Investigation of the synergistic effect of anodic and cathodic contact inhibitors in steel corrosion protection

In this study, a corrosion inhibitor was synthesized through the condensation reaction involving triglyceride (soybean oil), diethanolamine, and boric acid, resulting in the formation of amides of high carboxylic acids (HCAA). Experiments were conducted to determine the optimal composition and conditions for producing an inhibitor with enhanced anti -corrosion properties. The variation in reagent ratios and reaction time was investigated in the temperature range of 180 -200 degrees C. Utilizing IR spectroscopy, the presence of esters and amides in the products was confirmed, along with an examination of the dependence of inhibitor composition on reaction parameters. The amine number was determined for all synthesized products, and their solubility was assessed at a concentration of 16% in non - polar solvents at 25 degrees C. To evaluate the corrosion inhibition performance of cathodic and anodic inhibitors, as well as their combinations, two organic compounds with different functional groups were selected. Amides of high carboxylic acids, possessing amide and hydroxyl groups, exhibit reducing properties. Nitrated oil, featuring oxidizing properties due to its nitro groups, served as the second inhibitor. A synergistic effect was observed upon mixing cathodic and anodic inhibitors at a mass ratio of 1:1. Potentiometric analysis indicated that the HCAA inhibitor decelerates the cathodic and accelerates the anodic reaction, resulting in a negative shift in the corrosion potential. Conversely, nitrated oil accelerates the cathodic reaction and decelerates the anodic reaction, leading to a positive shift in the corrosion potential. Consequently, the synthesized product from triglyceride, diethanolamine, boric acid, and nitrated oil acts as cathodic and anodic inhibitors. This inhibitor mixture slightly shifts the corrosion potential in a positive direction ( Delta E (corr) = 55 mV) compared to E corr in oil and suppresses both cathodic and anodic processes. Hence, this composition can be classified as mixed corrosion inhibitors of the chemisorption type.