Question

When graphite is subjected to a beam of x-rays, _____________ occurs.​

Answer 1

Answer:

Atoms in graphite under high pressure appear to form a ... and found that this combination closely matched the x-ray ...

Answer 2

Explanation:

Squares of carbon. In bct-carbon, 4-atom rings are joined together in a three-dimensional network (above; “short” bonds come out of the plane of the screen). A perpendicular view (top) shows the vertical arrangement of the squares (shown edge-on as h... Show more

Pure carbon has a wide variety of atomic structures, such as diamond and graphite, but the structure created by a 2003 graphite compression experiment has been controversial. Now two teams of theorists have followed different lines of evidence to suggest that the structure involves a 3D network of four-atom rings called bct-carbon. In the 26 March Physical Review Letters, one team reported simulations that agree with the 2003 data, and in the October Physical Review B, the other team shows that the energy barrier to create bct-carbon is low enough that it could have appeared in the 2003 experiment. Researchers say the results point to the existence of a new and unexpectedly simple form of carbon.

Since the early 1960s researchers have known that graphite undergoes a reversible transformation when subjected to high pressure at room temperature, known as cold compression. But the chemical and structural changes to the carbon atoms remained largely mysterious. Then in 2003 a team reported cold compression of graphite in a diamond anvil press and simultaneous exposure of the sample to x rays to study its chemical bonding [1]. At pressures greater than 17 gigapascals (170,000 atmospheres), the sample entered a phase in which the carbon atoms formed three or four chemical bonds with their neighbors. The structure was distinct from diamond, which appears at higher temperatures and pressures. “It looked closely related to graphite,” says Wendy Mao of Stanford University, who was part of the 2003 study, but it could scratch diamond.

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