Role of hydroxyl group in the inhibitive action of benzoic acid toward corrosion of aluminum in nitric acid

Corrosion inhibition action of benzoic acid, p-hydroxy benzoic acid, 2-4-di hydroxy benzoic acid, and 3-4-5-trihydroxy benzoic acid toward aluminum all oy 3003 (UNS A93003) in 20% (wt%) nitric acid (HNO3) using different concen trations of these compounds at 30 degrees C, 40 degrees C, and 50 degrees C has been studied thoroughly. 3-4-5-trihydroxy benzoic acid (inhibition eff iciency [IE]: 30% and 72%) was the most effective inhibitor followed by 2-4 -dihydroxy benzole acid (IE: 22% to 62%) p-hydroxy benzoic acid (IE: 11% to 52%), and benzoic acid (IE: 2.5% to 15%) IE increased with concentration a nd its maximum value was observed at 0.5% concentration of all inhibitors u sed. The percentage of IE of the inhibitors decreased with an increase in t emperature from 30 degrees C to 50 degrees C. Values of heat adsorption and activation energy were calculated from weight loss data, which came out in the range for the reaction occurring at the surface, The behavior of inhib itors studied deviated from the Langmuir isotherm, The IE of higher hydroxy species was improved when more hydroxy centers were added. Anodic and cath odic polarization curves were shifted toward lower current density regions in the presence of inhibitors. This revealed that they were mixed inhibitor s.