Abstract
The synthesis of two novel organic inhibitors (1-ethyl-3-(5-mercapto-4-methyl-4H-1,2,4-triazol-3-yl)-7-methyl-1,8-naphthyridin-4(1H)-one) (abbreviated as CpdI) and (1-ethyl-7-methyl-3-(4-methyl-5-((4-methylbenzyl)thio)-4H-1,2,4-triazol-3-yl)-1,8-naphthyridin-4(1H)-one) (abbreviated as CpdII) on aluminum in 0.5 M NaOH was reported. The corrosion inhibition effect of the new inhibitors was studied by weight loss, electrochemical, and quantum chemical techniques. Results indicated that 1-ethyl-7-methyl-3-(4-methyl-5-((4-methylbenzyl)thio)-4H-1,2,4-triazol-3-yl)-1,8-naphthyridin-4(1H)-one) is more competent in NaOH than the other organic compound in a temperature range 25-45 degrees C. The results revealed that the protection efficiency increases with increasing concentration of potential inhibitors, time, and temperature. The two novel organic inhibitors are good inhibitors for the dissolution of aluminum in 0.5 M NaOH and they are mixed-type inhibitors. The values of standard free energy of adsorption (Delta G(ads)(0)) of - 15.0 kJ mol(-1) suggest the physical adsorption of CpdI and CpdII on the aluminum surface. In the temperature range studied, CpdI provided 20-45% inhibition efficiency, while the inhibition efficiency of CpdII varied within 50-85%. Adsorption study revealed the adsorption method of the synthesized inhibitors depends on the electronic characteristics and steric impacts of inhibitors in addition to the nature of aluminum surfaces. The adsorption of synthesized organic inhibitors on the surface of aluminum followed Temkin isotherm. The results of molecular DFT calculations agrees with the experimental data reported.