The efficiency of three heterocyclic compounds, 3-amino-1,2,4-triazole, 4-hydroxy-2H-1-benzopyran-2-one and 4-hydroxy-3-(1H-1,2,4-triazole-3-ylazo)-2H-1-benzopyran-2-one (abbreviated 3-ATA, 4-HQ and 3-ATA-Q, respectively) as steel corrosion inhibitors in 3.5% NaCl has been investigated by Tafel extrapolation and linear polarization methods. Corrosion parameters and adsorption isotherms were determined from current-potential curves. It was found that inhibition efficiencies (g%) and surface coverage (h) increase with an increase in the concentration of 3-ATA and 3-ATA-Q. However, 4-HQ accelerates the corrosion rate as its concentration increases. The adsorption of 3-ATA and 3-ATA-Q on the steel surface obey Langmuir isotherm. A clear correlation was found between corrosion inhibition efficiency and theoretical parameters obtained by the density functional B3LYP/6-31g(d) method. The experimental results are supported by the theoretical data.

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