Study of Anti-Tarnishing Mechanism in Ag-In Binary System by Using Semi-Quantum-Mechanical Approach

Tarnishing of silver objects have been real issues throughout millennia of human civilization history due to the fact that silver is very susceptible to sulfur element and can easily get tarnished by sulfur-containing gases. Over the past several decades, researchers have been studying mechanisms of tarnishing phenomena and tried to formulate and develop anti-tarnishing engineering solutions for various fields of applications, including jewelry, catalysts, electronics and optics. Recently, our research group demonstrated that silver-indium solid solutions possessed excellent anti-tarnishing property by quantitative experimental studies. However, the anti-tarnishing mechanism in silver-indium binary system is still unknown. In this paper, anti-tarnishing mechanism in silver-indium binary system is studied by a semi-quantum-mechanical approach. Silver-indium thin film were systematically examined by several experimental approaches in order to study their crystallography and surface properties thermodynamically. An original semi-quantum-mechanical approach was introduced for calculating the Hard and Soft Acids and Bases quantifiable parameters based on conceptual DFT formalization and incorporated with the Hammer-Nørskov d-band model, namely, absolute electronegativity and chemical hardness. Finally, the discovery of increasing absolute electronegativity and chemical hardness can be used to theoretically interpret the most fundamental mechanism behind the mystery of anti-tarnishing phenomenon in the silver-indium binary system.