Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Caltech scientists use high-pressure 'alchemy' to create nonexpanding metals

17.06.2009
By squeezing a typical metal alloy at pressures hundreds of thousands of times greater than normal atmospheric pressure, scientists at the California Institute of Technology (Caltech) have created a material that does not expand when heated, as does nearly every normal metal, and acts like a metal with an entirely different chemical composition.

The discovery, described in a paper in Physical Review Letters (PRL), 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 Édouard 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. Since Guillaume's discovery—which, in 1920, earned him the Nobel Prize in Physics (besting Albert Einstein, who was awarded the prize in 1921)—other nonexpanding alloys have been identified.

It has long been known that Invar behavior is caused by unusual changes in the magnetic properties of the alloys that somehow cancel out the thermal expansion of the material. (Normally, heat increases the vibrations of the atoms that make up a material, and the atoms prefer to move apart a little, causing expansion.)

"Recent computer simulations indicate that electrons in Invar alloys take on a special energy configuration," says Caltech graduate student Michael Winterrose, the first author of the PRL paper. "This energy state is at the borderline between two types of magnetic behavior, and is very sensitive to the precise ratio of elements that make up the alloy. If you move away from the Invar chemical composition by only a couple of percent, the energy configuration will disappear," he says.

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. "In our day-to-day lives, we are surrounded by items that make essential use of Invar alloys," Winterrose says.

The Caltech scientists did not set out to study Invar behavior—and, in fact, were hoping to avoid it. "We intentionally picked chemical compositions that do not show Invar behavior because I thought it would confuse our interpretations," says Brent Fultz, a professor of materials science and applied physics at Caltech, and a coauthor of the PRL paper.

Instead, Winterrose, Fultz, and their colleagues were examining 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. (In the similarly named but chemically distinct PdFe3—which is a traditional Invar alloy—three of every four atoms are iron, and one is palladium).

"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 explains. 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," he says. 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 says.

Subsequent experiments at the Advanced Photon Source at Argonne National Laboratory in Chicago and the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory in New York confirmed that the intense pressure had indeed suppressed thermal expansion in Pd3Fe, much like tuning the chemical composition.

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, Winterrose says.

The research helps unify our understanding of Invar behavior, which is one of the oldest and most-studied unresolved problems in materials research. In addition, using pressure to force electrons into new states can point to directions in materials chemistry where new properties can be found, at least for magnetism.

"Today, materials physics has some excellent computational tools for predicting the structure and properties of materials, although there are suspicions about how well they work for magnetic materials," says Fultz. "It is satisfying that these computational tools worked so well for showing how pressure changed the material into an Invar alloy. Invar behavior is pretty subtle, requiring a very special condition for the electrons in the metal that is usually tuned by precise control of chemical composition. Pressure can make the electrons behave as if they are in a material of different chemical composition, so I really like Mike's use of the word 'alchemy'."

The paper, "Pressure-Induced Invar Behavior in Pd3Fe," was published in the June 12 issue of PRL. In addition to Winterrose and Fultz, the coauthors are Matthew S. Lucas, Alan F. Yue, Itzhak Halevy, Lisa Mauger, and Jorge Munoz (from Caltech); Jingzhu Hu, from the University of Chicago; and Michael Lerche, from the Carnegie Institution for Science.

The work was supported by the Carnegie–Department of Energy (DOE) Alliance Center, funded by the DOE through the Stewardship Sciences Academic Alliance of the National Nuclear Security Administration, and by the DOE's Office of Science, Office of Basic Energy Sciences; by the National Science Foundation and its Consortium for Materials Properties Research in Earth Sciences (COMPRES); and by the W. M. Keck Foundation.

Visit the Caltech Media Relations website at http://media.caltech.edu.

Kathy Svitil | EurekAlert!
Further information:
http://www.caltech.edu

More articles from Physics and Astronomy:

nachricht Study offers new theoretical approach to describing non-equilibrium phase transitions
27.04.2017 | DOE/Argonne National Laboratory

nachricht SwRI-led team discovers lull in Mars' giant impact history
26.04.2017 | Southwest Research Institute

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Fighting drug resistant tuberculosis – InfectoGnostics meets MYCO-NET² partners in Peru

28.04.2017 | Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

 
Latest News

Wireless power can drive tiny electronic devices in the GI tract

28.04.2017 | Medical Engineering

Ice cave in Transylvania yields window into region's past

28.04.2017 | Earth Sciences

Nose2Brain – Better Therapy for Multiple Sclerosis

28.04.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>