Abstract
One of the most effective ways of mitigating the corrosion of metals in various media is by using of corrosion inhibitors. Due to the harmful effects of chemical-based corrosion inhibitors, attention is now shifting to plant materials which are environmentally friendly. Therefore, this paper investigates the corrosion inhibition potentials of Ficus exasperata and Costus afer leaves extracts on the corrosion of mild steel in 0.5 M hydrochloric acid medium at different temperatures (303 – 343 K). Secondly, to determine the effect of temperature on the corrosion inhibition performance of Ficus exasperata and Costus afer. The weight loss method of corrosion measurement was used to evaluate the corrosion inhibition potentials of the plant extracts. The results showed that Ficus exasperata and Costus afer inhibited the corrosion of mild steel in hydrochloric acid medium at all temperatures. Corrosion rates decreased with increase in concentration of the extracts. Concentration of the extracts used (0.125 g/L, 0.25 g/L, 0.5 g/L, 1.25 g/L and 2.5 g/L) did not significantly (p > 0.05) affect the corrosion rate of mild steel in the acidic media. Corrosion rates increased with increase in temperature. Inhibition efficiencies of the extracts increased with increase in concentration of the extracts and decreased with increasing temperatures. The adsorption of the extracts on the metal surface occurred by physical adsorption. Ficus exasperata and Costus afer could serve as effective inhibitors for mild steel in acidic media and their efficiencies are affected by high temperatures

Key words: Corrosion rate, Inhibition efficiency, Temperature, Ficus exasperata, Costus afer