Ice resists melting in warm conditions - methane clathrate may protect ice from melting - Materials Science - Brief Article

Science News, Oct 19, 1996

What seemed to be a straightforward material synthesis took an unexpected turn for scientists at the U.S. Geological Survey (USGS) in Menlo Park, Calif. They were testing a new way of making samples of methane clathrate so they could measure its mechanical properties. The researchers combined tiny grains of ice with gaseous methane at a low temperature, then allowed the mixture to warm slowly and react to form the clathrate, a solid in which water molecules form cages that trap a gas.

As the mixture crept above 0#161#C, however, the ice didn't melt. Even when the reaction reached completion, at temperatures near 16#161#C, grains of pure ice lingered in the vessel. "The full reaction to form the clathrate took about 8 hours, and we never saw wholesale melting of the seed ice," says Laura A. Stern, a USGS geophysicist. Stern and her colleagues report their findings in the Sept. 27 Science.

At first, the researchers thought they had measured incorrectly or that some- thing was wrong with their apparatus, Stern says. However, a control experi- ment using neon gas, which does not form a clathrate, ruled out those pos- sibilities. "All the ice melted in about 30 minutes," she notes.

Jeffrey Kargel, a geologist with USGS in Flagstaff, Ariz., struggled to accept the results but came to believe that the researchers "are basically on the right track." A similar effect has been seen in gold-plated silver grains, he says, where the gold forms a layer that protects the silver from melting. The clathrate probably does the same for the ice.

Although the effect lasted for many hours, this phenomenon is no ice-nine-the fictitious substance that turns the whole Earth solid in Kurt Vonnegut Jr.'s novel Cat's Cradle. The ice, Stern says, won't survive indefinitely at high temperatures. Left out on a tabletop, methane clathrate dissociates into its constituents, leaving nothing but a puddle of water. Still, Kargel says, "if [the results] can be verified, they will be full of insights into the dynamics of melt nucleation."