Ethanolamines as corrosion inhibitors for zinc in phosphoric acid medium

The corrosion of zinc in phosphoric acid containing ethanolamines has been studied at different acid concentrations and temperatures. Corrosion increases with increase in acid concentration and temperature. At constant acid concentration, the inhibition efficiency of ethanolamines decreases with their concentration. At constant inhibitor concentration, the inhibition efficiency increases with the concentration of acid. At 80 mM inhibitor concentration in 0.01 M phosphoric acid at 301K for a 24 h immersion period, the efficiency of inhibitors decreases in the order: ethanolamine (100.0%) > diethanolamine (98.7%) > triethanolamine (97.3%). As the temperature was increased, the value of Delta G degrees a increased, while the percentage inhibition decreased. The mode of inhibition action appears to be chemisorption since a plot of log (theta/1-theta) vs. log C gave a straight line, which suggested that the inhibitors covered both the anodic and cathodic regions through general adsorption following the Langmuir isotherm. Anodic and cathodic galvanostatic polarisation curves show little cathodic but significant anodic polarization.