Corrosion Protection for Cast Iron in Sulfamic Acid Solutions and Studies of the Cooperative Effect Between Cationic Surfactant and Acid Counterions

Abstract

The electrochemical behavior of white cast iron in sulfamic acid was studied in the presence of hexadecyltrimethylammonium bromide as a corrosion inhibitor. The cooperative effect between counterions of sulfamic acid and CTAB was investigated as well as the impact of this phenomenon on the inhibition efficiency; for that purpose, gravimetric method, electrochemical impedance spectroscopy, potentiodynamic polarization curves and inductively coupled plasma spectrometry (ICP-OES) techniques were exploited. The CTAB molecule reveals remarkable qualities for the protection of white cast iron in sulfamic acid cleaning solutions. Sulfamate ions play a major role in this phenomenon by facilitating the attraction and adsorption of CTAB onto the surface of white cast iron. The inhibition efficiency remains almost stable (about 95%) for a concentration of 10−3 M in CTAB. The critical micelle concentration of CTAB in the H2O/NH2SO3H system was investigated by the conductimetry method. The CTAB adsorption onto the cast iron surface was studied by Langmuir adsorption isotherms. The surface characterization by RDX and SEM showed a good anticorrosion protection and a lower surface roughness in the presence of CTAB.