China scientists create crystal stronger than diamond

Chinese researchers have developed a diamond composite that integrates a network of multi-walled carbon nanotubes (MWCNTs) to enhance fracture resistance while maintaining high hardness. Published in the journal Nature Synthesis, the study reports an average fracture toughness of 31.9 MPa m¹ᐟ², approximately five times that of single-crystal diamond.

The research team, affiliated with the Institute of Physics of the Chinese Academy of Sciences and Beihang University, achieved a hardness of about 91.6 GPa for the composite. This approach aims to improve diamond's fracture resistance without compromising its hardness, a common trade-off in material science.

The diamond composite was synthesized under high-pressure, high-temperature conditions, with experiments conducted at 2,000°C and 15 GPa. The study highlights the role of MWCNTs in forming a three-dimensional network that helps dissipate energy and impede crack propagation through the diamond matrix.

The interfaces between the nanotube network and the diamond grains feature mixed sp²-sp³ carbon bonding, crucial for enhancing the material's toughness. The researchers also constructed a three-dimensional diamond framework to maintain strong diamond-to-diamond bonding, preventing a significant loss of hardness.

This development could be relevant for advanced cutting tools and components where both wear resistance and resistance to cracking are critical. However, the study does not confirm the material's readiness for commercial production or large-scale industrial use.

In a related study published in March in Nature, researchers from Zhengzhou University, Nanjing University, and Henan University of Science and Technology synthesized millimeter-sized, phase-pure hexagonal diamond. This material, produced from highly oriented pyrolytic graphite, showed slightly higher hardness than conventional cubic diamond and high thermal stability.

The two studies highlight different strategies for enhancing diamond-based materials: reinforcing conventional diamond with carbon nanotubes to resist cracking and creating a new carbon crystal structure with potentially different mechanical properties. Further research is needed to assess the industrial viability of these materials.