Earth has much less xenon than any other rocky planet, and no one knows why: it isn't locked up in chemical compounds, and it's too heavy to have escaped into space. When Steven Louie heard it was missing, he set out to track it down.
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 Supercomputer simulation reveals that even under extreme pressure, iron and xenon cannot form a compound.
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What if xenon could form a compound with molten iron in the Earth's core? This was a longtime conjecture in the field. Louie's group used computers to simulate the behavior of xenon under extreme pressure and heat, while his geophysicist colleague Raymond Jeanloz applied real pressure and heat with a diamond-anvil cell and a laser beam.
Diamond-anvil cells achieve pressures like those in the Earth's liquid core, but computers simulate pressures even greater. The diamond-anvil experiments agreed with computer calculations showing that chemical bonds between xenon and iron are impossible, even at pressures greater than the center of the Earth.
Where is the missing xenon? Not in the iron core. Through a collaboration of calculation and experiment, a false trail has been eliminated. The search goes on.
| Nanopasta carbonara, boronara, nitronara . . . When it comes to making nanotubes, carbon isn't the only game in town. Nanotubes made of boron nitride act as semiconductors no matter which way the "chicken wire" is wrapped, Louie and Cohen predicted. They've also designed tubes of boron, carbon, and nitrogen, along which electrons would spiral from carbon to carbon, and of boron carbide, a semiconductor that would form a metal when the tubes are packed together in bundles. Because nanotubes are millions of times longer than they are wide, and because carbon nanotubes in the lengthwise direction are the strongest material known, experimenters are developing many other possible applications, including rugged flat screens for TVs and computers, atomic-scale "hypodermic needles," and solid storage tanks for hydrogen. Graphite-like bonds form other nanostructures too, including new kinds of hollow "buckyballs" and nano-"peapods" with buckyballs nesting in tubes. Nano-"peashooters" that propel buckyballs may not be far behind.
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