Anti-corrosion behaviour of lxora coccinea flower extract as a green corrosion inhibitor for mild steel in marine environment

The corrosion inhibition of mild steel immersed in 3.5% NaCl was assessed using a weight loss
method with an aqueous extract from lxora coccinea flower. Electrochemical (electrochemical
impedance spectroscopy and Potentiodynamic polarisation) and gravimetric techniques as well as
adsorption and surface analyses (scanning electron microscopy and Fourier transform infrared
spectroscopy) were employed to probe the corrosion process. Electrochemical experiments were
conducted at 298 K using 0 (blank), 50, 100, 150, 200 and 250 ppm of the extracts while gravimetric
experiments were carried out using the same range of concentration at different temperature values of
298, 303, 308, 313K in a thermostatic water bath for 8 h. The equilibrium corrosion data of the lxora
coccinea flower extract was well described by Langmuir adsorption isotherm. The values of Gibbs
free energies obtained at all experimental temperatures ranged between − 11.64 kJ/mol and
− 0.2248 kJ/mol. These observations suggest that corrosion inhibition process occurred
spontaneously. Electrochemical studies were employed to explore the mechanisms behind the
inhibition. Results indicate that higher doses of the inhibitor reduce corrosion rates and increase
inhibition efficiency. The active components of the extract adhere to the metal surface, achieving a
maximum inhibition effectiveness of 97.40%. The polarization method demonstrated the inhibitor’s
ability to control both anodic and cathodic processes. SEM and AFM confirm the inhibitor prevents
rust in marine environment.