Performances of Alkaloid Extract from Rauvolfia macrophylla Stapf toward Corrosion Inhibition of C38 Steel in Acidic Media

Alkaloid extract from Rauvolfia macrophylla Stapf (AERMS) was studied as the corrosion inhibitor for C38 steel in 1 M HCl and 0.5 M H₂SO₄ using electrochemistry and surface analysis. The corrosion inhibition was efficient and proceeds via adsorption of AERMS on the steel surface due to the active functional groups present in the molecules. AERMS acts as a mixed inhibitor in HCl and as a cathodic inhibitor in H₂SO₄. In H₂SO₄ corrosive medium, the presence of iodides improves the adsorption of the alkaloid molecules by reducing the surface charge of the electrode and thus substantially decreases the corrosion rate. Two pure alkaloids (tetrahydroalastonine (THA) and perakine (PER)) were quantitatively isolated from AERMS, and their anticorrosive properties for C38 steel in 1 M HCl and 0.5 M H₂SO₄ were evaluated. THA showed the highest efficiency while the performance of PER was less important compared to the extract. This confirms that the efficiency of AERMS was the result of the complementary action of the chemical compounds present in the extract.