Shiny new results from the Goldsmiths’ Company Charity Studentships in Precious Metals
Beyond advancing the understanding of precious metals for the jewellery industry, three PhD students in the Department of Materials Science and Metallurgy funded by the Goldsmiths’ Company Charity have generated research findings applicable in fields as diverse as textile production and biomedical implants.
We caught up with students Owain Houghton and Jamie Hogg, and Ayush Prasad’s supervisor, to hear more details of their respective research journeys.
Owain Houghton
Owain Houghton has been exploring specific properties of precious metal alloys—principally 18-karat gold, which is a minimum of 75% pure gold by mass—that can form a state called Bulk Metallic Glass (BMG). The name of ‘glass’ in this case means that the metal, when melted in such a way as to avoid crystallising into a highly ordered lattice arrangement of atoms, instead forms only local clusters of atoms without long-range order, giving it the structure of a liquid but the resistance to deformation of a solid. BMGs are of great interest to the jewellery industry for their hardness (and therefore scratch-resistance) and their ability to be formed by injection moulding for fast production of casts. In addition, BMG casts can take on high-definition surfaces and straight out of the mould represent the semi-finished state that requires no more than a polish before they are ready to be made into commercial items. Some zirconium-based BMGs are already used in bezels for luxury watches (James Bond sported one such in the film Spectre).
“The gold-based BMGs already in existence tarnished quickly”, explains Owain, “so my goal was to develop alloys that are tarnish-resistant”. To be useful industrially, Owain’s experimental alloys—with additions of copper, silicon, silver and palladium—had to contain enough gold to satisfy the specification of the hallmark while still retaining the properties of a glass. “We were successful, and we have filed a patent through Cambridge Enterprise as well as submitting several academic papers”, adds Owain. “It wouldn’t have been possible to research with these costly materials without Goldsmiths’ generous support. But most of all the contacts that Goldsmiths’ enabled, and the engagement at conferences I was supported to present at, gave me crucial insight into what people in the jewellery industry want to achieve”.
Having completed his PhD and now working at MIT in ‘the other Cambridge’ as a postdoc, Owain remembers his time in Cambridge fondly as “really special and so full of opportunities – Goldsmiths’ helped that”. He has also devised a website, Science of Jewelry: Noble metals explained simply, to encourage younger people in the jewellery industry to learn more about the fascinating science that underpins their everyday work.
Jamie Hogg
Jamie Hogg’s initial goal was to investigate the potential of gold-platinum alloys for making scratch-resistant jewellery. He found the only way to generate the required hardness was by mixing roughly equal quantities of the two precious metals, which then meant that the alloys were only compliant with low-karat (9k or 12k) hallmarks. Given that the mixtures were nominally 100% precious metal they may still have appeal for the jewellery industry, but gold-platinum alloys can be difficult to process as they have a narrow heat-treatment window (between the temperature at which they are soft enough to shape or drill, and the melting point).
Jamie next explored how the characteristics of the alloy changed when he added palladium metal to the mix, and the result was improved processability due to the widening of the heat-treatment window. “I was surprised that nobody had made similar mixtures before”, says Jamie, “where each metal was present at 20% or more of the composition”. Reading up on where gold-platinum alloys play a vital role in industry, Jamie identified a key component in the machinery that creates rayon fibres: the spinneret, a saucer-sized metal plate studded with thousands of tiny holes through which the fibres are extruded. “My alloy is stronger and easier to produce, which is an advantage for these delicately engineered components that are susceptible to damage and need frequent replacement,” he explains. There are several stages to creating the gold-platinum-palladium alloy—first mixing in an arc melter and then heating at two different temperatures—and Jamie found that the addition of palladium improved the homogenisation of the alloy during the first heat treatment, preventing unwanted melting of the gold-rich regions. This trick may prove useful in the many other applications of similar alloys, from dentistry to medicine.
Ayush Prasad
Ayush Prasad, meanwhile, has studied titanium-niobium alloys, which are the basis of superconducting magnets for magnetic resonance imaging machines, and used in actuators for the aerospace industry and hard-tissue implants in medicine. These alloys can exhibit shape memory or ‘superelastic’ behaviours, changing their structure dynamically and reversibly in response to their environment. “There was a gap in the scientific literature about the impact of incorporating precious metals into these alloys,” explains Professor Nick Jones, who supervises Ayush. “We were curious about whether introducing gold, silver or platinum would produce interesting new characteristics, and we found that adding gold led to an alloy with a lower elastic modulus, meaning that it was less stiff.”
This finding has led the team to explore potential uses for bone implants, such as ball-and-socket hip joints. The ideal implant is one that matches the properties of the surrounding bone very closely but the titanium alloys currently in use are three to four times more rigid, which the body interprets as a signal that the bones do not need maintaining at their former level. After many years, the bones holding the implant have shrunk, preventing the joint from working properly, and a new implant is required. Inserting an implant that is a bit less stiff could circumvent this problem and now the team is also exploring if the alloys containing gold have antibacterial properties, which would be an added bonus for successful implantation. “Without the Goldsmiths’ Company Charity’s impetus to study precious metals, and their funding for Ayush, we might never have come up with these important findings and crossed disciplines from aerospace to biomedicine,” said Professor Jones.
“The Goldsmiths’ Company Charity would like to congratulate Owain, Jamie and Ayush on their exceptional research findings. Funding studentships in precious metals aligns with the charity’s ambitions to support the ‘development of creative, design, craft, and scientific skills in goldsmithing, silversmithing, jewellery, and allied trades’ and we are pleased with the progress that has been made through these three research programmes.”