Carbon gourds hold gas, not water.

If sheets of graphite can wrap themselves into balls, tubes, and onions, as researchers have found, why not into gourds?

Zhong Lin Wang and his colleagues at the Georgia Institute of Technology in Atlanta have discovered that carbon can indeed take on such a structure, which they are calling a calabash. Consisting of two carbon spheres joined at the hip, it looks much like the dumbbell-shaped gourds that people use to carry water in many parts of the world, Wang says.

The newly discovered carbon structures are about 0.5 micrometer across, 1,000 times larger than buckyballs. Through an electron microscope, the researchers can see that some of the calabashes are hollow, while others have solid cores. Wang described the calabashes last week at a meeting in Boston of the Materials Research Society.

To make the calabashes, the scientists allow methane gas to flow over a powdered catalyst placed at one end of a quartz tube. They heat the tube gradually to 1,000 [degrees] C. The methane decomposes, and carbon spheres and calabashes form on the walls of the tube.

The researchers detected the calabashes after changing the catalyst they ordinarily use to make pure carbon spheres. With the new catalyst, about 90 percent of the structures created are spheres, 5 percent are calabashes, and the remainder form a variety of shapes. Wang and his team are currently trying to improve the yield. "We need to make larger quantities to do [additional] spectroscopy" to learn more about their chemical properties, he explains.

The calabashes appear to be much like carbon onions, structures with concentric graphite layers, being studied for use in hard coatings (SN: 8/31/96, p.139), says Jagdish Narayan of North Carolina State University in Raleigh. Calabashes, however, would probably be tapped for other applications.

Like their namesake, the carbon calabashes could be used to carry things. Wang's group has found oxygen gas trapped inside some of the hollow structures. If the calabashes could trap other gases--hydrogen, for example--they might serve as portable storage for gaseous fuel.