OREGON STATE UNIVERSITY

New compound reveals more secrets, potential

01/02/1997

CORVALLIS, Ore. - Scientists today announced new findings on a compound that contracts instead of expands when heated, and already has been hailed as one of the top scientific advancements of 1996.

These latest findings, outlined in the professional journal Science, shed further light on the structure of "zirconium tungstate," its behavior under high pressures, and its potential for practical uses, scientists say.

The discovery of zirconium tungstate by Oregon State University researchers has been patented. Cited by Discover Magazine as one of the top 100 scientific advances of 1996, it is gaining more and more interest from private industry as its properties and potential are more fully understood.

"Zirconium tungstate is unique in a very real way, and some manufacturers we've spoken to are quite astounded," said Arthur Sleight, the Milton Harris Professor of Materials Science at OSU.

More than 40 private companies at this point have requested material samples, and applications are now being considered in electronics, optics, fuel cells, oxygen sensors, thermostats, and even new dental filling products.

The latest advance reported in Science, Sleight said, outlined how zirconium tungstate behaves under pressures of 1,000 "atmospheres" or more. It somewhat surprised researchers when its crystal structure collapsed and formed molecular "cross braces" under moderate pressures, while losing much of the "negative thermal expansion" characteristic that makes it so unique.

But when heated moderately, the material then regained this odd characteristic of shrinking when heated. What this suggests, Sleight said, is possible use of the material in some type of composite that could serve as a "shock absorber."

"A material with this type of behavior might be able to absorb an explosive force and then somewhat regain it's shape," Sleight said. "And we're also learning more about the unusually high oxygen mobility of this material, which suggests possible uses in fuel cells or oxygen sensors."

Another of the more intriguing uses of the material, and one which has perhaps excited the most interest among industrial users, is in dental care.

"We've seen a surprising number of requests for the material from dental product companies," Sleight said. "It appears that one of the chief causes of failure in tooth fillings is thermal expansion and contraction, since teeth are routinely exposed to temperatures ranging from hot coffee to ice cream."

A new composite material made with zirconium tungstate - which is non-toxic and could probably be made in colors similar to those of teeth - might produce new types of fillings with thermal expansion characteristics that matched those of people's teeth, scientists say.

All of the future applications of this material are still on the experimental drawing board, but Sleight said he is "more optimistic than ever about the potential for real world uses."

Further advances have also been made in producing the compound at temperatures about half of those used previously, which would simplify some manufacturing and engineering processes.

The discovery of zirconium tungstate was an outgrowth of work in OSU's Center for Advanced Materials Research. It was supported by the Oregon Metals Initiative, an Oregon collaboration of academic institutions, other agencies and private industry.

The studies have also been heavily funded by Teledyne Wah Chang, an Albany, Ore., manufacturer of specialty metals which has an option to market and manufacture this material, and is providing test samples to industry.

Researchers say that the future of zirconium tungstate is to be used in a composite form with other materials, creating various products that neither expand nor contract when they are heated or cooled.

Or, it could be used to create products that expand when heated at a certain controlled rate - such as the rate of expansion of silicon. A composite with this characteristic might form an ideal base for an electronic circuit board which had thermal expansion characteristics identical to those of the silicon computer chips which it held.

Zirconium tungstate has this unusual characteristic of negative thermal expansion from near absolute zero to about 1,500 degrees Fahrenheit. Such behavior in a material had never before been observed. It's now known to be caused by oxygen atoms in the material "vibrating" when heated and pulling zirconium and tungsten atoms closer together.

Officials at Teledyne Wah Chang have said the new material is "a solution that's now looking for some problems to solve."