When the graphite-bearing meteorite hits the earth, the high temperature and high pressure generated by the impact can transform the graphite into a rare and extremely hard diamond. The scientific community has long been controversial about how this transformation occurs at the atomic level. Now, scientists have solved some of these puzzles by simulating and real-time observation of the moment of impact.
In the first such impact laboratory built at the Argonne National Laboratory, Washington State University physicist Yogendra Gupta and colleagues 5.1. At a speed of kilometers per second, a lithium fluoride-filled bullet is directed at a graphite disk, in this way to simulate a meteorite impact, and to use ultra-bright X-rays to "shoot" the process at a frequency of 150 billion frames per second.
“When it comes to the formation of diamonds by meteorites, people always ask, at what stage of the transition, whether it is in the compression phase or in the two stages of stress release after compression and impact,†Gupta said. "Our experiments make it very clear that this shift took place during the compression phase." Specifically, at 500,000 times atmospheric pressure, graphite forms such a rare hexagonal diamond (named after crystal structure) in billions of seconds. New findings suggest that the impact strength required to form diamonds may not be as great as scientists thought.
Gupta said that earlier research showed that hexagonal diamonds need to be formed at nearly 2 million times atmospheric pressure, but this figure is "very controversial." Other studies have shown that the structure of graphite begins to change at lower pressures, but X-ray tests in these experiments have shown that diamonds formed at lower pressures are mixtures of many different structures, so it has been “No one knows exactly when the transition process begins,†Gupta explained. Most of the earlier studies studied atomic transformation under conditions of increasing pressure. In contrast, Gupta and colleagues have shown that a sudden impact can directly form hexagonal diamond, and the internal structure of the formed diamond is completely determined by the direction of impact. The study was published in the October 2017 issue of Science Advances.
Lorin Benedict, a physicist at Lawrence Livermore National Laboratory, said that "the most exciting part of the research is that researchers Determines the exact location of the atom at which the impact occurs when one crystal form is converted to another."
The diamond obtained in this way retains its structure after the pressure drops, but Gupta wants to know if the diamond will remain stable after the pressure has completely disappeared. Such an experiment may result in a completely new approach to the preparation of industrial diamonds.
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