The influence of neem leaf extract on corrosion inhibition of mild steel in 0.1 M HCl solution was studied using the weight loss method. Neem leaf extract which contains the double bond, carbonyl groups, and aromatic rings functional group as shown by the GCMS, phytochemical test, and FTIR analyses is one of the good natural plant extract that can be used as corrosion inhibitor. The weight loss on surface of mild steel at various inhibitor concentrations was determined. The highest inhibition efficiency of 93.24% was achieved using the neem leaf extract as corrosion inhibitor. Adsorption mechanism was investigated using Langmuir, Temkin, and Freundlich isotherms. Inhibitor adherence on the mild steel surface was spontaneous with the negative Gibb’s free energy value obtained. The mixed type adsorption mechanism (physisorption and chemisorption) is proposed for the inhibitor adsorption on mild steel surface. The inhibitor was adsorbed on the mild steel surface through adsorption of the phytochemical components on the surface of mild steel which protects the metal surface from corroding. The corrosion rate decreases from 0.001 to 0.0002MPY with increase in inhibitor concentrations and exposure time.
This study examined the corrosion inhibition of mild steel in 1.5M HCl solution using cocoa leaf extract as an inhibitor. The effect of inhibitor concentrations, kinetics, and time of immersion were undertaken at 30 o C while the thermodynamic parameters were determined with temperature range of 35 o C-55 o C. FTIR result indicated that the actual adsorption of the inhibitor is as a result of donation of single pair of electrons on oxygen to the vacant d-orbitals of the metal (mild steel) that leads to the formation of complexes on the mild steel surface. The corrosion rate decreased from 1.64 g/cm 2 hr to 0.09gm/cm 2 hr in the presence of inhibitor used. However, increased in temperature showed a decreased in inhibition efficiency this resulted to an increase in rate of corrosion. Half-life of the corrosion kinetics ranges from 49.71-53. 15hr which is directly proportional to the inhibitor concentrations. Activation energy Ea, enthalpy (∆H o), and entropy (∆S o) calculated showed good interactions. The enthalpy of activation ranges from 63.28kJ/mol to 97.55kJ/mol. Rise in activation energy with inhibitor concentration confirmed the physical (physisorption) adsorption mechanism for the corrosion of mild steel surface. Endothermic nature of the corrosion process is ascertained with the positive value of ∆H o obtained.
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