Bqd and L-Cys Synergistic Corrosion Inhibition on Mild Steel in Hedp-Acidic Environment

Abstract

The performance of corrosion inhibitors was investigated in a 363 K, 15% etidronic acid (HEDP) multi-hydrogen acid acidification system undergoing static weight loss tests. The results indicate that the corrosion inhibition rate of diploid benzyl quinoline quaternary ammonium chloride (BQD) is only 12.88% when used alone. When combined with L-cysteine (L-CYS), the corrosion inhibition rate can reach more than 95% when the total amount of corrosion inhibitor is only 0.05%. When the mass ratio of BQD to L-CYS is 1:1, the corrosion rate reaches its lowest value (1.66 g·m−2·h−1) and the corrosion inhibition rate attains its highest value (99.51%). Electrochemical tests show that BQD and L-CYS composite corrosion inhibitor system simultaneously slow down the cathode and anode reactions. The optimal mass ratio is 1:1, which is consistent with the results of static weightlessness. To validate the performance and understand the inhibition mechanism, a series of surface analyses were conducted: scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), contact angle measurements, molecular dynamics simulations, and quantum chemical calculations. These studies demonstrated that BQD and L-CYS synergistically formed a dense protective film on the N80 steel surface, making it hydrophobic and reducing direct contact between the acid solution and the metal, thereby lowering the corrosion reaction rate.

Keywords: Multi-hydrogen acid, etidronic acid (HEDP), BQD and L-CYS, N80 steel