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Persistence pays off with zeolite gem.

Once too small to see with the naked eye, those inorganic crystals called zeolites will soon come in extra-large sizes, thanks to the persistence of a team of chemists. Scientists have grown near-perfect zeolite crystals that measure several millimeters across. And they expect to make bigger, better specimens soon, Walter G. Klemperer of the University of Illinois in Urbina-Champaign announced this week at the spring meeting of the American Chemical Society in San Francisco.

Usually, "[zeolites] are more on the other of tens of microns," says Klemperer. "But these are things that you can mount on a ring."

Scientists use these compounds -- whose internal structure resembles a Swiss cheese -- as molecular sieves, catalysts for refining petroleum and even water softeners. Zeolites appeal to chemists because of their large surface areas and their internal cavities, or channels, which are big enough to admit small molecules but small enough to contain the product formed when those moleducles react inside the crystals. Scientists have increased the size of these channels (SN:8/3/91, p.77) but have shield from making large crystals because of the technical difficulty of the task.

Klemperer and his group at Illinois worked three years and finally got decent macroscopic crystals on the 327th try. Larger crystals provide better views of the internal organization of the zeolites, says Klemperer. Already the Illinois group and colleagues at the University of Nebraska in Lincoln have observed how temperature changes affect this organization. Next they plan to grow larger, more perfect crystals and to make ones with channels that will allow guests atoms to travel throughout the crystals.

Just as the development 40 years ago of methods for making macroscopic quartz crystals led to many new applications for that material, this work "opens up enormous potential for zeolites," Klemperer says. Bigger zeolites could prove important in a wide range of optical and electronic applications.
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Author:Pennisi, Elizabeth
Publication:Science News
Date:Apr 11, 1992
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