Enalapril maleate as a green accelerator for zinc phosphating coating on low-carbon steel

In this study, enalapril maleate (EM), a green ingredient of an antihypertensive drug, was selected as an accelerator for phosphate coating promoting on low-carbon steel. The scanning electron microscope (SEM), X-ray diffraction (XRD), 3D morphologies, coating weight, coating thickness and free acidity (FA) as well as total acidity (TA) were characterized to analyze the coating performance. Copper sulfate titration, potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) were performed to evaluate corrosion resistance of phosphate coatings. The DFT computations were applied to explore the phosphating promoting mechanism. The results show that the EM optimal concentration is 1.6 g/L which lowers the operating temperature (form 80 celcius to 40 celcius), generates the smoothest (Ra = 2. 85 lm), the heaviest (28.35 g/cm2) and the thinnest (21.6 lm) coating, and reduces the corrosion rate from 1.099 mpy of blank to 0.0246 mpy. The density functional theory (DFT) results confirm that EM adsorbs on low-carbon steel by electrophilic sites (N10) as well as nucleophilic sites (C10), forms nucle-ated particles preferentially and accelerates the growth of crystals. Therefore, EM is a green organic com-pound with high phosphating promotion efficiency which has potential application prospects in industrial phosphating.(c) 2023 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.