engleski

Investigation of Applicability of Natural Tannin as Pickling Inhibitor for Low Carbon Steel

The efficiency of mimosa tannin as a low carbon steel corrosion inhibitor in 5% hydrochloric acid was determined by the weight loss method, in the range of temperatures from 20 to 60 C. The inhibitor concentration ranged from 10-6 to 10-2 mol dm-3. The inhibitor surface coverage increases with the increase in concentration and decreased with the increase in temperature. The Frumkin isotherm was fitted to the experimental data. The free energies, the enthalpy and entropy for the adsorption process were determined. The free energy of adsorption was in the range of – 38 to – 32 kJ mol 1 becoming more positive with the increase in temperature. The calculated enthalpy of adsorption was – 81.09 kJ mole-1 and the free entropy of adsorption was equal to – 127.88 J mole-1 K-1. The fundamental thermodynamic parameters reveal that mimosa tannin chemisorbs to the steel surface in a spontaneous, exothermic process that is accompanied by the decrease in entropy. The influence of specific adsorption adsorption of Cl- ions and of protonation of the adsorbate molecules was also considered. The results were explained in terms of chemical thermodynamics and the electronic molecular structure.

low carbon steel; mimosa tannin; weight loss; pickling; adsorption isotherm;

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