Ceramic yields under pressure
Technology Research News
Ceramic is usually unyielding. It responds
to pressure by resisting fully, or, when the pressure is too great, by
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,
February 26/March 5, 2003
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