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Hardness is 1.5 times that of diamond
Professor Sun Hong of the Department of Physics of Shanghai Jiaotong University said that humans have been searching for the hardest materials for more than 30 years and invested a lot of money, but they have never broken the hardness of diamonds.
Last year, a French-German cooperation team made a mixture of nanoparticles of cubic boron nitride and wurtzite boron nitride, the hardness of which is close to diamond. However, the material of cubic boron nitride is actually "soft" and its hardness is only about 60% of that of diamond. Therefore, the obsolete wurtzite boron nitride has begun to attract people's attention. This material is a metastable structure and exists only in the form of small particles in nature and in the laboratory.
According to Sun Hong, some people have previously ignored the important effect of the positive pressure on its hardness calculation, so the calculation is not successful. “When subjected to force testing, the material is generally subjected to vertical downward pressure and laterally outward force. The latter force generally destroys the material, but the vertical pressure of some materials will hinder the lateral pressure.†Hiroshi said.
He did the same calculations with the Ph.D. student Pan Yucheng, but considering this effect, the theoretical result was that the material was 18% harder than the hardest known cubic diamond.
For comparison, they also found hexagonal diamonds that are also metastable. Compared to conventional cubic diamonds, hexagonal diamonds can only be found in very small particles. As a result, their hardness is also high or even high. 58% of cubic diamond! Their research was published in the latest issue of the authoritative journal Physical Review Letters.
Superhard materials are widely used
"Modern physics has become a three-legged situation," Sun Hong said. "Before it was divided into two parts of experiment and theory, but the theory must rely on the parameters of the experiment. Now there is computational physics, no experimental parameters are needed, as long as there is the most basic The elements can be calculated by large-scale computers on the basis of quantum mechanics. From the test experience of a large number of known materials, the calculated results are very accurate and convincing."
Although diamond is the hardest natural material, it is unstable in a high temperature environment because of its carbon structure. It is easy to chemically react with oxygen, and it is easy to combine with iron, so it cannot be used in many industries.
The emergence of harder materials means great progress in industry and national defense. In defense, high-temperature resistant superhard materials can be applied to missiles, tanks, earth bombs and even bulletproof vests. In the industry, some deep-sea subsea drilling cannot be replaced, and harder materials will provide a lot of help. If there is a harder material, ordinary people can even use a kitchen knife without grinding. Therefore, harder high temperature resistant superhard materials are widely used in various industrial fields.
Sun Hong said that theorists test that material scientists are looking for materials, which is a cyclic process. Although the material of wurtzite boron nitride is difficult to make a large structure in the experimental environment, at least the theoretical realization provides a research direction for practice, and various materials scientists will try their best to test this in the future. material. Perhaps in the near future, diamonds will really make way from the "hardest material" throne. (written / reporter Jin Yu)
"The world's hardest material" diamond throne is not guaranteed
For a long time, diamonds (diamonds) have always occupied the throne of "the world's hardest natural material". No matter how scientists explore it, they can't find materials that are harder than it. However, since last year, things have changed. Since the French and German scientists made nanomaterials close to diamond hardness last year, the computational physicists at Shanghai Jiaotong University have theoretically calculated the possibility of the two world's hardest materials, which are 18% harder than conventional cubic diamonds. And 58%.