Corrosion inhibition of aluminum in 1 M HCl by novel pyrimidine derivatives, EFM measurements, DFT calculations and MD simulation

Abstract

• Pyridine-pyrimidine derivatives inhibit aluminum corrosion in the protonated form. • Adsorption of inhibitors is spontaneous and is physical–chemical adsorption. • Characteristic molecular parameters are explored using DFT and MD. • Surface analysis results indicate the presence of a protective surface layer. • EMMD has the greatest inhibition efficiency theoretically and experimentally. Four pyridine-pyrimidine derivatives, namely pyridine-2,6-diamine (PD), pyrimidine-2-amine (PA), 6-amino-3,4-dihydropyrimidine-2(1H)-thione (ADT) and ethyl (R)-6-(4-chlorophenyl)-2-mercapto-4-methyl-1,6-dihydropyrimidine-5-carboxylate (EMMD) are used as effective inhibitors for aluminum corrosion in 1 M HCl solution. The anti-corrosive potential of these heterocyclic compounds has been evaluated by electrochemical frequency modulation (EFM) method, The inhibition efficiency of these inhibitors was strongly associated to the concentration (10 −7 –10 −3 M) and the structure of the molecules; reached a maximum of 95.68% for EMMD at 10 −3 M owing to more anchoring functional groups. The effect of temperature on the corrosion behaviour was assessed at solution temperature range 298–323 K. The four inhibitors adsorbed according to the Langmuir’s adsorption isotherm. Thermodynamic activation parameters for the dissolution process of aluminum in 1 M HCl and inhibited solutions were calculated and discussed. Surface analysis (SEM, EDX, and AFM) confirmed the formation of a protective layer adsorbed on the aluminum surface. In addition, theoretical studies by DFT and MD revealed the correlation between the molecular chemical structure of studied inhibitors and their inhibition efficiency. The adsorption mechanism is revealed by theoretical calculations.