Effects Of Imidazoline Quaternary Ammonium Salt On Pitting Behavior For Q235Carbon Steel

Pitting is one of typical corrosion failures for passive metals. A important problem is how we control and predict pitting because it is stronger hidden, radom and destructive. Adding inhibitor is an effective method to control corrosion, but many studies focused on uniform corrosion rather than localized corrosion. Specially, the influences of organic inbitor on pitting and metstable pitting behviour have less been studied. In this work, the influences of imidazoline quaternary ammonium salt on pitting and metstable of Q235carbon steel in0.01mol/LNaCl+0.1mol/LNaNO2soltuions were studied by potentiodynamic polarization, electrochemical impendance spectroscopy (EIS), Mott-Schottky curve, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and electrochemical scanning tunneling microscopy (ESTM), the results are as follows:(1) The additions of imidazoline quaternary ammonium salt as an anodic inhibitor can reduce the corrosion current and passive current of carbon steel. To some degree, the imidazoline quaternary ammonium salt can promote the formation of passive film on carbon steel surface, although it has less influence on pitting potential. The imidazoline quaternary ammonium salt with appropriate amount can obviously accelerate the repassivation of pit. The proper addition of imidazoline quaternary ammonium salt is about40mg/L.(2) Imidazoline quaternary ammonium salt can be absoded on the passive film, decrease donor concentration of the n-type semiconductor film, increase the film resistance, and further improve the corrosion resistance of carbon steel.(3) Under the condition of potentiostat polarization (Eb), the potential distribution of carbon steel surface is not obvious uniform, and there are many active anodic areas on the steel surface. After imidazoline quaternary ammonium salt is added in0.01mol/L NaCl+0.1mol/L NaNO2solution, due to its absorption on the passive film surface, the active anodic areas decrease and pitting is inhibited to some degree.(4) When the pH values of NaCl+NaNO2solutions are adjusted to10, the change tendencies of piting potential, protection potential, metstable pitting potential with the additions of imidazoline quaternary ammonium salt are similar to those in unadjusted pH solutions. But at pH=10, carbon steel has a better resistance of pitting. At pH=4, a bigger passive current density is observed. This shows that decreasing pH value of solution reduce corrosion resistance of passive film.(5) In NaCl+NaNO2solutions without imidazoline quaternary ammonium salt, the peak current density of metstable pitting decreases with increasing pH values, showing a more concentrated distribution. After adding imidazoline quaternary ammonium salt, in a higher pH solution, the film resistance of carbon steel surface becomes bigger, the donor concentration decrease, and the nucleation numbers of metstable pit decrease.