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When it comes to metallurgy, it is common knowledge that smaller grains produce harder metals. But how exactly do you get these grains?
A group of researchers at Brown University have found a method to break down individual metal nanoclusters that lead to metals that are up to four times harder than natural structures. This new method is quite different from conventional hardening techniques.
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“Hammering and other hardening methods are all top-down ways of changing grain structure, and it’s very difficult to control what grain size you end up with,” Ou Chen said in a press release, assistant professor of chemistry at Brown and corresponding author of the new research.
“What we’ve done is create building blocks of nanoparticles that fuse together when you squeeze them. This way we can have uniform grain sizes which can be fine tuned for improved properties.
For this research, the team used nanoparticles of gold, silver, palladium, and other metals and chemically stripped them of organic molecules called ligands, which typically prevent metal-to-metal bonds from forming between particles. . The clusters were then able to merge with just a little pressure.
New metal parts made with this technique were found to have almost identical electrical conduction and light reflectance to standard metals, but their optical properties were radically altered.
“Due to what’s called the plasmonic effect, the gold nanoparticles are actually purplish-black in color,” Chen said. “But when we apply pressure, we see those purplish clusters suddenly turning to a brilliant gold color. This is one of the ways we knew we had actually formed loose gold.
Researchers are now looking to apply the technique to commercial products because the chemical treatment is relatively simple to perform. Chen has currently patented the technique and sees great potential “for both industry and the scientific research community.”
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