When it comes to metallurgy, it is well known that smaller grains yield harder metals. But how exactly do you reach these grains?
A group of researchers from Brown University has found a method to smash individual metal nanoclusters that leads to metals that are up to four times harder than naturally occurring structures. This new method is very different from conventional hardening techniques.
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“Hammering and other hardening methods are all top-down ways to change grain structure, and it’s very difficult to control the grain size you get,” said Ou Chen, an assistant professor of chemistry at Brown and the corresponding author of the novel. research.
“What we’ve done is make nanoparticle building blocks that fuse together when you squeeze them. In this way we can have uniform grain sizes that can be fine-tuned for improved properties. “
For this study, the team used nanoparticles of gold, silver, palladium, and other metals and chemically removed them from the organic molecules called ligands, which generally prevent metal-metal bonds from forming between particles. The clusters were then able to merge with a little pressure.
The new metal coins made with the technique were found to have electrical conductivity and light reflection almost identical to standard metals, but their optical properties had changed drastically.
“Because of what is known as the plasmonic effect, gold nanoparticles are actually purplish-black in color,” Chen said. “But when we applied pressure, we suddenly see these purplish clusters turn a bright golden color. That’s one of the ways we knew we had actually formed bulk gold. “
The researchers are now trying to apply the technique to commercial products, as the chemical treatment is relatively easy to perform. Chen currently has the technique patented and sees great potential for “both for industry and for the scientific research community”.