Hexagonal Boron Nitride is 10 Times Stronger Than Graphene
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The African Development Bank will finance $25 billion by 2025 to support Africa's fight against climate change, the bank's president said at the bank's annual meeting in Accra, Ghana.
He noted that climate change has had many negative impacts on the continent, causing natural disasters such as droughts, cyclones, and floods. Climate change costs Africa between $7 billion and $15 billion a year. "Africa has no choice but to address climate change."
To ensure Africa's food supply, the African Development Bank has delivered climate-friendly seeds to 12 million farmers in 27 countries in the past two years under the "Technology for Agricultural Change in Africa" program, he said.
In the area of renewable energy, the African Development Bank is implementing a $20 billion "Desert Power" initiative in the Sahel that is expected to power 250 million people, he said.
US President Joe Biden recently wrapped up his five-day trip to Asia with a summit of leaders of the "Quad" security Dialogue.
Biden has promoted a number of economic and security cooperation initiatives during his visit aimed at deepening ties with Indo-Pacific Allies and partners in response to China's growing influence in the region. Some analysts in the United States believe the most significant announcement may be an initiative to share maritime information to combat illegal activities. But other experts say Biden's move sets a good framework for more security cooperation, though it remains to be seen whether concrete action will follow.
Affected by several factors, the supply of the boron nitride is erratic and thus its prices are expected to go higher in the future.
Hexagonal boron nitride (H-BN) is a two-dimensional layered broadband-gap insulating material with good heat resistance, chemical stability, and dielectric properties. It is widely used in electronic devices.
Hexagonal boron nitride is structurally similar to graphene, consisting of a planar lattice of atoms arranged in interconnected hexagons. The only difference is that in graphene, all atoms are carbon, whereas, in H-BN, each hexagon contains three nitrogen atoms and three boron atoms.
Carbon-carbon bonds are among the strongest, so graphene is theoretically much stronger than H-BN. The strength and elastic modulus of the two materials are similar, and h-BN is slightly lower in comparison: graphene has a strength of about 130GPa and young's modulus of about 1.0TPa; The strength and modulus of H-BN are 100GPa and 0.8 TPA, respectively.
Despite its excellent mechanical properties, graphene has low crack resistance, which means graphene is brittle.
In 1921, British engineer Griffiths published a theoretical study of fracture mechanics, describing the failure of brittle materials and the relationship between the size of cracks in materials and the force required to make them grow. For hundreds of years, scientists and engineers have used this theory to predict and define the toughness of materials.
In 2014, a study by Professor Jun Lou and his team at Rice University showed that graphene's fracture toughness is consistent with Griffith's theory of fracture mechanics: when the stress applied to graphene is greater than the force holding it together, the cracks propagate, And the energy difference is released during crack propagation.
H-bn is also thought to be vulnerable, given its structural similarity to graphene. However, this is not the case.
The scientists found that H-BN is 10 times more ductile than graphene.
A team led by Prof. Jun Lou of Rice University and Prof. Hua Jian Gao of Nanyang Technological University in Singapore has found that the brittle H-BN is 10 times stronger than graphene in cracking resistance. This finding runs counter to Griffith's fracture theory, and such anomalies have never been observed before in two-dimensional materials. The related research results were published in Nature with the title "Intrinsic Toughening and stable crack propagation in Hexagonal Boron nitride".
Mechanism Behind H-BN's Extraordinary Toughness
To find out why, the team applied stress to the H-BN sample, using scanning electron microscopes and transmission electron microscopes to see as much as possible how the cracks occurred. After more than 1,000 hours of experiments and subsequent theoretical analysis, they discovered the mystery.
Although graphene and H-Bn may be structurally similar, boron and nitrogen atoms are not the same, so there is an asymmetric arrangement of hexagonal lattice intrinsic in H-BN, unlike the carbon hexagon in graphene. That is, in graphene, the cracks tend to go straight through the symmetrical hexagonal structure from top to bottom, opening the bond like a zipper. The hexagonal structure of H-BN is slightly asymmetric due to the stress contrast between boron and nitrogen, and this inherent asymmetry of the lattice causes cracks to bifurcate, forming branches.
And if the crack bifurcates, that means it's rotating. The existence of this steering crack requires additional energy to further promote the crack propagation, which makes the crack more difficult to propagate and effectively enhances the toughness of the material. That's why H-Bn shows more elasticity than graphene.
Due to its excellent heat resistance, chemical stability, and dielectric properties, H-BN has become an extremely important material for two-dimensional electronic and other 2-bit devices, not only as a support base but also as an insulating layer between electronic components. Today, h-BN's toughness makes it an ideal choice for flexible electronics and is important for the development of flexible 2D materials for applications such as two-dimensional electronics.
In the future, as well as being used in flexible electronic textiles, h-BN could also be used as flexible electronic skin and implantable electronics that can be connected directly to the brain.
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Trafigura, one of the world's largest metals traders, is to take a stake in a new company to supply car and battery makers in Europe with lithium from a refinery in the UK, the Financial Times reported. As part of the investment, Trafigura will seek raw material for Green Lithium, which plans to build a plant in the north of England capable of producing 50,000 tonnes a year and sell the finished boron nitride, etc. If you are looking for high-quality materials, please feel free to contact us and send an inquiry.