In a new experiment, researchers from Brown University have created nanoparticles which help create super-hard metals. Traditional ways of hardening metal include many methods like bending, twisting, hammering, etc. These methods focus on breaking up the metal’s grain structure.
The new study has found an alternative method to work on these metallic grain structures at the nanometer scale.
The report “Bulk Grain-Boundary Materials” from Nanocrystals recently appeared in the journal Chem, January 22.
The new result shows the metal is harder by four times the naturally occurring metal structures. By smashing individual metal nanoclusters and using them to form harder and larger scale pieces of solid metal, they could make the metal harder.
Ou Chen, the corresponding author in the study and a chemistry assistant professor at Brown, said that Hammering and other hardening methods are all top-down ways of altering grain structure, and it’s tough to control the grain size you end up with.
He explains that their method creates “nanoparticle building blocks” which are squeezed to fuse in order to create uniform grain sizes. These microscopic pieces of the metal can now be controlled and used precisely to achieve improved results.
Researchers created centimetre-scale “coins” from metallic nanoparticles – gold, palladium, silver, and more. These items of the size of a coin are useful in many places like electrodes, thermoelectric generators and many more. It is believed that this method can be used even further for industrial parts of super-hard metal coating materials.
Chen added that the key point here is in the chemical treatment of the nanoparticle grains. Ligands which are organic molecules that bond to a central metallic atom and prevent metal to metal bonding were used. These ligands were stripped, thus allowing the clusters to bond together with enough pressure resulting in harder metal coins.
The optical properties of gold coins which were created in the study were “fascinating,” noting a colour change when the nanoparticles were squeezed to create the metal coins. The phenomenon is called the plasmonic effect. This describes the interaction between free electrons and light. They also noted that gold nanoparticles are actually purplish-black but turn into bright gold on applying pressure.
This technique can be used on any metal.
“Making metallic glass from a single component is notoriously hard to do, so most metallic glasses are alloys,” Chen added. Starting with amorphous palladium nanoparticles, researchers could create a palladium metallic glass.
Yasutaka Nagaoka, Masayuki Suda, Insun Yoon, Na Chen, Hanjun Yang, Yuzi Liu, Brendan A. Anzures, Stephen W. Parman, Zhongwu Wang, Michael Grünwald, Hiroshi M. Yamamoto, Ou Chen. Bulk Grain-Boundary Materials from Nanocrystals. Chem, 2021; DOI: 10.1016/j.chempr.2020.12.026
Press Release: Brown University