More wear resistance with graphene gilding
Adding a single layer of graphene to metal films used to gild precious artefacts, increases wear resistance. Idha Valeur reports.
Adding a 2D layer of graphene to precious artefacts, through a supplementary second step to the original gilding process, could help protect and increase the wear resistance of anything from ship hulls to jewellery and electronics. This additional step is also very cost efficient as the amount of graphene needed to cover any item that requires gilding is microscopic.
Sameh Tawfick, Assistant Professor from the Department of Mechanical Science & Engineering and the Beckman Institute, part of the University of Illinois College of Engineering, USA, was inspired by the gilding process used by ancient Egyptians and Chinese, of coating artefacts in thin metal films, making them resistant to corrosion, wear and degradation caused by environmental factors.
The engineers outlined that adding a layer of graphene on top of thin metal leaves of palladium will double the protection against wear and tear, in their study, Gilding with graphene: rapid chemical vapor deposition synthesis of graphene on thin metal leaves, published in Advanced Functional Materials.
Tawfick told Materials World, ‘Graphene is an atomically thin material, that is also the strongest material humans know. Also, carbon is a very light material. It is stable when it is atomically thin, which means it has a big effect without changing the optical properties.’
Metal leaves are easily accessible, being available to purchase in large rolls at a low price, and Tawfick and his team were able to increase resistance by bonding a layer of graphene to these leaves.
‘Adding one more layer of graphene atoms onto the palladium made it twice as resistant to indents than the bare leaves alone. It’s also very attractive from a cost perspective. The amount of graphene needed to cover the gilded structures of the Carbide & Carbon Building in Chicago, for example, would be the size of the head of a pin,’ Tawfick said.
In addition to finding a cost effective, easily applied and stronger layer for gilding, the engineers also developed a technology that would enable them to grow high-quality graphene directly on the surface of 150 nanometre thin palladium leaves in 30 seconds. By using chemical vapour deposition (CVD), where the metal leaf is processed in a 1,100°C furnace, the leaf acts as a catalyst, making the gases able to react quickly.
Tawfick said, ‘CVD is a process where gases are transformed into solid deposits at high temperatures, and in this case low pressure. The unique aspect of CVD is that it deposits graphene on the metal leaves, creating a very intimate interface between them, and good bonding. It is very hard and expensive to get single layers of graphene and deposit them manually on the metal leaves. And even if successful, the interface will be dirty. Graphene is an atomic layer, so you need to think about it differently.’
The team’s findings highlight new opportunities for coating larger structures, such as buildings, ship hulls, and metal surfaces of electronics, and smaller precious artefacts or jewellery.
Tawfick explained that there are no big obstacles for this method to reach industrial scale, as the gilding process will remain largely the same. The only change would be creating an additional step to the production of the leaves – adding the graphene through the vapor deposition process. Going forward, Tawfick wants to learn about other potential benefits of graphene when added to metal leaves, such as how it may enhance other properties, like friction.