OREGON STATE UNIVERSITY

NEW COMPOUND DISCOVERED WITH ELECTRONICS, OTHER POTENTIAL

04/04/1996

CORVALLIS, Ore. - Oregon State University researchers will announce Friday in the journal Science that they have discovered a new compound which contracts, rather than expands, when heated over a wide range of temperatures.

A multitude of electronic, optical and other applications may be possible for this material, which has received patent approval.

About 25 companies around the world have expressed an interest in evaluating this material for various applications.

The compound, called zirconium tungstate, has highly unusual physical characteristics. It's also a major improvement over a material which showed similar properties but in a much narrower temperature range, scientists say.

"This compound is unique," said Arthur Sleight, the Milton Harris Professor of Material Science at OSU. "No other known compound has ever shown qualities like this."

The future of the compound, researchers say, is probably to be used in a "composite" form with other materials, creating various products that neither expand nor contract when they are heated or cooled.

Such an unusual behavior might eliminate the expansion or contraction of electronic circuit boards that can sometimes cause their failure. It could improve the performance of ceramics in electrical insulators, or the optical performance of telescopes and other delicate instruments.

For instance, Sleight said, a polymer-based composite might be developed in which an electronic circuit board had thermal expansion characteristics identical to those of the silicon computer chips which it held.

An option to market and manufacture the material has been granted to Teledyne Wah Chang, an Albany, Ore., manufacturer of specialty metals.

That company has provided private industrial support to this OSU research program with grants of more than $100,000 over the past five years. They have learned how to produce this material, Sleight said, and are making evaluation quantities of it available to interested parties.

"We're very interested in the prospects for this material," said John Haygarth, a scientist with Teledyne Wah Chang. "This compound has the very uncommon property of shrinking uniformly when it is heated.

"It could be a solution that's now looking for some problems to solve," Haygarth said.

About two years ago, OSU scientists identified a related oxide of zirconium, vanadium and phosphorus, which showed this characteristic of "negative thermal expansion" somewhat above room temperature.

Further studies, however, have revealed much about the fundamental chemistry and physics that create this phenomenon. This led to the discovery of the new material that has uniform, negative thermal expansion from near absolute zero to 1,500 degrees Fahrenheit.

Such behavior has never before been observed. Nearly all materials expand when they are heated, as their chemical bonds lengthen and atoms move further apart.

Some known materials, such as those commonly used in a type of kitchen bakeware, are made of small particles that, when heated, expand in one direction while contracting in another. This can lead to very low overall thermal expansion and resistance to breaking from thermal shock.

The new compound of zirconium, tungsten and oxygen contracts uniformly along all dimensions when heated, even at extreme ranges of temperature.

The key to this behavior is vibration of the oxygen atoms which bind the atoms of zirconium and tungsten together. As temperatures increase, the oxygen atoms vibrate more strongly and pull the other atoms closer.

"We never expected to find materials with this quality over such a broad temperature range," Sleight said. "For many applications, we only needed to obtain this behavior from a temperature range of about minus 60 to plus 300 degrees Fahrenheit. We now have that covered and quite a bit more."

Continuing research may ultimately allow the creation of still more and perhaps even very low cost materials with this characteristic, Sleight said. The findings so far, which were outlined today in the Science publication, have led the OSU research team in several promising directions, he said.

Collaborators on these studies at OSU, which were conducted through the Center for Advanced Materials Research, were research associates John Evans and T.A. Mary. It was supported by the Oregon Metals Initiative, a joint initiative of academic institutions, other agencies and private industry.

The findings were also made possible by a sophisticated structure-solving instrument at a research reactor at Brookhaven National Laboratory.