Scientists have been able to synthesize iron in a form that is found deep in the Earth’s core
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Scientists have succeeded in synthesizing iron in a form that is deep in the Earth’s core. For this, they used an experimental approach. This study was described in detail in the journal Physical Review Letters. The resulting form is called hexaferrum or epsilon iron (ϵ-Fe). It remains stable only under extremely high pressure. Researchers believe that this is the majority of iron in the Earth’s core. But it is difficult to reproduce the same conditions on the surface. Photo: Diagram illustrating the compression of iron in a diamond anvil to produce hexaferrium (APS/C. Cain; S. Deemyad/University of Utah) In an effort to better understand the composition of the nucleus, scientists turned to all known knowledge. In particular, we had to rely on seismological data. Studies have shown that the Earth’s core is solid and surrounded by liquid. However, there were still questions. In the 20th century found out that seismic waves spread faster from pole to pole and from equator to equator. Therefore, most theories explained it by the probable structure of iron in the core. But it was difficult to reliably verify this on the surface due to destruction during synthesis. The problem was the transformation of an atmospheric pressure phase of iron called ferrite, or alpha iron. Usually, when high pressure is applied to ferrite in an attempt to grind it into hexaferrium, it breaks into tiny crystals unsuitable for detailed analysis, which frustrates attempts to study its properties. So a group of physicists led by Agnes Devaillet solved the problem step by step. First, they placed ferrite crystals in a diamond anvil in a vacuum heater, increasing the pressure to 7 gigapascals – a pressure 70,000 times greater than the atmospheric pressure of the sea – and the temperature to 800 Kelvin (527 degrees Celsius). This helped create austenite, an intermediate phase of iron. It differs from ferrite, and its crystals transitioned much more smoothly into the hexaferrum phase at a pressure of 15 to 33 gigapascals at 300 Kelvin. The synchrotron beam of the European Synchrotron Radiation Center was used to study hexaferrium. The work of Devaillet and her team showed that the elasticity of hexaferrium depends on the direction; waves propagate faster along one particular axis. This phenomenon also persists during changes in pressure, which indicates that hexaferrium behaves in the same way in an environment up to 360 gigapascals of the inner core. This is consistent with observations of how seismic waves travel across the planet. The scientists believe that the findings suggest that the team’s methods could be an excellent probe for understanding the extreme conditions at the center of our world. Earlier we wrote that scientists discovered a solid iron core in the structure of the Moon. Read also: Scientists have announced the beginning of a new geological era of the Earth
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