12-Aminododecanoic acid as a corrosion inhibitor for carbon steel

The inhibiting effect of 12-aminododecanoic acid (AA) on corrosion of carbon steel (CS) was investigated in hydrochloric acid of different pH, temperatures and over a prolonged period of time, and also in some other selected corrosive solutions. It was found that AA inhibits both partial corrosion reactions, with a slightly stronger inhibition of the anodic corrosion reaction. The corrosion protection mechanism is by formation of a surface-adsorbed AA monolayer that offers a hydrophobic barrier to transport of solvated corrosive ions to the surface. A maximum inhibition efficiency of 98.8 ± 0.5% was achieved in 0.5 M HCl. The adsorption of AA onto the CS surface was described by the Langmuir adsorption isotherm. The corresponding standard Gibbs energy of adsorption was calculated to be −26 kJ mol⁻¹. Polarization modulation infrared reflection absorption spectroscopy measurements revealed that the adsorbed AA monolayer is amorphous, which is due to the high heterogeneity of the CS surface.