Ethanolamines as corrosion inhibitors for zinc in nitric acid

The corrosion of zinc in nitric acid containing ethanolamine, diethanolamine and triethanolamine has been studied at different acid concentrations, inhibitor concentrations and temperatures. Corrosion increased with the concentration of the acid and with temperature. At constant acid concentration, the inhibition efficiency of ethanolamines increased with the concentration. At constant inhibitor concentration, the inhibition efficiency increased with the concentration of the acid. At 40 mM inhibitor concentration in 0.01 M HNO3 acid at 301 K for a 24-h immersion period, the efficiency of inhibitors decreased in the order: ethanolamine (95%) > diethanolamine (93%) > triethanolamine (88%). As the temperature was increased, the value of DeltaG(a) increased, while the percentage of inhibition decreased. The mode of inhibition action appears to be chemisorption since the plot of log (theta/1 - theta) versus log C gave a straight line, which suggested that the inhibitors covered both anodic and cathodic regions through general adsorption following the Langmuir isotherm. Anodic and cathodic galvanostatic polarization curves showed little anodic but significant cathodic polarization.