At the extreme pressure at the bottom of the Earth’s outer core, iron takes on a stronger form to handle the pressure in a process called “twinning”.
This is the result of a study conducted by researchers from the SLAC National Accelerator Laboratory that recreates cardiac pressure in the laboratory.
They do this by shining a laser beam on a sample of iron as wide as a human hair. The first creates a shock wave that quickly heats and presses the metal.
The second laser – part of the Linac Coherent Light source SLAC – allowed the team to investigate the effects on the atomic structure of iron in a millionth of a second.
At the extreme pressure at the bottom of the Earth’s outer core (shown in the technical clip above), iron takes on a stronger form to handle the pressure in a process called “twinning”. This is the result of a study conducted by researchers from the SLAC National Accelerator Laboratory that recreates cardiac pressure in the laboratory.
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Most of the metal you might encounter outside – whether in buildings, machinery, Victorian lamp posts for example, etc. – has a structure crystallologists call a ‘body-centered cube’.
This means that the crystal lattice is arranged in a nanocube pattern, with an iron atom in the center of each cube, as well as each of the eight corners.
When iron is subjected to higher stresses, this structure changes – taking, at over 10 gigapascals, a hexagonal shape that allows the atoms to stick together more tightly.
In their study, study author and geologist Arianna Gleeson of SLAC and her colleagues wanted to know what would happen to a packed iron hexagon if you continued to build pressure all the way to the Earth’s core.
“We’re not actually creating the conditions for the inner core, but we’re creating the conditions for the planet’s outer core — which is really cool,” Professor Gleason said.
The team wasn’t sure how iron would respond to such extreme conditions – about 360 million times the pressure at Earth’s surface and heat at the Sun’s surface – as never before observed.
It turns out that iron undergoes other structural transitions, such as the transition from the cubic to the hexagonal shape it undergoes at much lower stresses.
“When we keep pushing it, the iron doesn’t know what to do with the extra pressure,” Professor Gleeson explains.
“He needs to take that pressure off, so he’s trying to find the most efficient mechanism to do that.”
The iron handling mechanism – its twin – sees the atomic arrangement tilted sideways, and all the hexagonal prisms rotate about 90 degrees.
Twins are a common stress response in many minerals and minerals, including calcite, quartz, titanium, and zirconium.
Professor Gleasonsaid said: “Twinning allows iron to become very strong – stronger than we thought – before starting to flow plastically over a longer time scale.[daripada sebaliknya]“[daripadasebaliknya’kataProfesorGleason[thanitwouldhaveotherwise’ProfessorGleasonsaid][fromthecontrary’saidProfessorGleason[مماكانيمكنأنيحدثبطريقةأخرى”[daripadasebaliknya’kataProfesorGleason[مماكانيمكنأنيحدثبطريقةأخرى”[daripadaseharusnyasebaliknya’ProfesorGleasonberkata[daripadasebaliknya’kataProfesorGleason[مماكانيمكنأنيحدثبطريقةأخرى”[thanitwouldhaveotherwise’ProfessorGleasonsaid
“When we keep pushing it, the iron doesn’t know what to do with the extra pressure,” Professor Gleeson explains. “He needs to take that pressure off, so he’s trying to find the most effective mechanism to do that.” Iron countermeasures – twinning – see the atomic arrangement tilted to the side, rotating the hexagonal prism about 90 degrees
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“Now we can give a thumbs up, and a thumbs up at some physical models for very basic deformation mechanisms,” said Professor Gleason.
This helps build some predictive power that we don’t have for modeling how materials will respond under extreme conditions.
In addition, the team explains, the same method could be applied to better understand how other materials behave under extreme conditions.
Prior to conducting the experiment, the researchers weren’t sure whether iron would respond too quickly to measure or too slowly to see.
“The fact that twinning occurs on a time scale that we can measure is an important result,” explains the paper’s author and geophysicist Sebastian Merkel of the University of Lille in France.
Twins are a common stress response in many minerals and minerals, including calcite, quartz, titanium, and zirconium. Photo: twin quartz crystal
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“The future is bright now that we have developed a way to make these measurements,” Professor Gleeson added, also noting that recent upgrades to the Linac Coherent Light Source will allow the material to be studied at higher X-ray energies.
He explains that this will allow the study of ‘alloys, thicker materials with lower symmetry and more complex X-ray fingerprints’ – while also enabling observations of larger samples, allowing for a more comprehensive look at the behavior of iron.
Further, Gleeson said, “We will acquire a more powerful optical laser with agreement to move forward with the new pilot petawatt laser facility.
He concluded, “This will make future work more interesting because we will be able to access the basic internal conditions of the Earth without any problems.”
The full results of this study are published in the journal physical review message.
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