THE INHIBITION EFFECT OF THIAZINE COMPOUNDS TOWARDS THE CORROSION OF MILD STEEL IN SULPHURIC ACID MEDIA

Abstract

The inhibition effect of thiazines (AT, CBT & NBT) on mild steel corrosion in 1M sulphuric acid (H2SO4) was investigated by weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The result showed that corrosion rate was significantly decreased in presence of the inhibitors. The inhibiting action increases with the concentration of thiazine compounds to attain 99 % at 0.5mM of (AT). The increase in temperature leads to a decrease in the inhibition efficiency of the compounds in the temperature range 308-353K. Adsorption of thiazines on the mild steel surface in 1M H2SO4 obeyed the Langmuir adsorption isotherm. EIS measurements showed an increase in charge transfer resistance (Rct) with concentration. Potentiodynamic polarization study showed that the inhibitors act as mixed type, controlling both the anodic and cathodic reactions. Surface analysis by SEM confirmed the formation of adsorbed protective layer of the inhibitor on the steel surface.