DFT and electrochemical studies of new superplasticizers on the corrosion inhibition of 316L stainless steel in neutral medium: A comparative study

Abstract

In this study, new corrosion inhibitors such as polycarboxylate ether (PCE), sulfonated naphthalene formaldehyde (SNF), modified lignosulphonate (MLS), and sulfonated melamine formaldehyde (SMF) are utilized for 316L stainless steel in a 3.5% NaCl medium. ATR-IR and UV–Vis spectroscopy were used to study the superplasticizers' structural characterization. Based on the ATR-IR and UV–Vis results, all of the spectrum information for PCE, SNF, MLS, and SMF are closely matched to the findings of the significant superplasticizers described in the literature. Electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP) measurements and the weight loss method were used to investigate the corrosion inhibition efficacy of new superplasticizers on 316L stainless steel in a 3.5% NaCl solution. According to the EIS, PDP, and weight loss results, SMF has the highest inhibitory efficiency of all the inhibitors examined. These could be attributed to the presence of additional heteroatoms (N, O, and S) in the SMF than in the other three inhibitors. The inhibition efficiencies were in the order of SMF > MLS > SNF > PCE, with the maximum inhibition efficiency of 88.8% for the SMF inhibitor at 0.00012 mol L−1 concentration. The adsorption of all inhibitors, including PCE, SNF, MLS, and SMF, is well-fitted and follows the Langmuir isotherm model. SEM and EDX analyses were used to study the corrosion mechanism of the adsorbed inhibitor molecules PCE, SNF, MLS, and SMF and their elemental composition on the metal surface. The SEM and EDX result reveals that the SMF inhibitor is substantially adsorbed onto the 316L SS surface as a protective layer. Quantum chemical calculations were utilized to give further evidence of the mechanism of inhibition action of all corrosion inhibitors such as PCE, SNF, MLS, and SMF. All the DFT studies demonstrate that sulfonated melamine formaldehyde (SMF) has outstanding inhibitory capabilities on 316L stainless steel in a 3.5% NaCl solution at room temperature out of the four proficient superplasticizers studied.