EXPERIMENTAL AND COMPUTATIONAL STUDIES OF CORROSION IN HIBITION POTENTIAL OF SELECTED PLANT EXTRACTS ON CORROSION OF MILD STEEL AND ALUMINIUM IN ACID MEDIUM

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dc.contributor.authorAWE, FEMI EMMANUEL
dc.date.accessioned2016-07-15T09:36:05Z
dc.date.available2016-07-15T09:36:05Z
dc.date.issued2015-11
dc.descriptionA THESIS SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES, AHMADU BELLO UNIVERSITY, ZARIA. IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD OF DOCTOR OF PHILOSOPHY IN PHYSICAL CHEMISTRY DEPARTMENT OF CHEMISTRY, FACULTY OF SCIENCE, AHMADU BELLO UNIVERSITY, ZARIA, NIGERIAen_US
dc.description.abstractIn this thesis, the ethanol extracts of some plant namely: Phyllanthus amarus (PA); Paullina pinnata (PP); Parinari polyandra (PP1); and Boscia senegalensis (BS) were investigated for their corrosion inhibition potential on mild steel and aluminium in HCl (1.0 M) and H2SO4 (0.5 M) respectively using gravimetric and linear polarization methods. The influence of extract concentrations (0.1g/l to 0.5g/l) and temperatures (303K to 323K) on corrosion and corrosion inhibition was assessed. The results obtained showed that PP, PA, BS and PP1 decreased the corrosion rate of mild steel and aluminium in the acid media. The rate generally decreased with increasing extract concentration in the order: PP> PP1> BS> PA and PP> BS> PP1> PA in HCl and H2SO4 respectively for aluminium; PP> PA> PP1> BS and BS> PP> PP1> PA in HCl and H2SO4 respectively for mild steel at 303 K. The corresponding maximum inhibition efficiencies were 73.55% and 40.00% for aluminium in HCl and H2SO4 respectively and 83.52% and 80.29% for mild steel. Inhibition efficiency in all the systems decreased with rise in temperature, suggesting physical adsorption of the extract constituents on the metal surfaces. Scanning electron microscopy (SEM) and infra-red (FTIR) spectroscopy analyses of the metal surfaces in the presence and absence of the inhibitors confirmed the presence of adsorbed protective layers. Linear polarization studies showed that the plant extracts suppressed both the anodic and cathodic half reactions of the corrosion processes, thereby acting as mixed-type inhibitors. Langmuir isotherm was found to be the best in describing the adsorption behaviour of the extract on the surfaces of mild steel and aluminium at room temperature, whereas the adsorption property at elevated temperature was best described by the Freundlich isotherm. Calculated values of free energy of adsorption, , on mild steel in the presence of PP, PA, BS and PP1 are as follows: -9.93 to -10.31 kJ mol-1 and -8.31 to -10.73 kJ mol-1 in HCl at 303 and 333K respectively, and -9.39 to -10.32 kJ mol-1 and -7.68 to -13.58 kJ mol-1 in H2SO4 at 303 and 333K respectively. The calculated values for the corrosion of aluminium in the presence of PP, PA, BS and PP1 follows the order: -9.01 to -9.53 kJ mol-1 and -7.91 to -9.58 kJ mol-1 in HCl at 303 and 333K respectively. Corrosion activation energy (Ea) values for mild steel and aluminium in the acids solutions increased in the presence of the inhibitor and the values were found to be less than 80kJmol-1 supporting the proposed physiosorption of the extract constituents. Density functional theory (DFT) based molecular dynamics simulations were adopted to theoretically describe the interactions of selected extract constituents with the metal surfaces. The computed binding energy values (Ebinding) for the various constituent indicate the adsorption process to be non-covalent (physiosorption).en_US
dc.identifier.urihttps://kubanni.abu.edu.ng/handle/123456789/8098
dc.language.isoenen_US
dc.subjectEXPERIMENTAL,en_US
dc.subjectCOMPUTATIONAL STUDIES,en_US
dc.subjectCORROSION,en_US
dc.subjectHIBITION POTENTIAL,en_US
dc.subjectSELECTED PLANT EXTRACTS,en_US
dc.subjectCORROSION,en_US
dc.subjectMILD STEEL,en_US
dc.subjectALUMINIUM,en_US
dc.subjectACID MEDIUM,en_US
dc.titleEXPERIMENTAL AND COMPUTATIONAL STUDIES OF CORROSION IN HIBITION POTENTIAL OF SELECTED PLANT EXTRACTS ON CORROSION OF MILD STEEL AND ALUMINIUM IN ACID MEDIUMen_US
dc.typeThesisen_US
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