The Big Squeeze In The LabRuth Coxeter
In 1987, C.W. (Paul) Chu of the University of Houston was racing scientists from Moscow to Long Island for a breakthrough in high-temperature superconductivity. On a hunch, he prepared a bit of copper, barium, lanthanum, and oxygen smaller than a BB. Then he worked high-pressure alchemy, squeezing it under pressure 18,000 times as great as that at sea level.
Bingo: When electrodes were plugged in to the blend, it conducted electricity with zero resistance. Chu then guessed he could achieve the same effect at ordinary pressure by substituting yttrium for lanthanum. The substitution worked--and earned Chu worldwide fame for a material that superconducted at a record high temperature: at -180C.
Chu's work highlighted how extraordinarily high pressures can strong-arm elements into yielding their secrets. The high-pressure manufacture of synthetic diamond (by squeezing carbon) is already a near-billion-dollar industry. Today, researchers are using pressures exceeding those at the center of the earth to break and re-form chemical bonds in everything from hydrogen to beach sand. "Even by a conservative estimate, we could triple the range of materials we now know just by squeezing them," says Robert M. Hazen, a research scientist with the Carnegie Institution's Geophysical Laboratory and author of a 1993 book on the topic, The New Alchemists.
If gases can be compressed into stable metallic crystals they might superconduct even at room temperatures. Superhard glass made from silicon dioxide--or quartz--could serve as windshields for rockets. A metallic form of hydrogen could be an incredibly dense form of stored chemical energy. "It would be something like 30 times more efficient than any existing rocket fuel," Hazen says.
The laboratory equipment required to achieve these awesome pressures, a diamond anvil, is no more than 8 inches tall and can be screwed tight by hand. It works by amplifying arm power through gears and concentrating all of it into an extremely small area. That's done by placing a tiny sample between the tips of two cut diamonds. A plate with a hole in it corrals the sample.
Research on such a small scale has big drawbacks. The products are too tiny--about a millionth of an ounce--to be useful for anything except research. Many materials revert to normal once the pressure is off. And high-pressure science can be hazardous. Having witnessed one explosion, David Mao and Russell Hemley of the Carnegie Institution now operate experiments from behind a steel wall.
With real money probably years off, most work on exotic high-pressure materials is going on in universities, not companies. Cornell, Harvard, and the University of California at Berkeley have substantial programs. Three years ago, the National Science Foundation established a Center for High-Pressure Research, pooling efforts at the Carnegie Institution, Princeton, and the State University of New York at Stony Brook.
HARD LUCK. High-pressure research got a jolt last May when 11 Russian and French researchers claimed in the journal Physics Letters that they had created a material harder than diamond from "buckyballs," or carbon-60. But similar claims have arisen before, and some scientists argue that the samples were too small to be reliably tested.
Squeezing materials does more than harden them. Compressing gases such as hydrogen liberates their electrons, turning them into excellent electrical conductors. Helium, ordinarily inert, will bond with nitrogen when sufficiently compressed. Oxygen is ordinarily colorless--but under extreme pressure it forms crystals with facets of red, yellow, and blue. UCLA professor of physical chemistry Malcolm F. Nicol speculates that sulfur crystals could store information, with different colors of light serving to write, erase, and read data.
The quest for a superconducting metallic hydrogen is taking scientists into realms of pressure never experienced on earth--and into heated rivalries as well. Researchers at Harvard University and Carnegie Institution disagree over what happens to hydrogen at 1.5 million atmospheres, or megabars, at which point its molecules line up like satermelons. Carnegie brags it was the first to reach 2.5 megabars. No one has surpassed 3 megabars, where scientists speculate hydrogen becomes fully metallic and superconducting. The big question: Will metallic hydrogen remain metallic once the pressure is off?
MICROPOPS. Commercialization is just one goal. High-pressure researchers also seek to understand the composition of stars and planets and the sources of earthquakes. UCLA's Nicol has even recreated conditions of the early earth to form chains of hydrogen cyanide, which he believes are precursors to DNA. One favorite for research is ikaite, a watery calcium compound. Its behavior under high temperature and pressure sheds light on how veins of gold, silver, and other ores are formed. Raymond Jeanloz, a physicist at UC Berkeley, and graduate student Charles Meade proposed a new seismic theory after pressurizing serpentine, a greenish, waxy mineral. A microphone attached to a diamond anvil picked up a popping sound--perhaps a miniature version of a quake that occurs when water is forced out of serpentine deep underground.
Doubts about the commercial value of exotic high-pressure materials have kept away mainstream producers of synthetic diamonds, such as General Electric, Sumitomo, and De Beers. "We're a materials supplier. Just creating high-pressure phases doesn't make you any money," says William F. Banholzer, manager of engineering for GE Superabrasives in Worthington, Ohio. But in labs like Paul Chu's, the big squeeze is paying off. Chu recently found a superconductor that he hopes could be produced in industrial quantities by depositing the materials in vapor form. That's the kind of advance that keeps the pressure on.
It's not just making diamonds from graphite: All kinds
of ordinary materials take on startling characteristics when subjected to extremely high pressure.
MATERIAL POTENTIAL USES
HYDROGEN, OXYGEN Fuel cells, superconductors
CARBON-60, OR BUCKYBALLS Coatings for computer disks, abrasives
SILICON DIOXIDE Superhard glass, lightweight car components
IKAITE Indicator of how mineral deposits form
HELIUM NITRIDE Aid to research on inert gases