Silver Tarnishing Mechanism Revealed by Molecular Dynamics Simulations.

The mechanism of silver-oxygen and silver-sulfur reactions is revealed by means of molecular dynamics simulations, performed with reactive force fields purposely built and extensively tested against quantum-chemical results. Different reaction mechanisms and rates for Ag-O and Ag-S emerge. This study solves the long-lasting question why silver exposed to the environment is strongly vulnerable to sulfur corrosion (tarnishing) but hardly reacts with O2 , despite the thermodynamic prediction that both oxide and sulfide should form. The reliability of the simulation results is confirmed by the agreement with a multitude of experimental results from the literature.