<sub>3</sub>PO<sub>4</sub> resisted corrosion for three weeks, while tannin treated specimens suffered corrosion attack after one week of exposure tests.
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