Diamonds are famous for being the hardest natural substance on Earth, but they have a surprising weakness: They can crack or shatter when struck with enough force. Now, Chinese scientists say they have developed a new diamond composite that addresses that vulnerability, boosting diamond’s toughness by as much as six times while preserving its extraordinary hardness.
The breakthrough, reported in Nature Synthesis, comes from researchers at the Institute of Physics of the Chinese Academy of Sciences and Beihang University in Beijing. Their solution is surprisingly simple to picture: They created an internal network of microscopic carbon nanotubes that helps hold the diamond together when it comes under stress.
To understand why that matters, it helps to distinguish hardness from toughness. Hardness describes a material’s ability to resist scratching or indentation. Diamond ranks 10 on the Mohs scale, the highest possible rating. Toughness, by contrast, describes how well a material absorbs energy and resists cracking or breaking.
In other words, a diamond can shrug off a scratch but still be vulnerable to a sharp impact. Its rigid atomic structure contains directions of relative weakness, known as cleavage planes. A sufficiently forceful blow at the wrong angle can send a crack through the stone.
The Chinese researchers essentially gave the new diamond material a safety net — at a microscopic level.
They mixed diamond powder with multi-walled carbon nanotubes, extraordinarily thin carbon fibers that are many times stronger than steel. The mixture was then subjected to temperatures approaching 3,632 degrees Fahrenheit and pressures roughly 150,000 times greater than normal atmospheric pressure.
The extreme conditions caused the nanotubes and diamond particles to form strong bonds. The resulting three-dimensional network works somewhat like steel reinforcing bars inside concrete. When a crack begins to form, the nanotubes help redirect it, absorb energy and prevent it from spreading rapidly through the material.
Laboratory tests found that the diamond composite had a hardness of about 91.6 gigapascals — comparable to common single-crystal diamond — while its toughness improved up to sixfold, according to the researchers. The material was even reported to be tougher than tungsten alloys used in armor-piercing ammunition.
We don't expect these super-tough diamonds to start appearing in engagement rings anytime soon. The potential applications are decidedly more industrial than glamorous. The material could eventually be useful in heavy-duty cutting and polishing tools, geological drill bits and components designed to withstand extreme wear or demanding aerospace environments.
Credit: Fanciful image by The Jeweler Blog using aichatapp.ai.