Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


NASA experiments validate 50-year-old hypothesis


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:

More articles from Physics and Astronomy:

nachricht Physicists made crystal lattice from polaritons
20.03.2018 | ITMO University

nachricht Mars' oceans formed early, possibly aided by massive volcanic eruptions
20.03.2018 | University of California - Berkeley

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: Mars' oceans formed early, possibly aided by massive volcanic eruptions

Oceans formed before Tharsis and evolved together, shaping climate history of Mars

A new scenario seeking to explain how Mars' putative oceans came and went over the last 4 billion years implies that the oceans formed several hundred million...

Im Focus: Tiny implants for cells are functional in vivo

For the first time, an interdisciplinary team from the University of Basel has succeeded in integrating artificial organelles into the cells of live zebrafish embryos. This innovative approach using artificial organelles as cellular implants offers new potential in treating a range of diseases, as the authors report in an article published in Nature Communications.

In the cells of higher organisms, organelles such as the nucleus or mitochondria perform a range of complex functions necessary for life. In the networks of...

Im Focus: Locomotion control with photopigments

Researchers from Göttingen University discover additional function of opsins

Animal photoreceptors capture light with photopigments. Researchers from the University of Göttingen have now discovered that these photopigments fulfill an...

Im Focus: Surveying the Arctic: Tracking down carbon particles

Researchers embark on aerial campaign over Northeast Greenland

On 15 March, the AWI research aeroplane Polar 5 will depart for Greenland. Concentrating on the furthest northeast region of the island, an international team...

Im Focus: Unique Insights into the Antarctic Ice Shelf System

Data collected on ocean-ice interactions in the little-researched regions of the far south

The world’s second-largest ice shelf was the destination for a Polarstern expedition that ended in Punta Arenas, Chile on 14th March 2018. Oceanographers from...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

Virtual reality conference comes to Reutlingen

19.03.2018 | Event News

Ultrafast Wireless and Chip Design at the DATE Conference in Dresden

16.03.2018 | Event News

International Tinnitus Conference of the Tinnitus Research Initiative in Regensburg

13.03.2018 | Event News

Latest News

Physicists made crystal lattice from polaritons

20.03.2018 | Physics and Astronomy

Mars' oceans formed early, possibly aided by massive volcanic eruptions

20.03.2018 | Physics and Astronomy

Thawing permafrost produces more methane than expected

20.03.2018 | Earth Sciences

Science & Research
Overview of more VideoLinks >>>