Kinetic and thermodynamic evaluation by weight loss and FTIR techniques of CAFFEINE as anticorrosion for TIN in acidic and alkaline media
Keywords:Corrosion, Caffeine, Tin, FTIR, Weight loss, HCl, NaOH
The corrosion behaviour of Tin in hydrochloric acid and sodium hydroxide solutions using weight loss and FTIR techniques was investigated to test the effect of contact time, corrodent concentration and temperature variation. The inhibition efficiency of tin in each media by using the caffeine sample was found at optimum inhibitor concentration (0.5%) to be 77.78% at 30 0C and 71.43% at 50 0C in the acidic media while in the basic media it gives a maximum efficiency of 54.55% at 30 0C and 44.83% at 50 0C which the overall results obtained showed that the caffeine has good performance in the acidic media and could be used to prevent the corrosion of the metal in the acidic media. At lower concentration of 0.1%, the inhibition efficiency was found to be 29.63% at 30 0C and 22.86% at 50 0C in acidic media while it gives 22.73% at 30 0C and 13.79% at 50 0C in basic media. This revealed that the inhibition efficiency decreased with increased in temperature but increased with increasing inhibitor concentrations. The research also includes determination of activation energy, Gibbs free energy whose values are 20.738, 19.075 kJmol-1, -2.488, -1.047 kJmol-1 in acidic and alkaline media respectively. The adsorption was found to obey Freundlich isotherm with linear coefficient (R2) and equilibrium parameter (Kads) to be 0.0455, 0.0266 for both systems in acidic and alkaline media respectively. Physical adsorption mechanism is proposed from the trend of DGads. The negative values of DGads show the spontaneity of the inhibition process. The increase in the activation energy of the inhibition processes with values less than the threshold value of 80 kJ/mol support the mechanism of physical adsorption process.
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