Corrosion inhibition and adsorption studies of Ammonium oxalate for mild steel by computational and experimental techniques: A sustainable approach

Abstract

• AO was tested as corrosion inhibitor for mild steel in 0.5 M HCl. • Gravimetric, polarization, impedance, metallurgical, DFT, LAI methods were used. • AO was proved to be very good anti-cracking and anti-pitting agent. • AO shows 94.94% corrosion inhibition efficiency for mild steel. • BOD and COD of wastewater was found to be within the permissible limits. The exact mechanism of inhibition and adsorption is very essential for designing acid corrosion inhibitors. So far sincere efforts are lacking in explaining the exact mechanism of adsorption and corrosion inhibition for acid corrosion inhibitors. Ammonium oxalate (AO) was investigated as a highly efficient corrosion inhibitor for mild steel in 0.5 M HCl by different theoretical and experimental methods. Experimental methods like gravimetric, impedance, polarization, and metallurgical microscopy were supported by theoretical techniques like DFT, MD simulation, Frontier molecular orbital, and adsorption isotherm studies. Surface studies like the morphology of corroded specimens, nature, and type of corrosion were carried out by metallurgical microscopy technique. Different chemical interaction parameters (global reactivity parameters) between the inhibitor and mild steel provide sufficient information about the adsorption and inhibition mechanism shown by AO for mild steel. A linear correlation regression coefficient was observed between AO concentration and inhibition efficiency. A maximum of 94.94% inhibition efficiency was observed at a 1000 ppm concentration of AO. The polarization study shows that AO act as a mixed inhibitor. Impedance study proves that an increase in AO concentration leads to an increase in charge transfer resistance and hence barrier film thickness. The length of pores, percentage porosity, and intensity of cracks decreases appreciably after the addition of 100 ppm of AO. The biochemical assay of waste acid after gravimetric experiments was observed to be within permissible limits. Ammonium oxalate (AO) was investigated as a highly efficient corrosion inhibitor for mild steel in 0.5 M HCl by different theoretical and experimental methods. Experimental methods like gravimetric, impedance, polarization, and metallurgical microscopy were supported by theoretical techniques like DFT, MD simulation, Frontier molecular orbital, and adsorption isotherm studies. Surface studies like the morphology of corroded specimens, nature, and type of corrosion were carried out by metallurgical microscopy technique. Different chemical interaction parameters (global reactivity parameters) between the inhibitor and mild steel provide sufficient information about the adsorption and inhibition mechanism shown by AO for mild steel. A linear correlation regression coefficient was observed between AO concentration and inhibition efficiency. A maximum of 94.94% inhibition efficiency was observed at a 1000 ppm concentration of AO. The polarization study shows that AO act as a mixed inhibitor. Impedance study proves that an increase in AO concentration leads to an increase in charge transfer resistance and hence barrier film thickness. The length of pores, percentage porosity, and intensity of cracks decreases appreciably after the addition of 100 ppm of AO. The biochemical assay of waste acid after gravimetric experiments was observed to be within permissible limits.