Abstract
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.
Highlights
Silver was used for coins in ancient Lydia around 700 BC,[1] but still finds new special niches of technological applications, such as silver thin films,[2,3,4] silver nano-particles,[5,6,7,8,9] and silver nano-sintering.[10,11] It possesses superior material properties, such as the highest electrical conductivity of any element, the highest thermal conductivity and reflectivity among metals, reasonable price and truly remarkable aesthetic value
The experimental results showed that silver-indium solid solutions exhibited a superior anti-tarnishing property, which could be meaningful to various fields of silver applications, such as jewelry, catalyst, welding, electronics, and optics
With the scientific knowledge of anti-tarnishing mechanism, it could serve as a design guidance in principle for the practical applications of Ag-In alloy bulk or thin film materials into various fields, such as electrical and mechanical interconnections of SiC/GaN-based power electronics, GaN-based LED reflector, giant astronomical telescope array of mirrors construction etc
Summary
Journal of The Electrochemical Society, 164 (7) C418-C427 (2017) 0013-4651/2017/164(7)/C418/10/$37.00 © The Electrochemical Society. In order to search possible scientific and engineering anti-tarnishing solutions, some surface treatment techniques for silver have been proposed, using different coating methods or coating materials, such as metallic coating by electroplating,[21] sputter-applied coatings,[22] oxide coating,[23] organic coating,[24] chromate conversion coating.[25] such thin layers of coating material can be worn out very after a period of time. Another approach to address tarnishing issues for silver is by alloying. A physical-chemical model is proposed to explain the anti-tarnishing mechanism in the silver-indium binary system, based on experimental evidence and self-contained theoretical analysis
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