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This paper aims to evaluate the inhibitive action of the corrosion of mild steel in sulphuric acid solutions by ethanol extracts of Thymus vulgaris (TYV), Xylopia aethiopica (XYA) and Zingiber officinale (ZGO) as eco-friendly and non-toxic mild-steel corrosion inhibitors in H₂SO₄ solutions.

Ethanol extracts of TYV leaves, XYA fruits and ZGO roots were used as inhibitors in various corrosion tests. Gravimetric and gasometric techniques were used to characterize the mechanism of inhibition.

Results indicate that the extracts inhibit the corrosion process efficiently. Inhibition efficiency was found to increase with an increase in extract concentration and decrease with an increase in temperature. Inhibition efficiencies followed the trend TYV > ZGO > XYA. Thermodynamic considerations revealed that the energy of activation increased in the presence of the plant extracts. Adsorption of the plant extracts on mild steel surface occurred spontaneously, and E_a and ΔG_ads values confirm a physical adsorption processes. Phytochemical studies showed the presence of saponoids, flavonoids and polyphenols whose attachment to adsorption sites on the metal surface is responsible for the inhibition process. Experimental data fit the Langmuir adsorption isotherm.

The plant extracts can be used in chemical cleaning and picking processes.

The research provides information on the possible use of the ethanol extracts from TYV leaves, XYA fruits and ZGO roots as sources of cheap, eco-friendly and non-toxic corrosion inhibitors.

The purpose of this paper is to study the adsorption properties of a proven traditional medicine of West Africa origin, Alstonia boonei with an attempt to evaluate its application in the corrosion protection of mild steel in 5 M H₂SO₄ and 5 M HCl.

Phytochemical screening and Fourier transform infrared spectroscopy analysis were used to characterize the methanolic extract of the plant. Gravimetry, gasometry and electrochemical techniques were used in the corrosion inhibition studies of the extract and computational studies were used to describe the electronic and adsorption properties of eugenol, the most abundant phytochemical in Alstonia boonei.

The extract acted as a mixed-type inhibitor in both acidic solutions, with improved inhibition efficiency achieved with increasing concentration. While the efficiency increased with temperature for the HCl system, it decreased for the H₂SO₄ system. The mechanism of adsorption proposed for Alstonia boonei was chemisorption in the HCl system and physisorption in the H₂SO₄ system, and the adsorptions obeyed Langmuir isotherm at low temperatures. Computational parameters showed that eugenol, being a representative of Alstonia boonei, possesses excellent adsorption properties and has the potential to compete with other established plant-based corrosion inhibitors.

As opposed to pure compounds with distinctive corrosion effects, plant extracts are generally composed of a myriad of phytoconstituents that competitively promote or inhibit the corrosion process and their net effect is evident as inhibition efficiencies. This is, therefore, the main research limitation associated with the corrosion inhibition study of Alstonia boonei.

Being very rich in antioxidant properties by its proven curative and preventive effects for diseases, the interest was stimulated towards the attractive results that abound from its corrosion protection of metals via its anti-oxidation route.