Study of corrosion inhibition of carbon steel by dithiolethione organic compounds in a chlorured medium

Abstract EN

Two derivatives of dithioles-1, 2 thiones-3 and their salts namely (1) : 4-phényl-1, 2-dithiol-3-thione, (2) : 4p-tolyl-1, 2-dithiol-3-thione, (3) : 3-méthylthio-4-phényl-1,2-dithiolylium and (4) : 3-méthylthio-4p-tolyl- 1, 2--dithiolylium were synthesized and their inhibition of corrosion of carbon steel in HCl solution with pH = 6.5 was investigated by electrochemical techniques.

Inhibition efficiency of various concentrations of these compounds was determined at room temperature.

The four compounds showed a best performance, giving inhibition efficiency higher than 93%, even at a very low concentration, the inhibition efficiency of them follows the order (1) < (2) < (3) < (4).

Experiences show that dithiolethione salts derivatives are better inhibitors than their origin dithiolethiones.

With 100 ppm the inhibition efficiency is 93, 36 %for the first inhibitor and 95.57% for the second.

Only with 25 ppm the inhibition efficiency is 98, 67 %for the first salt and 99.10% for the second salt.

Potentiodynamic polarization studies indicated that all four compounds acted predominantly as mixed inhibitors, with adsorption from HCl solution on carbon steel surfaces obeying Temkin’s adsorption isotherm.

The heterogeneous factors, giving variation of adsorption energy with coverage, have been calculated for all inhibitors.

The lower is this factor the higher is the inhibition efficiency.

These observations are confirmed by computer calculation of molecule dipoles and electronic densities.

For each molecule, dipole and electronic densities have high values and increase as their inhibition efficiencies increase.

The values of salt inhibitor dipoles are higher comparatively with those of their origin compounds : 3.543 Debye and 3.846 Debye for inhibitor (1) and (2), their salts have 5, 441 Debye and 5.825 Debye respectively.