The Erosion-Corrosion Inhibition of AISI 431 Martensitic Stainless Steel in 2.0 M H2SO4 Solution Using N-Alkyl Quaternary Ammonium Salts as Inhibitors

Electrochemical measurements were performed to explore the influence of cationic surfactants on the corrosion inhibition in the moving fluid with and without abrasive particles. The surfactants of the type of N-alkyl quaternary ammonium salts with different chain length (myristyltrimethylammonium bromide, chloride MTABr, MTACl and trioctylmethylammonium bromide, chloride TOMABr, TOMACl) were used as corrosion inhibitors for martensitic stainless steel type AISI 431 in 2 M H2SO4 solution. The polarization data showed that both surfactants used in this study acted as mixed type inhibitors, adsorbing on the stainless steel surface in agreement with the Flory-Huggins adsorption isotherm. Good inhibitory properties were achieved, only when the concentration of added surfactants exceeded their CMC values. It seems that the moving medium makes it difficult for the surfactants to adsorb on the metal surface, even when no abrasive particles are added. The number of -CH2 groups (clustered chain surfactants) had shown a significant effect on the inhibition efficiency of the investigated system. The inhibitory action of n-alkyl quaternary ammonium salts in 2.0 M H2SO4 mainly results from the physical (electrostatic) adsorption of the N-alkyl ammonium ions on the negatively charged surface of stainless steel.