Optimisation des procédés d’inhibition de la corrosion électrochimique de l’acier C38 par des extraits d’alcaloïdes

Abstract

In this work, alkaloids extract was studied as the corrosion inhibitor for C38 steel in 1 M HCl and 0.5 M H2SO4 using electrochemical and surface analysis and the application of spectroscopic technique for study corrosion in 1 M HCl medium. To achieve this study, the alkaloids were extracted and characterized using appropriate chemical techniques. 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. The inhibition efficiency increased from 90 % to 96 % at room temperature for AERMS 100 mg/L + 1 mM KI. This efficiency remained high for temperatures 40 °C; 50 °C and 60 °C. For the determination of the inhibition mechanism, 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. Finally, the plant alkaloid Voacangine with a hindered basic nitrogen atom was examined as an inhibitor of corrosion of steel in 1 M HCl. The study was carried out using a comparative approach where several independent methods (spectroscopic solution analysis, electrochemical impedance, potentiodynamic polarisation and mass loss measurements) were performed in order to strengthen the validity of the results. All the findings revealed to be in close agreement with each other. The spectroscopic solution analysis can be used to evaluate the corrosion of the steel in acid solution. The obtained interesting results confirmed that the alkaloids are good corrosion inhibitors for C38 steel in acid solutions when these contain halides ions.