Ong C., Karim K., 2017, Inhibitory Effect of Red Onion Skin Extract on the Corrosion of Mild Steel in Acidic Medium, Chemical Engineering Transactions, 56, 913-918.
The inhibition efficiency of methanol extract of red onion peel on the corrosion of mild steel in hydrochloric acid (HCl) solution has been investigated through weight loss measurements. This study was conducted by immersing mild steel coupon into 1.0 M of HCl solution without and with the presence of red onion peel extracts (ROPE) (0.5 – 2.0 g/L) and at various temperatures (303 to 333 K) for 7 d. Fourier Transform Infrared (FT-IR) spectroscopy analysis indicated that the inhibition of mild steel corrosion was mainly contributed by C- O and aromatics compounds. These compounds were adsorbed on the mild steel surface and formed a thin layer of protective barrier. From the weight loss measurement, the inhibition efficiency of 90 % was obtained in the HCl solution containing 2.0 g/L of ROPE at temperature of 303 K. The inhibition efficiency was found to increase with increasing inhibitor concentration but decrease with increasing temperature of acid solution. This is because mild steel is oxidised at a higher rate at high temperature which causes the ROPE to desorb from the surface of mild steel. The adsorption mechanism of ROPE on the mild steel obeys the Langmuir adsorption isotherm within the range of temperature studied.
