Evaluation of the Modified Extracted Lignin from Wheat Straw as Corrosion Inhibitors for Aluminum in Alkaline Solution

摘要

Extracted lignin from soda pulping of wheat straw agricultural waste is modified and characterizedusing spectroscopic and thermal analysis. Modified lignin compounds (LG-OH & LG-COOH) areinvestigated as corrosion inhibitors for aluminum in 1.0 M NaOH compared to their unmodified lignin(LG) using potentiodynamic polarization measurements and morphological characterization. Datashow that the modified lignin compounds shift both the corrosion and the open circuit potentials ofaluminum to more noble values as well as decrease its corrosion current density (Icorr) compared to itsvalues in blank solution. The maximum inhibition efficiency is found to be in case of LG-COOHfollowed by LG-OH compared to LG. The higher inhibition efficiency of LG-COOH can be explainedto its higher active adsorption sites compared to LG-OH and LG. Adsorption of modified lignincompounds on aluminum surface is confirmed using SEM–EDX analysis. The best fit adsorptionisotherm is found to be Langmuir adsorption isotherm with physical nature. Thermodynamicparameters indicate endothermic nature of the corrosion process with higher ordered activatedcomplexes in the presence of lignin compounds.