Cynthia E. Ogukwe

Broad spectrum corrosion inhibition: corrosion and microbial (SRB) growth inhibiting effects of Piper guineense extract

To assess the prospect of exploiting biomass extracts for the simultaneous control of chemical- and microbial-influenced corrosion, we herein describe experimental and computational studies to probe the corrosion inhibition and biocidal efficacy of aqueous extracts of Piper guineense (PG). Proximate phytochemical analysis of PG revealed the presence of alkaloids (3.1%), tannins (0.9%) and saponins (11.0%). The corrosion-inhibiting effect of the extract was appraised on low-carbon steel corrosion in 1-M HCl and 0.5-M H2SO4 using gravimetric and electrochemical techniques, whereas the agar disc diffusion method was employed to determine the biocidal effect of the extract on the corrosion-associated sulfate-reducing bacteria (SRB), Desulfotomaculum species. PG was found to be an excellent inhibitor for both corrosion and SRB growth. Both effects are attributed to the phytochemical constituents present in the extract. The corrosion process was inhibited by adsorption of the extract organic matter on the steel surface, whereas the antimicrobial effect results from disruption of the growth and essential metabolic functions of the SRB. We have relied on quantum chemical computations and molecular dynamics simulations to highlight the individual contributions of some extract constituents to the observed corrosion-inhibiting effect.

Corrosion Inhibiting Effect of Aframomum melegueta Extracts and Adsorption Characteristics of the Active Constituents on Mild Steel in Acidic Media

The extract from the seeds of Aframomum Melegueta (AM) was investigated as corrosion inhibitor for mild steel in aerated 1 M HCl and 0.5 M H2SO4 solutions using gravimetric and electrochemical techniques. AM extract was found to inhibit both the cathodic and anodic partial reactions of the corrosion process, via adsorption of the organic matter on the metal/solution interface, as described by the Langmuir as well as Flory-Huggins adsorption isotherms. Corrosion rates in all systems studied increased with rise in temperature. Increasing the temperature of the system enhanced inhibition efficiency of AM extract in 1 M HCl, but decreased efficiency in 0.5 M H2SO4. Molecular dynamics simulations were performed to theoretically illustrate the electronic structure and adsorption behaviour of the active constituents of the seeds of Aframomum melegueta; paradol (1-(4-Hydroxy-3-methoxyphenyl)decan-3-one) and shogaol ((E)-1-(4-Hydroxy-3- methoxyphenyl)dec-4-en-3-one) in order to theoretically evaluate their contributions to the corrosion inhibiting action of the extract.

Exploiting the Anticorrosion Effects of Vernonia Amygdalina Extract for Protection of Mild Steel in Acidic Environments

The corrosion protection of mild steel in 1 M HCl and 0.5 M H2SO4 solutions by ethanol extract of Vernonia amygdalina (VA) was studied using a combination of experimental and computational methods. The obtained results revealed that VA reduced the corrosion of mild steel in both environments and inhibition efficiency increased with VA concentration but decreased with prolonged exposure. Electrochemical results showed that the extract functioned via mixed corrosion inhibiting mechanism by adsorption of some organic constituents of the extract on the metal/acid interface. Findings from infrared spectroscopy and electron microscopy all confirmed that VA retarded mild steel corrosion in both 1 M HCl and 0.5 M H2SO4 through an adsorption process. The adsorption behavior of selected constituents of the extract was modeled using density functional theory computations.