Aim: 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.
Background: 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.
Objective: 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.
Methods: 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.
Results: 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.
Conclusion: 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.