PLANT EXTRACT-NANOPARTICLES HYBRID AS CORROSION INHIBITORS FOR AA2024 ALUMINIUM ALLOY
PLANT EXTRACT-NANOPARTICLES HYBRID AS CORROSION INHIBITORS FOR AA2024 ALUMINIUM ALLOY
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Date
2013-05
Authors
KASIM, Auwal
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Abstract
ABSTRACT
The influence of two plant extracts, Parkia biglobosa (African locust bean) and Vitex
doniana (Black plum) on electrochemical corrosion behaviour of as-cast AA2024
aluminium alloy exposed to artificial sea water (3.5%NaCl solution) was investigated.
The results of the 1H NMR-based metabolomics of leave extracts of Parkia biglobosa
(PBE) and Vitex doniana (VDE) revealed aromatic and other functional groups such as
–CH3, and R-OH which are attributes of a good inhibitor. The performances of these
extracts were evaluated individually, synergistically and under the influence of Boehmite
Nanoparticles in different amounts of 0.1, 0.2, 0.3, 0.4 and 0.5g. Parkia biglobosa extracts
gave better Inhibition Efficiencies (IE%) than Vitex doniana extracts whether alone or in
synergistic combinations; this could probably be due to the high density/concentration of
aromatics and other functional groups as revealed by 1H NMR-based spectrum.
Comparison of the performances of the different extract-extract and extract-Nanoparticle
systems were also made on the basis of Inhibition Efficiencies (IE%), determined from
both chemical (Gravimetric-based Mass Loss) and electrochemical techniques (Linear
Polarisation Resistance and Electrochemical Impedance Spectroscopy). Only
PBE+VDE+Boehmite Nanoparticle synergistic system was found to compare favourably
with Sodium chromate, the reference inhibitor against which the effectiveness of the
different inhibitor systems (single, binary and ternary) was compared. An optimum IE%
of 92.15% for PBE+VDE+Boehmite Nanoparticles system compared favourably with
IE% of 92.57% for Sodium Chromate. The adsorbed films of Sodium Chromate and
PBE+VDE+Boehmite Nanoparticles systems were found to be stable around -0.6V when
evaluated by Chronopotentiometry. The synergism parameters were found to be greater
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than unity, affirming synergy among the inhibitor molecules/ions. Kinetic and
thermodynamic data generated suggested co-adsorption through a combination of both
Physisorption and Chemisorption mode of interaction between the inhibitors and the
substrates. The linearity of Langmuir adsorption Isotherms further supported adsorption
proposition, while the El-Awady’s adsorption Isotherms consolidated the Langmuir’s
model by calculating the number of active sites; obtained values greater than unity
inferred that the inhibitor molecules occupied more than one site. SEM/EDX panorama
of the inhibited samples revealed evidences of interference of corrosion products with the
additive substances to form new phases, as revealed by X-Ray Diffractograms, which
was a plausible mechanism for the action of the inhibitors, and not just adsorption or coadsorption.
Raman spectroscopic analyses were found to be particularly helpful when
examining the surfaces of the substrates inhibited by the plant extracts. Variations in
Raman shifts were indicative of surface interactions; due either to adsorption of organic
molecules onto the alloy surfaces or release of certain metal ions into solution, leading to
appearance of certain peaks. All the characterisation techniques, using SEM/EDX, XRD
and Raman Spectroscopy, gave insights into the influence of the additive substances on
the electrodes/substrates. This was achieved through morphological revelations, phase
identifications and other thin corrosion products elucidation. IE% results obtained from
Linear Polarisation Resistance, Electrochemical Impedance Spectroscopy and
Gravimetric-based mass loss were compared using ANOVA statistical tool and found to
be in good agreement. In conclusion, PBE+VDE+Boehmite Nanoparticles system could
serve as an ecofriendly alternative to Sodium Chromate.
Description
A PH.D DISSERTATION SUBMITTED TO THE SCHOOL OF POSTGRADUATE
STUDIES, AHMADU BELLO UNIVERSITY, ZARIA IN PARTIAL FULFILMENT OF
THE REQUIREMENTS FOR THE AWARD OF A DOCTOR OF PHILOSOPHY
DEGREE IN METALLURGICAL AND MATERIALS ENGINEERING.
Keywords
PLANT EXTRACT, NANOPARTICLES HYBRID, CORROSION INHIBITORS, AA2024 ALUMINIUM ALLOY