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Zhang Tong

Chinese scientists have created a diamond with no Achilles’ heel – one that cannot be broken, even by a hard knock with a hammer – according to a paper published in the peer-reviewed journal Nature Synthesis.
While a diamond is the hardest natural material on Earth, it has a major weakness. It is brittle, like glass, and a sharp blow can shatter it. For years, scientists have tried to make diamonds tougher without losing their legendary hardness.
Typically, increasing one characteristic has meant sacrificing the other – seen as a reasonable trade-off for most applications, which include industrial uses such as in cutting and polishing tools.
The team – from the Institute of Physics at the Chinese Academy of Sciences and Beihang University – found a way around this limitation, building an internal support structure to boost a diamond’s toughness by six times while leaving its hardness unchanged.
The breakthrough material is even tougher than the tungsten alloys used in armour-piercing ammunition, according to the paper, which was published online on July 9.


The secret lies in multi-walled carbon nanotubes (MWCNT) – ultra-strong carbon fibre “cords” that are incredibly thin, about one 10,000th of the width of a human hair, yet dozens of times stronger than steel, the paper said.
Earlier attempts to incorporate carbon nanotubes into ceramics or metals did not work well. The problem was that the MWCNT and the base material made only loose physical contact, so they could not effectively transfer force or share the load.
The Chinese researchers took a different approach, which started with them thoroughly blending the microscopic diamond powder needed to make the nanotubes.
Next, they subjected the mixture to extreme heat and pressure – 2,000 degrees Celsius (3,632 degrees Fahrenheit) and 15 gigapascals (GPa), which is about 150,000 times normal atmospheric pressure.
The pressure was chosen carefully: high enough to fuse the materials together, but not too high that it would turn the carbon nanotubes into diamond, nor so low that the powder became graphite.
The result was an array of nanotubes that kept their fibrous shape while forming strong chemical bonds with the diamond at the atomic level.
According to the paper, the nanotubes work like the rebar in reinforced concrete, forming a continuous 3D network between the diamond grains, which at the same time are bonding directly to each other.
Laboratory testing showed the new composite had a hardness of about 91.6 GPa – on par with an ordinary single-crystal diamond – and a toughness of up to 36.4 MPa.m1/2, a five to sixfold improvement that surpasses typical tungsten alloys, it said.
Potential uses
The scientists used an electron microscope to observe how cracks spread inside the material when it was stretched. In a regular diamond, cracks shoot straight through the material in a brittle fashion, much like glass breaking.
However, in the composite material, the nanotubes deflected and diverted the cracking, the researchers found. Countless nanotube “ropes” pulled on the crack from all directions, absorbing vast amounts of energy and stopping it from running wild.
Potential uses for the material are extremely broad, from super-hard cutting tools for machining metals and ceramics to geological drill bits and aerospace components.
The research work is supported by the national Synergetic Extreme Condition User Facility in Huairou Science City, Beijing, built to let scientists test materials under extreme environments.
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Scientists use carbon nanotubes to build an internal support structure that overcomes the brittle glasslike nature of diamonds


Scientists use carbon nanotubes to build an internal support structure that overcomes the brittle glasslike nature of diamonds.


Chinese Academy of Social Sciences

Tougher than armour, hard as diamond: China’s unbreakable crystal breakthrough

.css-1c6uqr6{color:inherit;font-weight:inherit;font-size:inherit;font-family:inherit;line-height:inherit;overflow-wrap:break-word;}Scientists use carbon nanotubes to build an internal support structure that overcomes the brittle glasslike nature of diamonds

Scientists use carbon nanotubes to build an internal support structure that overcomes the brittle glasslike nature of diamonds