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March 21, 2000

Scientists Gain Molecular Understanding
of How Clays Behave When Wet

UPTON, NY-Knowing how clays absorb water at varying temperatures and humidities could help shore up undersea oil wells and improve the understanding of soil characteristics at construction sites. Now, using X-ray scattering at the National Synchrotron Light Source (NSLS), located at the U.S. Department of Energy's Brookhaven National Laboratory, scientists have developed a way to "fingerprint" and monitor the movement of water into and out of clays.

The microscopic structure of clay consists of layers of minerals with spaces in between. When water enters the clay, it forces the layers apart, explains Brookhaven physicist Elaine DiMasi, who is presenting the research at a March 21 session of the American Physical Society meeting in Minneapolis.

At the NSLS, DiMasi and her collaborators from the Norwegian University of Science and Technology (NTNU) analyze the scattering patterns produced by high-intensity X-rays beamed at the clay while varying the moisture level. When looking at clays under hot, dry conditions, the scientists identify characteristic peaks in the directions of scattered X-rays. These peaks correspond to the distance between the crystal layers. As water enters the clay, the peaks change dyanmically in a way that corresponds with the increasing space between the layers.

"The peaks are like a fingerprint that's associated with the different hydration conditions," DiMasi says. This method can help scientists determine at exactly what temperature or humidity level the water goes in or out, and monitor the transition from wet to dry or vice versa over time.

"There are forces between all these atoms that limit the way the water molecules can get in and out," DiMasi says. "If we want to know about that, these kind of time-dependent measurements can be very useful."

Such precise measurements may help scientists make more accurate generalizations and predictions about the behavior of clays.

One immediate application is in the drilling of oil wells through undersea clay beds. DiMasi has been collaborating with physicist Jon Otto Fossum at NTNU in Trondheim, Norway. Fossum's research into physical phenomena in synthetic clays is of interest to oil-related industries in Norway and in the U.S. "They really need to know about how temperature affects the clay, and how to deal with wet clay, and how to trick that clay into behaving differently when necessary to shore up the wells they are drilling," DiMasi says. The synchrotron X-ray studies may also help in "calibrating" signals picked up by modern logging tools, such as nuclear magnetic resonance (NMR), when used in clay-rich oil wells.

Understanding clay's water-absorbing behavior may also help geologists assess the suitability of certain types of soil for construction and predict more accurately how much water is carried by the movement of the Earth's tectonic plates.

"When we do X-ray scattering studies, we are looking at crystal structures - where the atoms are, how they are lined up to form a solid and what arrangements they have," DiMasi says. "But the details of the microscopic structure affect the properties that a big bulk of the material has" - even bulks as large as Earth's tectonic plates.

This paper will be presented at session I33 on March 21, 2000, at 2:30 p.m. in room 213B of the Minneapolis Convention Center.

The U.S. Department of Energy's Brookhaven National Laboratory creates and operates major facilities available to university, industrial and government personnel for basic and applied research in the physical, biomedical and environmental sciences and in selected energy technologies. The Laboratory is operated by Brookhaven Science Associates, a not-for-profit research management company, under contract with the U.S. Department of Energy.

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Note to local editors: Elaine DiMasi lives in Miller Place, N.Y.

Last updated 5/28/99 by Public Affairs