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 Transportable laser
23.01.2018 | Physikalisch-Technische Bundesanstalt (PTB)

nachricht New for three types of extreme-energy space particles: Theory shows unified origin
23.01.2018 | Penn State

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: Optical Nanoscope Allows Imaging of Quantum Dots

Physicists have developed a technique based on optical microscopy that can be used to create images of atoms on the nanoscale. In particular, the new method allows the imaging of quantum dots in a semiconductor chip. Together with colleagues from the University of Bochum, scientists from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute reported the findings in the journal Nature Photonics.

Microscopes allow us to see structures that are otherwise invisible to the human eye. However, conventional optical microscopes cannot be used to image...

Im Focus: Artificial agent designs quantum experiments

On the way to an intelligent laboratory, physicists from Innsbruck and Vienna present an artificial agent that autonomously designs quantum experiments. In initial experiments, the system has independently (re)discovered experimental techniques that are nowadays standard in modern quantum optical laboratories. This shows how machines could play a more creative role in research in the future.

We carry smartphones in our pockets, the streets are dotted with semi-autonomous cars, but in the research laboratory experiments are still being designed by...

Im Focus: Scientists decipher key principle behind reaction of metalloenzymes

So-called pre-distorted states accelerate photochemical reactions too

What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...

Im Focus: The first precise measurement of a single molecule's effective charge

For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.

Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...

Im Focus: Paradigm shift in Paris: Encouraging an holistic view of laser machining

At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.

No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

10th International Symposium: “Advanced Battery Power – Kraftwerk Batterie” Münster, 10-11 April 2018

08.01.2018 | Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

 
Latest News

Rutgers scientists discover 'Legos of life'

23.01.2018 | Life Sciences

Seabed mining could destroy ecosystems

23.01.2018 | Earth Sciences

Transportable laser

23.01.2018 | Physics and Astronomy

VideoLinks Science & Research
Overview of more VideoLinks >>>