In an inspiring collaboration, Prof. G S Vinod Kumar and Prof. Sheela Singh from the Department of Mechanical Engineering, Prof. Ranjit Thapa from the Department of Physics, and Dr Rajapandiyan Panneerselvam from the Department of Chemistry at SRM University – AP, along with PhD scholars Ms Harsha K and Ms Arunima J, have co-authored a compelling paper titled “Innovative Approaches to Enhancing the Tarnish Resistance of Silver Alloys.” This groundbreaking research focuses on developing new silver alloys that resist tarnishing, enhancing durability and aesthetic appeal for applications in the jewellery industry. Together, they are paving the way for innovative solutions that blend science with artistry.
Abstract
Silver and its alloys undergo tarnishing with time, which is a black stain on the surface due to the formation of Ag2S. Developing a tarnish resistant Ag alloy was attempted by alloying Ag with elements that form a passive oxide layer on the surface. Germanium is proven to provide better tarnish resistance to sterling silver alloy (92.5wt.% pure) which is available under the trade name of Argentium©. The present work investigates the tarnish resistance behaviour of sterling silver alloy (92.5wt.% pure) containing various additions of Copper, Zinc, Germanium, Aluminium, Beryllium, Titanium, Zirconium, and Magnesium. The alloys were prepared by melting and casting route, followed by Passivation Heat Treatment (PHT) to create a stable and continuous oxide layer. The temperature for PHT was optimized using thermogravimetry analysis (TGA) of the alloys prepared. An accelerated tarnish test was carried out to investigate the tarnishing behaviour of alloy samples obtained before and after PHT. The samples were characterized using XRD, SEM-EDX, TG-DSC, micro-Raman Spectroscopy, and XPS. The change in reflectance of the samples after the tarnish test is determined using UV-visible reflectance spectroscopy. The mechanism behind the tarnish resistance was derived using Density Functional Theory (DFT) by comparing sulphur (S2) and Oxygen (O2) adsorption energies (BE) of the alloying elements.
Explanation of the Research in layperson’s terms
Age-old silver pieces are found in different colours ranging from light yellow(silver Jewellery pieces after a few weeks of usage) to black(archaeological silver pieces). They look different in terms of the metallic white colour and lustrous appearance from fresh silver. This demeans silver and thus affects its market. The major cause of the staining of silver is the interaction of individual silver particles with some elements found common in the atmosphere. We work on the prevention of this staining of silver. For the study, silver is incorporated with other elements which makes silver less interacting with staining elements in the atmosphere. These additional elements create a layer over silver so that it is protected. The appropriate elements are identified by using modelling using computer software. After obtaining appropriate elements, the experimental trials are also done with the same elements until stainless silver is obtained. Then, what happens to the added elements inside silver is also studied by using modern microscopic technics.
Practical/Social Implications of the Research
The major application of the invention is in the jewellery industry. The problem of tarnishing is an age-old threat in jewellery making. The alloys we proposed could be used to make quality silver jewellery/articles that can sustain the colour and lustre for a longer period. This will stop the hesitation from jewellery designers and industries to try intricate designs in silver and find a better market for them. The alloys based on the proposed composition show good grain refinement and thus high hardness. This strengthens the soft silver and improves the range of its applications from low hardness articles to high. The alloys based on the proposed composition have high tensile strength. They deform plastically for a wide range of stress values and will not break easily.
Collaborations:
Waman Hari Pethe & Sons Jewellery
Future Research Plans:
1. Corrosion studies of silver alloys to understand the behaviour in solutions having compositions similar to that of sweat.
2. Study of mechanical properties of silver alloys to develop workable alloys of sterling silver which could be used for jewellery manufacturing
3. Identification of elements having better oxide layer formation when alloyed with silver, by using computational techniques and experimental studies of their properties.
Link to the article:
https://www.sciencedirect.com/science/article/pii/S2238785424024633