Ceramic yields under pressure

By Kimberly Patch, Technology Research News

Ceramic is usually unyielding. It responds to pressure by resisting fully, or, when the pressure is too great, by breaking.

Researchers from Drexel University and Oak Ridge National Laboratory have stumbled on a ceramic-like material that compresses and springs back.

The compression is fairly small under even very high pressure, meaning the material absorbs a lot of mechanical energy. If an elephant stepped on a small cylinder of the material, for example, the compression would not be visible, according to Michel Barsoum, a professor of materials engineering at Drexel University. "The changes are less than one percent."

The ability to dissipate mechanical energy makes it a good dampener for vibrations including noise. "The amount of energy it absorbs... is quite large," said Barsoum. The material could be used in machinery and transportation equipment, and in electronics, including microelectromechanical systems (MEMS) to, for instance, cut down on wobbling in disk drives, according to Barsoum.

The material is a mix of titanium, silicon and carbon, and is one of a class of at least 50 such materials that the researchers discovered accidentally, said Barsoum. "We were trying to make some very hard materials and stumbled on the... MAX phases." MAX refers to the three elements that make up this group of molecules -- an early transition metal, an A-group, or main group element, and carbon or nitrogen.

The material can handle stresses of up to 1 giga pascal, or 145,000 pounds per square inch, and can dissipate up to 25 percent of that mechanical energy by compressing. This high rate of dissipation is more than most woods and is comparable to materials like polypropylene and nylon. When the load is removed it springs back fully, Barsoum said.

At the same time, the material is as dense as the metal titanium, and a better conductor of electricity and heat. It is stiff, lightweight and machinable, making it relatively easy to work with, said Barsoum. It is three times as stiff as titanium but can be cut with a manual hacksaw. The material also has a low coefficient of friction, which makes it feels like soap, and withstands temperatures as high as 1,650 degrees Celsius.

The substance belongs to "a new class of materials with unique and unusual properties -- they are neither ceramics nor metals but seem to combine some of the best properties of both," said Barsoum.

The material's unusual characteristics have to do with the way the molecules pile up, or kink under pressure, then stretch out again when the pressure is removed. These actions take place along a plane within individual grains of the material. Course-grained samples of the material dissipate the most energy, according to Barsoum.

The material could be used in products within two years, said Barsoum, who has started a company to commercialize the material.

The company has manufactured several prototypes, said Barsoum. The prototypes are "past the proof-of-concept stage," he said. Some are in the final valuation stages and that should be followed by mass production."

Barsoum's research colleagues were Tiejun Zhen, Surya Kalidindi and Anand Murugaiah from Drexel University and Miladin Radovic from Oak Ridge National Laboratory. The work appeared in the February, 2003 issue of Nature Materials. The research was funded by the National Science Foundation (NSF), the Army Research Office (ARO) and Kanthal Corporation of Sweden.

Timeline:   1-2 years
Funding:   Corporate, Government
TRN Categories:  Materials Science and Engineering
Story Type:   News
Related Elements:  Technical paper, "Fully Reversible, Dislocation-Based Compressive Deformation of Ti3SiC2 to 1 GPa," Nature Materials, February, 2003.


February 26/March 5, 2003

Page One

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