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Weight loss, polarization, and open circuit potential methods were used to investigate the corrosion inhibitory impact of Centrosema pubescens leaf extract on 304L austenitic stainless steel UNS S30403 in 1 M hydrochloric acid. This non-toxic extract behaves as a mixed-type inhibitor according to the polarization curves, thermodynamics and activation parameters. Both the weight loss calculations and potentiodynamic polarization investigations showed that 1.2 g L-1 was the optimal concentration of the leaf extract. While the weight loss method gave inhibition efficiency of 86.84 and 75.00 % after 10 and 60 days of immersion at the optimum concentration, polarization studies revealed inhibition efficiencies of 93.08 and 98.66 % at 303 and 333 K, respectively. The extract molecules adhered to the UNS S30403 surface according to Langmuir adsorption isotherm. The presence of the protective film on the UNS S30403 surface was confirmed by SEM, EDX, and XRD measurements. The inhibition performance of the leaf extract was noted to be a function of the extract concentration, immersion time and temperature. The FTIR analysis indicated an interaction between austenitic stainless steel UNS S30403 and the molecules of Centrosema pubescens leaf extract.

From gravimetric studies, hybrid nano-coatings, based on permanganate/fluo­ride/gly­cerol conversion coating solutions formed on aluminum alloy by immersion procedures developed rapidly at a rate which decreased with time of treatment and was about 16 mg in weight after a period of three minutes. The morphology of the coating during scanning electron microscopic (SEM) examinations revealed randomly shaped coating materials with mud cracking patterns, characteristics of dried out coatings derived from gel-like materials. Analyses of the coating using EDX attachment in the SEM showed that it was composed essentially of aluminum, oxygen and manganese compounds, probably hydrated. The corrosion resistance of the coating out-performed ‘bare’ aluminum alloy specimens exposed to natural environment and 1 M sodium chloride solution. The coating improved the paint adhesion characteristics of the substrate aluminum alloy.

This study investigates the inhibition potential of Vernonia amygdalina stem extract (VAE) on the corrosion of mild carbon steel immersed in 1 M HCl solution containing various concentrations of the inhibitor. The corrosion rate and inhibition efficiency were evaluated using mass loss and adsorption techniques. The results revealed that VAE efficiently inhibits the corrosion rate of mild carbon steel immersed in the acidic medium. The concentration of 0.6 g/L provides the highest inhibition efficiency of 78.1 %. The adsorption process was consistent with the physisorption mechanism and obeyed the Langmuir isotherm. The functional groups responsible for inhibition were identified using Fourier Transform Infrared (FTIR) spectra. The surface morphology of the corroded samples examined with Scanning Electron Microscope (SEM) revealed the presence of protective oxide layer. Inhibition efficiency was found depended on the presence of oxalate, phytate, tannins, saponins and flavonoids in the VAE. It has been concluded that VAE is safe, cheap and efficient corrosion inhibitor for mild carbon steel.