Experimental and computational evaluation of poly(aspartic acid-co-melamine) for efficient corrosion inhibition of carbon steel in saline acidic environments

Corrosion of carbon steel in saline-acidic environments severely compromises oil-field and industrial assets. Here, a melamine-grafted poly(aspartic acid) copolymer (PSAM) is synthesized and shown to form a compact, adherent protective film on C1018 steel in 1 M HCl–3.5 % NaCl. Structural analyses (FTIR, ¹H NMR) confirm successful grafting. Weight-loss and electrochemical measurements reveal a substantial decrease in corrosion activity, with inhibition efficiency exceeding 93 % at 200 ppm. PSAM decreased the corrosion rate of C1018 steel in the blank from 10.8 to 0.785 mm/yr at 200 ppm and increased the polarization resistance (Rp) from 12 to 148 Ω cm² respectively. Potentiodynamic polarization indicates mixed-type inhibition, suppressing both anodic dissolution and cathodic hydrogen evolution. Impedance results show enhanced charge-transfer resistance and reduced double-layer capacitance, consistent with stable surface coverage. SEM images demonstrate a much smoother, less damaged steel surface in the presence of PSAM, while EDX shows markedly lower oxygen and chloride content, confirming reduced corrosion-product formation. Complementary DFT calculations indicate strong electron-donor capability and favorable adsorption interactions between PSAM and iron, supporting an adsorption-driven mechanism. These findings demonstrate that PSAM provides high-efficiency, environmentally compatible protection under aggressive saline–acidic conditions, highlighting its potential for oil-field and industrial applications.