Cetyl Trimethyl Ammonium Bromide as Anti-Pit Agent for Mild Steel in Sulfuric Acid Medium

Abstract

Pitting corrosion is a very serious problem for mild steel when it comes in contact with the dilute sulfuric acid medium. Specialized corrosion inhibitors are essentially required to minimize pitting and uniform types of corrosion in mild steel. Most of the corrosion inhibitors discovered so far protects the mild steel from uniform type of corrosion. But pitting corrosion is more fatal than a uniform type of corrosion because it immediately makes mild steel unfit for use as leakage starts from the pit. The objective was to protect the mild steel alloys from pitting corrosion when comes in contact with dilute sulfuric acid by the use of organic corrosion inhibitor. Cetyl Trimethyl Ammonium Bromide (CTAB) is tested as a corrosion inhibitor for mild steel in 0.1 N H2SO4 as corroding medium at 25.0, 30.0 and 35.0°C by weight loss, electrochemical polarization, and Impedance spectroscopy methods. Surface study of corroded and un-corroded specimens of mild steel was carried out by Metallurgical Research Microscopy (MRM) and Scanning Electron Microscopy (SEM) techniques. Surface study confirms that the adsorption of CTAB takes place through nitrogen atom resulting in the formation of uniform, nonporous, passive film confirmed by decrease in Warburg Impedance (Zw), decrease in Faradaic current, increase in Capacitive current, an increase in charge transfer resistance, Rct (41 to 401 Ω cm2) and significant increase in capacitive loop in Nyquist plot with increase in concentration of CTAB which results in significant decrease in corrosion rate of mild steel in 0.1N H2SO4 medium (percentage corrosion inhibition efficiency: 95.0%) especially eradicating pitting type of corrosion. CTAB was proved to be a very good anti-pit agent for mild steel in 0.1N sulfuric acid medium. Pitting and uniform type of corrosion was significantly reduced by the use of CTAB as corrosion inhibitor for mild steel in the dilute sulfuric acid medium at 25.0, 30.0 and 35.0°C.