Scientists create nonexpanding metal using high pressure

June 16th, 2009 - 2:16 pm ICT by ANI  

Washington, June 16 (ANI): Scientists at the California Institute of Technology (Caltech), using high pressure, have created a material that does not expand when heated, and acts like a metal with an entirely different chemical composition.

For creating this material, the scientists had to squeeze a typical metal alloy at pressures hundreds of thousands of times greater than normal atmospheric pressure.

The discovery offers insight into the exotic behavior of materials existing at high pressures, which represent some 90 percent of the matter in our solar system.

Zero-expanding metal alloys were discovered in 1896 by Swiss physicist Charles Edouard Guillaume, who worked at the International Bureau of Weights and Measures in France.

While attempting to develop an inexpensive international standard for the meter, the metric unit of length, Guillaume hit upon an inexpensive iron-nickel alloy that expands very little when heated.

He dubbed the material an “Invar” alloy-because the metals are “invariant” when heated, such that the length of a piece of Invar metal does not change as its temperature is increased, as do normal metals.

Because of their unresponsiveness to temperature change, Invar alloys have been used in devices ranging from watches, toasters, light bulbs, and engine parts to computer and television screens, satellites, lasers, and scientific instruments.

Caltech graduate student Michael Winterrose, and his colleagues examined the effect of pressure on the alloy of palladium (Pd) and iron (Fe) called Pd3Fe, where three of every four atoms are palladium, and one is an iron atom.

“The Fe and Pd atoms (in the alloy) have very different sizes, and we expected to see some interesting effects from this size difference when we put Pd3Fe under pressure and measured its volume,” Winterrose explained.

To test this, the scientists squeezed a small sample of the material between two diamond anvils, generating pressures inside the sample that were 326,000 times greater than standard atmospheric pressure.

“Our initial results from these studies showed that the alloy stiffened under pressure, but far more than we expected,” Winterrose said.

To figure out the cause, the scientists simulated the quantum mechanical behavior of the electrons in the alloy under pressure.

“The simulations showed that under pressure, the electrons found the special energy levels between strong and weak magnetism that are associated with normal Invar behavior. Up to this point we had been quite unaware of the possibility for Invar behavior in our material,” Winterrose said.

According to Winterrose, the scientists had performed a kind of high-pressure “alchemy” on the alloy, where pressure makes the electrons act as if they are around atoms of a different chemical element. (ANI)

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