Investigation of phosphorous organic compounds adsorption during corrosion inhibition of copper alloys into simulated seawater

• A cyclic phosphonium salt tested for corrosion control on copper alloys. • Experimental setup optimized using response surface methodology. • Strong inhibition performance observed, especially on pure copper. • Microscopy showed surface protection layers on most tested metals. • Adsorption process matched chemisorption and multilayer behavior. This work explores the protective behavior of a cyclic phosphonium salt (PBC) when applied to various copper-based metal surfaces, including Cu, CuZn, CuSn, and CuNi. A central composite design (CCD) approach was employed to fine-tune the experimental conditions, identifying 77 minutes of immersion, a concentration of 6 µg/L, and a temperature of 298 K as optimal. Tafel polarization measurements demonstrated that PBC effectively inhibits corrosion, with efficiencies ranging from 85 % for Cu to 34 % for CuNi. Scanning electron microscopy confirmed the formation of a surface film on most substrates, with CuNi being the least responsive. These findings suggest that PBC has promising potential as a selective and efficient corrosion inhibitor, particularly on copper-dominant alloys. Kinetic fitting revealed a pseudo-second-order profile, suggesting chemisorption as the governing process, while adsorption data aligned with the Freundlich model, indicating multilayer deposition on heterogeneous surfaces. Finally, a detailed mechanism for corrosion inhibition through an adsorption process has been proposed and thoroughly elucidated.