Summary Points
- Diamonds can melt under extreme pressure, maintaining their crystal structure until melting.
- Recent experiments revealed lower melting temperatures at terapascal pressures, aligning with theories.
- No evidence found for the predicted BC8 phase; diamond melts before transforming.
- Melting diamond under these conditions causes it to behave like ice, floating in liquid carbon.
Scientists Discover Diamond Can Melt Under Extreme Conditions
Scientists have taken another step in understanding how materials behave under intense pressure. A team led by Marius Millot at Lawrence Livermore National Laboratory (LLNL) used powerful lasers to compress tiny diamond samples. They created pressures higher than the center of Neptune and temperatures hotter than the surface of the Sun. Surprisingly, the diamond remained in its crystal form until it suddenly melted, without transforming into other known carbon phases.
Previous experiments suggested diamonds might change forms before melting, but newer technology showed otherwise. Using advanced X-ray imaging, the team saw that diamond stays in its familiar cubic structure until the moment it turns into liquid carbon. The temperature at which it melts is about 7,300 Kelvin—much lower than earlier measurements. This new data matches better with theoretical calculations, solving a long-standing puzzle in high-pressure physics.
The experiments also revealed an unusual property: solid diamond becomes less dense than liquid carbon at these conditions. This means, under extreme pressure, diamond could float in its molten form, similar to how ice floats on water. Moreover, increasing pressure can actually lower the melting point during certain stages, which is quite counterintuitive and also observed in ice.
These findings are important for understanding giant planets like Uranus and Neptune, where similar extreme conditions exist. Closer to Earth, knowing how diamond behaves at high pressure helps improve nuclear fusion models. Better data can lead to safer, more efficient fusion energy, potentially boosting power output. Millot’s team notes that these insights could allow for slower shocks in fusion experiments, increasing energy yield without extra energy input. The research was published in Nature Physics.
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