Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

NASA experiments validate 50-year-old hypothesis

02.07.2003


NASA-funded researchers recently obtained the first complete proof of a 50-year-old hypothesis explaining how liquid metals resist turning into solids


The photo on the July cover of Physics Today shows a solid metal sample of titanium-zirconium-nickel alloy inside the Electrostatic Levitator at NASA’s Marshall Space Flight Center in Huntsville, Ala. Using electromagnetic energy to levitate the sample was crucial because stray contamination from containers causes crystals to form inside liquid metals, which ruins measurements on pure samples. (NASA/MSFC/Emmett Given)



The research is featured on the cover of the July issue of Physics Today. It challenges theories about how crystals form by a process called nucleation, important in everything from materials to biological systems.

"Nucleation is everywhere," said Dr. Kenneth Kelton, the physics professor who leads a research team from Washington University in St. Louis. "It’s the major way physical systems change from one phase to another. The better we understand it, the better we can tailor the properties of materials to meet specific needs," he said.


Using the Electrostatic Levitator at NASA’s Marshall Space Flight Center in Huntsville, Ala., Kelton’s team proved the hypothesis by focusing on the "nucleation barrier." German physicist Gabriel D. Fahrenheit, while working on his temperature scale, first observed the barrier in the 1700s. When he cooled water below freezing, it didn’t immediately turn into ice but hung around as liquid in a supercooled state. That’s because it took a while for all the atoms to do an atomic "shuffle" arranging in patterns to form ice crystals.

In 1950, Dr. David Turnbull and Dr. Robert Cech, researchers at the General Electric Company in Schenectady, N.Y., showed liquid metals also resist turning into solids. In 1952, physicist Dr. Charles Frank, of the University of Bristol in England, explained this "undercooling" behavior as a fundamental mismatch in the way atoms arrange themselves in the liquid and solid phases. Atoms in a liquid metal are put together into the form of an icosahedron, a pattern with 20 triangular faces that can’t be arranged to form a regular crystal.

"The metal doesn’t change to a solid instantly, because it costs energy for the atoms to move from the icosahedral formation in the liquid to a new pattern that results in a regular crystal structure in the solid metal," explained Kelton. "It’s like being in a valley and having to climb over a mountain to get to the next valley. You expend energy to get over the barrier to a new place," he said.

Frank didn’t know about quasicrystals, first discovered in 1984, and researchers didn’t have tools like NASA’s Electrostatic Levitator. Using electrostatic energy to levitate the sample was crucial, because stray contamination from containers cause crystals to form inside liquid metals, which would have ruined Kelton’s measurements on pure samples.

To measure atom locations inside a drop of titanium-zirconium-nickel alloy, the levitator was moved to the Advanced Photon Source at Argonne National Laboratory in Chicago. There, an energetic beam of X-rays was used to map the average atom locations as the metal turned from liquid to solid. The experiment was repeated several times, and the data definitively verified Frank’s hypothesis.

As the temperature was decreased to solidify the molten sample, an icosahedral local structure developed in the liquid metal. It cost less energy to form the quasicrystal, because it had an icosahedral structure. This caused the quasicrystal to nucleate first, even though it was less stable than the crystal phase that should have formed. The icosahedral liquid structure was therefore directly linked to the nucleation barrier, as proposed by Frank.

To prepare for an International Space Station experiment, the team is continuing levitator experiments. The new techniques being developed for these studies can be applied to solve advanced materials problems on Earth and for spacecraft applications.

"As NASA scientists develop advanced materials for rocket engines and spacecraft, our facility will be a technological tool they can use to characterize materials," said Dr. Jan Rogers, a Marshall Center scientist who assisted Kelton’s research team.

Kelton’s team at Washington University included Geun Wu Lee, a graduate student, and Anup Gangopadhyay, a research scientist; Jan Rogers, Tom Rathz and Mike Robinson, all of the Marshall Center; Robert Hyers, University of Massachusetts, Amherst; and Doug Robinson, Ames Laboratory, U.S. Department of Energy, Ames, Iowa.

Kelton conducts his research under NASA’s Materials Science Program managed by the Marshall Center. The research is funded by the Physical Science Research Program — part of NASA’s Office of Biological and Physical Research in Washington, D.C., the Marshall Center Director’s Discretionary Fund and Internal Research and Development funds from the Marshall Center’s Science Directorate.

A peer-reviewed article that discusses this work appeared in the May 16 issue of Physical Review Letters. The research was featured in the May 30 issue of Science.

Steve Roy | MSFC News Center
Further information:
http://www1.msfc.nasa.gov/NEWSROOM/news/releases/2003/03-104.html
http://www.nasa.gov

More articles from Physics and Astronomy:

nachricht Computer model predicts how fracturing metallic glass releases energy at the atomic level
20.07.2018 | American Institute of Physics

nachricht What happens when we heat the atomic lattice of a magnet all of a sudden?
18.07.2018 | Forschungsverbund Berlin

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: Future electronic components to be printed like newspapers

A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.

The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

A smart safe rechargeable zinc ion battery based on sol-gel transition electrolytes

20.07.2018 | Power and Electrical Engineering

Reversing cause and effect is no trouble for quantum computers

20.07.2018 | Information Technology

Princeton-UPenn research team finds physics treasure hidden in a wallpaper pattern

20.07.2018 | Materials Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>