Studies on the inhibition of mild steel corrosion by some plant extracts in acidic medium

Carica papaya and Azadirachta indica leaves extracts were separately used as inhibitor for the corrosion of mild steel with chemical composition: 0.05%S, 0.023%S and 0.004%C, in 0.5M H2SO4 at 30 degrees C and 40 degrees C. The percentage inhibition efficiency was found to increase with increase in concentration of both inhibitors. For carica papaya, the % inhibition efficiency varied from 72.8% to 87.5% at concentration of 2.50x10(-4) to 1.25x10(-3) gdm(-3) at 30 degrees C and for Azadirachta indica, 60.31% to 75.75% at similar concentration range. Increase in temperature lowered inhibition efficiency of both inhibitors, although the effect of concentration of inhibitor was same as at lower temperature. The maximum % inhibitor efficiency was obtained at 30 degrees C. Carica papaya (87.5% at 1.25 x 10(-5) gdm(-3)) is a better inihibitor than Azadirachta indica (75.95% at 1.25 x 10(-3) gdm(3)). Analysis of the weight loss results gave a first order type mechanism. The average energies of activation (Ea) for corrosion of the mild steel in 0.5 M H2SO4 with carica papaya and Azadirachta indica were found to be 51.80 KJ mol(-1) and 53.63 KJ mol(-1) respectively Evidence is hereby provided to show that the plant extracts like some other organic compounds are good pickling inhibitors. (Nigeria) plant extracts. An example is the study carried out by Igwe and Okafor (1989). In view of the expanding research into possible corrosion inhibitors, the present study deals with the corrosion of mild steel in H2SO4. The inhibitive effect of Carica papaya (paw paw) and Azadirachta indica (neem) leaves extract on the corrosion rate of mild steel in 0.5 M H2SO4 has been studied using weight loss technique. The effect of temperature on the inhibiting action is also reported.