Theoretical and experimental studies of the prevention mechanism of organic inhibitors on silver anti-tarnish

Organic inhibitors used for the anti-tarnish treatment of cyanide-free silver electrodeposit were investigated by both theoretical and experimental studies. The molecular properties of inhibitors, both orbital and electronic, for silver anti-tarnish treatment were studied using quantum chemical calculations based on density functional theory. Surface morphologies of the silver deposits with studied inhibitors and distribution of elements on silver deposits were characterized by field emission scanning electron microscopy (FESEM). All studied inhibitors used in this work can uniformly distribute on silver surfaces to form barrier layers. The inhibition effect of these inhibitors for silver anti-tarnish in 10 mM K₂S were revealed by Nyquist and Tafel plots measurements. Results of electrochemical measurements demonstrate that octadecanethiol was the most promising inhibitor for silver anti-tarnish treatment. The inhibition efficiency (η_p) of octadecanethiol for silver anti-tarnish in K₂S solution can reach 98.80%. The prevention mechanism of inhibitors on silver anti-tarnish treatment was further studied by molecular dynamic simulations, water contact angle measurement, appearance study, FESEM, and X-ray photoelectron spectroscopy measurements. With an effective adsorption of octadecanethiol, the silver becomes hydrophobic and avoids contact between silver and an aggressive K₂S medium, making octadecanethiol the most promising inhibitor for silver anti-tarnish treatment.