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Shuttle surprise: zeolites form odd rods.

When chemical engineer Robin Stewart peeked into a test chamber she had sent into space last April, the last thing she expected was some rod-shaped crystals. She and her co-workers had set up an experiment to grow an inorganic compound called a zeolite during the six-day flight of the shuttle Atlantis. Usually, zeolites form cubic or octahedral crystals, so the rods came as quite as surprise, she says.

Zeolites occur naturally as minerals in metamorphic rock. These aluminum-silicate compounds are full of holes and can sop up and ooze water. Within the cubic formation, zeolite atoms arrange themselves into tetrahedral rings that link up to form tiny channels. Thus, chemists can use them as molecular sieves, catalysts and even water softeners. Zeolites play a key role in refining gasoline, and chemical companies use them to separate molecules of varying sizes and shapes and to absorb gases and vapor mixtures. Scientists continue to explore new ways to make these multipurpose crystals, Stewart says.

Outer space offers one new approach. As a material crystallizes on Earth, gravity can cause some crystals to settle out, leaving flaws in the material. So chemists seeking perfect samples for analysis find the space shuttle an attractive environment for their experiments. Until April, chemists tended to use the shuttle primarily for crystallizing proteins. In most cases, the materials assume the same shape in space as they do on the ground, Stewart says. However, one team did get unusual lead iodide crystals from space experiments conducted two years ago (SN: 9/23/89, p.206).

Stewart and several colleagues at the National Institute of Standards and Technology's Biophysical Measurements Group in Boulder, Colo., undertook their zeolite project in collaboration with Instrumentation Technology Associates, Inc., of Exton, Pa. The researchers set up a reaction vessel that allows the chemicals that form zeolites to ooze into a gel, where they combine to form crystals. Stewart sent up several experiments on the shuttle and ran identical tests in her lab as controls. In space, she says, "the only thing we took away was gravity."

The microscopic rods returned by Atlantis proved that zeolites can grow in the span of a short shuttle flight, Stewart says. However, since the crystals were too small for more detailed study, she does not know why they took on an elongated shape.

"It actually raises more questions than it answers," she says. "But the first time through, you never do know what you will get."

Stewart, now with ADA Technologies in Englewood, Colo., says she hopes to try again and get larger zeolite crystals from space.
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Title Annotation:inorganic compound forms rod-shaped crystals after experiment aboard space shuttle Atlantis
Author:Pennisi, Elizabeth
Publication:Science News
Date:Jul 13, 1991
Words:430
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