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There’s a reason we use diamonds as the benchmark for hardness. The sparkly gemstones have the highest confirmed Vickers hardness (VH) of any natural material at around 70 gigapascals (GPa) and they’re even named after the Greek word for “invincible”.
Well, we’re afraid that’s just not going to cut it anymore. Scientists in China have created a new form of carbon called AM-III, and it’s the hardest and strongest amorphous material known so far. With a VH of 113 GPa, it is quite literally harder than diamond – and about as strong.
“The materials exhibit outstanding mechanical properties – comparable to crystalline diamond, and the hardness and strength of AM-III surpass any known amorphous materials,” the researchers explained in their study, published last week in the journal National Science Review.
“The emergence of this type of ultrahard, ultrastrong, semiconducting [amorphous] carbon material offers excellent candidates [for] most demanding practical applications.”
Diamond owes much of its extraordinary strength and durability to its extremely regular structure – it consists only of single carbon atoms arranged in a tetrahedral structure. You might expect, therefore, for the new even-stronger material to have a similar structure – but you’d be completely wrong.
The team discovered AM-III by squashing buckyballs (a cage of 60 connected carbon atoms arranged kind of like a soccer ball) until they collapsed, resulting in the creation of an amorphous material – that’s what the AM in AM-III stands for. That makes it very unlike diamond indeed – in fact, it’s more like glass.
You may have heard the myth that glass is actually a liquid. It’s not, but it’s not exactly a solid either: it’s another one of these peculiar amorphous solids. What this means, for glass and for AM-III, is that the molecular structure has no long-term order to it – the molecules aren’t as disorganized as the chaos you’ll see in a liquid, but neither are they as regular and ordered as you find in a solid. That means that you end up with a material that is solid in every practical sense, but whose molecules can still actually move around over time – albeit a really, really, really long time.
One of the many suggested applications of AM-III uses this glass-like quality quite directly: it’s been suggested that the new material could be used to manufacture bulletproof windows that are 20 to 100 times tougher than current technology.
The amorphous quality of AM-III gives it a whole host of other properties, making it widely applicable in high-tech industries, the researchers say. For example, AM-III is also a pretty good semiconductor. That means there’s potential for the new material to be used for “novel photoelectric applications,” according to the researchers – think solar energy or space-age weapons.
While mass production of the new material is likely to take some time – and unlikely to be cheap – the wide variety of applications make this new yellow-tinted glass something we might see a lot of in the future.
“AM-III is indeed a new AM carbon material never detected and reported before,” explains the paper. “The distinct short-range order, microstructure and composition provide a unique combination of semiconducting and superior mechanical properties […] and calls-up for further experimental and theoretical exploration of the AM carbon allotropes.”
