Iron is an essential component of many specialized materials. In research, we subject it to extreme conditions daily to observe how it reacts — this helps us learn more about the material’s properties and gives us insight into how it can be used to our advantage. It has not been previously studied how iron reacts to extreme pressures, specifically pressure that is close to what it experiences at the Earth’s core.
The Earth’s core is almost entirely made up of iron and nickel. It has a radius of about 2,165 miles (but this has only been estimated since It’s currently impossible to take measurements of the core). The pressure in the Earth’s core is a whopping 3.6 million atmosphere (atm). To give this some perspective, humans experience 1 atm at sea level.
Researchers at the SLAC National Accelerator Laboratory at Stanford University have recreated the immense pressure of the Earth’s core to observe how iron reacts in this environment.
To simulate the pressure of the Earth’s core, the researchers used two lasers— one to generate the pressure and one to observe. The first laser fired a pulse that sent a shockwave through the iron sample, and the second laser used x-ray diffraction to capture a single femtosecond snapshot of the iron crystal. A femtosecond is 10-15 seconds.
By varying the times, the snapshot was taken over multiple laser pulses, researchers could put together something like a stop-motion film that showed the iron sample’s reaction to the pulses. When the measurements were all taken, the researchers observed something unique: the iron underwent twinning.
Twinning is a common occurrence in many metals. It is a process of reformation that allows metals to withstand high pressure. Iron atoms self-arrange into cubes, and when pressure is applied, the atoms rearrange into hexagonal prisms. This allows the iron to withstand the higher pressure. Under extreme pressure, the iron undergoes twinning, which helps the iron become even more durable. Half of the prism rotates 90°, so the iron ends up as two crystals connected at a right angle. Twinning of the iron crystals was also observed even after the pressure decreased.
While researchers couldn’t achieve the same pressure found in the inner core, they got pretty close. No one has studied how iron reacts to these extreme pressures or temperatures, so the researchers didn’t have any evidence to suggest how the iron would respond. This research shows promising evidence of how iron reacts at the Earth’s core and gives scientists further insight into the metal’s properties. The methods used in this experiment are important as well, because they can be used to study other materials and how they react to extreme stress.