Surface Activity and Electrochemical Behavior of Some Thiazine Cationic Surfactants and Their Efficiency as Corrosion Inhibitors for Carbon Steel in a Sour Environment.

The inhibition efficiency of cationic surfactants such as 1-ethyl-4H-benzo[d][1,3]thiazin-1-ium bromide (BTB) and N-ethyl-N,N-dioctyloctan-1-aminium bromide (DAB) for X-65 type carbon steel in oil well formation water under a H2S environment has been studied using potentiodynamic polarization and electrochemical impedance spectroscopy measurements. Fourier transform infrared and nuclear magnetic resonance spectroscopy techniques were used to confirm the chemical structures of BTB and DAB. The novelty of this work lies in modifying the long chains in the inhibitor, which leads to high efficiency. These surfactants act as good inhibitors, which inhibit both cathodic and anodic routes by adsorption on the electrode surface, which is compatible with the critical micelle concentration parameters, together with a slight positive change in the corrosion potential (Ecorr). The IE% reached 93.4% for compound BTB and 84% for compound DAB at 250 ppm. The equivalent circuit was used to analyze the model of the corrosion inhibition process. The atomic force microscopy image shows the morphology of the adsorbed layer formed on the steel alloy. Finally, a suitable inhibition mechanism was proposed.