PHYTOCHEMICAL AND THERMODYNAMIC STUDIES OF PAWPAW LEAF (ASIMINA TRILOLA) EXTRACT AS CORROSION INHIBITOR OF ZINC IN KOH MEDIUM
This work presents a report of phytochemical and thermodynamic studies of pawpaw leaf extract as a corrosion inhibitor of zinc in 1M KOH. The extract was subjected to qualitative and quantitative phytochemical analyses. Applying the thermometric technique, reaction numbers for the zinc dissolution in free and inhibited KOH media were used to determine the inhibition efficiency of the extract. The gravimetric method was carried out using one-factor at a time coupled with response-surface methodology. Central Composite Design of Design Expert Software was employed in the optimization process. Analyses of the results revealed that the pawpaw extract is predominantly made up of flavonoids (365.0 mg/100g) and tannins (270.0 mg/g). The degree of surface coverage of the zinc increased with increase in inhibitor concentration, but decreased with increase in temperature. The adsorption of the extract on the zinc surface appears to obey the mechanism of physical adsorption, as it is best fitted by Langmuir adsorption isotherm. A quadratic model adequately described the relationship between the inhibition efficiency and the factors of concentration, temperature and time. The highest inhibition efficiency of 86.6% was obtained at inhibitor concentration of 1.0 g/l, temperature of 303 K and immersion time of 5 hours. The pawpaw leaf extract is therefore a suitable inhibitor for corrosion inhibition of zinc in KOH medium.