Everybody's Best Friend, Maybe
Molecule of the Year: that was the cover headline on the December 21 issue of the journal Science. Suspecting the magazine's editors were praising some new and complex chemical, I set that copy aside.
But everything gets scanned before it's tossed, so I finally learned which molecule was honored. It's not new and it's not chemically complex. It contains just one element--carbon. The designated molecule of the year 1990 is diamond.
What Science magazine celebrated amounts to the domestication of diamond. The year just past, according to chief editor Daniel Koshland, marked technical advances "on a pathway of major importance:" producing inexpensive synthetic diamond, in both crystalline and film forms.
That may sound uninteresting to anyone not in the market for an engagement ring, but artificially produced diamond may change all our lives. This often-beautiful form of pure carbon has many extraordinary (and potentially very useful) properties.
Diamond is the hardest substance known. It is transparent to visible light, x-rays, ultraviolet light, and most of the infrared portion of the spectrum. It conducts heat better than any other material yet found, but has extremely high electrical resistance. It is inert to chemical corrosion.
Until fairly recently, these practical attributes have been little used. Natural diamonds are too scarce. They form deep in the earth, in the high temperatures and pressures of the mantle. Only volcanoes that erupt material from such depths bring diamonds up into crustal rock where people can find them. South Africa's deep diamond mines follow old volcanic rock conduits; elsewhere---including Alaska, apparently---diamonds are found in placer deposits, eroded and transported away from their original volcanic source by moving water.
The first U.S. patent for synthesizing diamond was awarded in 1958. The process required burning methane at very high temperatures under pressures of 55,000 bars (Earth's atmosphere exerts approximately 1 bar). As the methane burned, it left behind deposits of nearly pure carbon --- but some of it was in the form of soft platelets of graphite rather than hard crystals of diamond.
Soviet researchers fixed that. In 1977, they found that introducing atomic hydrogen to the pressure chamber prevented graphite formation. By 1981, they were producing multiple-crystal diamond films on metal substrates.
Shortly thereafter, Japanese and other researchers began to develop low-pressure methods for depositing diamond films. In these chemical vapor deposition (CVD) methods, hydrogen gas and a simply hydrocarbon such as methane are heated together to temperatures of 2200oC (3992oF). The carbon atomizes, ionizes, then rearranges and condenses out as a film of diamond onto the substrate in the chamber. CVD methods have steadily improved over the decade, and now provide films smoother, larger and cheaper (presently about $100 a carat) than any earlier technique produced. For human purposes, the diamond materials in some ways even better than the natural product.
Thanks to such technical progress, the Science editors believe, we are close to a diamond revolution. Diamond in electronic circuits could do away with cumbersome cooling systems---diamond transports heat so efficiently they won't be needed. Diamond diodes have been fabricated at the laboratory bench; if these building blocks for transistors (and hence integrated circuits) can be produced in a factory, heat-hardy diamond devices could replace silicon chips.
Diamond film-covered metals could be fashioned into near frictionless bearings needing little or no lubrication---equally useful in deep space or in artificial limbs. Diamond films on glass could yield scratchproof, nonreflecting lenses. And cast-diamond products, nozzles and tubes, have also been produced.
The Molecule of the Year article even noted a product bound to sell well in Alaska as soon as it's available: polycrystalline diamond film-coated steel blades for saws and knives. They'd never need sharpening or replacing---but they probably won't look good in an engagement ring.
