Technology: Say It with Sewage Gas

The medieval alchemists who tried to turn base metals into gold had the right idea, but they may have set their sights too low. Using modern techniques, scientists at the U.S. Naval Research Laboratory have accomplished an even more amazing transformation: they have turned sewage gas into diamonds.

Diamonds, the crystalline form of carbon, are usually formed when organic solids are subjected to intense heat and pressures. But under the right conditions, the glittering crystals can also be manufactured from a carbon- rich gas — something the Navy’s lab has in abundant supply. Its facilities abut Washington’s giant Blue Plains Waste Water Treatment Plant, which each day generates 650,000 cu. ft. of methane (CH4). Tapping that supply, chemist James Butler passed a sample of the gas over a filament of tungsten glowing at 4,000 degrees F. To his delight, a sparkling film of synthetic diamonds began to appear. The searing heat had knocked carbon atoms loose from the methane, allowing them to settle, layer by layer, into crystal patterns.

Butler’s rocks will not turn any heads at Cartier; the largest is a few thousandths of an inch thick. But the sturdy crystals could be used to make wear-resistant machine tools, for example, or scratch-proof lenses. Diamonds would even make first-rate computer chips if they were not so expensive to produce. Butler’s technique could help solve that problem. “The gas is free,” he points out, “and the supply is virtually unlimited.”