Abstract:
Corrosion is defined as a process that leads to the deterioration of metallic materials as a result of
interaction with corrosive environments. Corrosion inhibitors are added to several systems as a
form of protection against corrosion in a corrosive environment. The corrosion inhibitive effect of
hexane, acetone and ethanolic extracts of Thaumatococcus daniellii (Benn) leaves on mild steel in
hydrochloric acid solutions was investigated using electrochemical and gravimetric methods in
conjunction with surface analysis by scanning Electron Microscopy (SEM) and Fourier Transform
Infrared (FTIR) Spectroscopy. The experiments were conducted at varying concentrations (0−10
x 103 ppm) of extracts, temperature (298−323 K) and immersion times (24−96 h). The adsorption
isotherm studies were conducted using the Langmuir, Freundlich, Temkin and El-Awady models.
Results obtained included Electrochemical Impedance Spectroscopy, Potentiodynamic
Polarisation, kinetic, thermodynamic, and adsorption parameters. The results revealed that the
ethanolic extract of T. danielli leaves had the highest corrosion inhibitory potential as it contained
more corrosion inhibitory organic compounds. The kinetic data of the corrosion process followed
first order kinetic model. It was confirmed by potentiodynamic polarisation measurements that the
three extracts (hexane, acetone and ethanolic) were mixed-type inhibitor by action. The corrosion
process was endothermic and spontaneous with a level of disorderliness. The SEM micrographs
displayed the roughness of the metal surface in the absence of the three extracts and the smoothness
in the presence of the extracts. Important functional group bands of the phytochemicals were
revealed in the FTIR spectra
