Some Structural Effects of Organic N-Containing Compounds on Corrosion Inhibition^⋆

Investigation of some of the distinguishing factors in the molecular structure of a group of amines which are effective inhibitors in strong acid solutions is discussed. pK_a values of various amines were determined and estimation made of the approximate area of the metal surface which each amine molecule would cover in the adsorbed position. Three types of corrosion rate measurements were taken in inhibited and uninhibited acid solutions. Weight loss and gas evolution measurements at the boiling temperature were taken on coupons from steel rounds. A comparison of the inhibitor efficiencies within a series of cyclic imines and secondary amines shows differences which are clearly related to differences in their molecular structure. Overall results showed that there is little direct dependence of inhibitor efficiency on surface area covered by the amine. Also, there appeared to be no direct dependence of inhibitor efficiency on number of CH₂ groups, or its related parameters such as solubility. 5.8.4, 4.3.2