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 Studying fundamental particles in materials
17.01.2017 | Max-Planck-Institut für Struktur und Dynamik der Materie

nachricht Seeing the quantum future... literally
16.01.2017 | University of Sydney

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: How gut bacteria can make us ill

HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host

Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...

Im Focus: Interfacial Superconductivity: Magnetic and superconducting order revealed simultaneously

Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.

While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...

Im Focus: Studying fundamental particles in materials

Laser-driving of semimetals allows creating novel quasiparticle states within condensed matter systems and switching between different states on ultrafast time scales

Studying properties of fundamental particles in condensed matter systems is a promising approach to quantum field theory. Quasiparticles offer the opportunity...

Im Focus: Designing Architecture with Solar Building Envelopes

Among the general public, solar thermal energy is currently associated with dark blue, rectangular collectors on building roofs. Technologies are needed for aesthetically high quality architecture which offer the architect more room for manoeuvre when it comes to low- and plus-energy buildings. With the “ArKol” project, researchers at Fraunhofer ISE together with partners are currently developing two façade collectors for solar thermal energy generation, which permit a high degree of design flexibility: a strip collector for opaque façade sections and a solar thermal blind for transparent sections. The current state of the two developments will be presented at the BAU 2017 trade fair.

As part of the “ArKol – development of architecturally highly integrated façade collectors with heat pipes” project, Fraunhofer ISE together with its partners...

Im Focus: How to inflate a hardened concrete shell with a weight of 80 t

At TU Wien, an alternative for resource intensive formwork for the construction of concrete domes was developed. It is now used in a test dome for the Austrian Federal Railways Infrastructure (ÖBB Infrastruktur).

Concrete shells are efficient structures, but not very resource efficient. The formwork for the construction of concrete domes alone requires a high amount of...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

12V, 48V, high-voltage – trends in E/E automotive architecture

10.01.2017 | Event News

2nd Conference on Non-Textual Information on 10 and 11 May 2017 in Hannover

09.01.2017 | Event News

Nothing will happen without batteries making it happen!

05.01.2017 | Event News

 
Latest News

How gut bacteria can make us ill

18.01.2017 | Life Sciences

On track to heal leukaemia

18.01.2017 | Health and Medicine

Water - as the underlying driver of the Earth’s carbon cycle

17.01.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>