Researchers recreate deep-earth conditions to test stress impact on iron
Iron’s response to stress under such high temperatures and pressures had never been measured to this extent before, leaving researchers puzzled as to how the iron would react.
Researchers recreate deep-Earth conditions to see how iron copes with extreme stress.
(photo credit: Greg Stewart/SLAC National Accelerator Laboratory.)
Researchers aimed to discover what would happen to iron at the Earth's core in a study by Stanford University’s SLAC National Accelerator Laboratory.
The study, which was published in the peer-reviewed scientific journal Physical Review Letters,
used lasers in order to study the effects of iron in conditions similar
to those in earth’s core, which reaches temperatures of about 5,200°
Celsius (9,392° Fahrenheit), according to National Geographic.
The group at SLAC wanted to see what would happen if you kept applying
pressure to a hexagonal arrangement of iron atoms to mimic what happens
to iron at the Earth's core or during atmospheric reentry from space.
Using two lasers, an optical laser and the SLAC's Linac Coherent Light
Source (LCLS) X-ray free-electron laser. The optical laser allows
researchers to expose the iron sample to extremely high temperatures and
the LCLS laser allows researchers to observe the iron on an atomic
level.
“At the time, LCLS was the only facility in the world where you could do
that," says study co-author Sébastien Merkel of the University of Lille
in France. "It's been a door opener for other similar facilities in the
world."
"We didn't quite make inner core conditions," study co-author
Arianna Gleason, a scientist in the High-Energy Density Science (HEDS)
Division at SLAC, told the American Association for the Advancement of
Science (AAAS). "But we achieved the conditions of the outer core of the
planet, which is really remarkable."
Earth photo cutaway with core. (credit: VIA WIKIMEDIA COMMONS)
Iron’s
response to stress under such high temperatures and pressures had never
been measured to this extent before, leaving researchers puzzled as to
how the iron would react.
"As
we continue to push it, the iron doesn't know what to do with this
extra stress," says Gleason. "And it needs to relieve that stress, so it
tries to find the most efficient mechanism to do that."
The
team fired both lasers at a tiny sample of iron about the width of a
human hair. "The control room is just above the experimental room,"
Merkel says. "When you trigger the discharge, you hear a loud pop."
The iron atoms eventually began “twinning” under the pressure. The
anatomical arrangement rotates all the hexagonal prisms of iron atoms by
nearly 90 degrees. Twinning is a common pressure response in metals and
minerals — quartz, titanium and zirconium all undergo twinning.
“Twinning allows iron to be incredibly strong — stronger than we first
thought — before it starts to flow plastically on much longer time
scales,” Gleason said.
The
researchers measured the transformation by collecting images and
assembled them into a flipbook that showed iron deforming. Researchers
were previously unsure if iron would respond too fast for them to
measure or too slow for them to ever see. "The fact that the twinning
happens on the time scale that we can measure it as an important result
in itself," explained Merkel.
The study provides
exciting insights into the structural properties of iron at extremely
high temperatures and pressures. The results are also a promising
indicator that these methods could help scientists understand how other
materials behave within extreme conditions as well. "The future is bright now that we've developed a way to make these measurements," Gleason said.
"Now
we can give a thumbs up, thumbs down on some of the physics models for
really fundamental deformation mechanisms," Gleason continued. "That
helps to build up some of the predictive capability we're lacking for
modeling how materials respond at extreme conditions."
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