Uncovering The Secrets Of The World’s Toughest Materials

Hexagonal boron nitride’s (h-BN) exceptional toughness comes from its unique structure and composition, helping the material withstand greater stress.

AsianScientist (Jun. 29, 2021) – A joint team of scientists from Singapore and the US has finally uncovered the key to the extraordinary strength of hexagonal boron nitride (h-BN), said to be one of the toughest materials on Earth. Their findings are described in Nature.

Believe it or not, but hidden in the eyeshadows and powders that makeup enthusiasts use daily is one of the world’s toughest materials—a two-dimensional (2D) structure just one atom thick called h-BN.

First used in makeup in the 1940s, h-BN is currently used by nearly all leading cosmetics companies for its ability to absorb excess facial oil and disperse pigment evenly. Outside the realm of beauty, h-BN is also used in electronics as an insulator, being able to withstand temperatures of up to 1000°C.

In an attempt to decode the secret to h-BN’s toughness, researchers from the Nanyang Technological University, Singapore (NTU) and Rice University examined breakages in samples of h-BN exposed to stress.

They found that breakages in h-BN branched much like forks in a road, meaning that fractures are less likely to grow if further stress is applied. In contrast, breakages tend to travel straight like a zipper in the case of graphene—another material considered to be one of the toughest on Earth—causing it to break off more easily.

As h-BN and graphene share the same honeycomb-like structure, the authors hypothesized that differences in composition could impact the materials’ ability to absorb stress.

After all, the hexagons in graphene consist solely of carbon atoms, whereas each hexagon structure in h-BN consists of three nitrogen and three boron atoms. True enough, this difference in composition is what causes cracks in h-BN to branch off, with subsequent cracks requiring more energy to form.

According to the authors, h-BN’s surprising toughness could make it ideal for producing tear-resistant flexible electronics, like wearable medical devices and foldable smartphones. It can also be used to strengthen electronics made from 2D materials, which tend to be brittle. Ultimately, the team’s study on h-BN’s unique properties could pave the way for new flexible materials in electronics.

“Our experiments show that h-BN is the toughest nanomaterial measured to date. What makes this work so exciting is that it unveils an intrinsic toughening mechanism in this material—which should be brittle as it is only one atom thick. This is unexpected as there is often a trade-off between the strength and brittleness of nanomaterials,” concluded lead author Professor Gao Huajian from NTU.

The article can be found at: Yang et al. (2021) Intrinsic toughening and stable crack propagation in hexagonal boron nitride.


Source: Nanyang Technological University.
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