A new study has improved understanding of the diamond melting process, which may also be relevant to achieving higher energy gains in laser-based nuclear fusion.
Researchers at Lawrence Livermore National Laboratory (LLNL) document how diamonds melt under pressures three times greater than conditions found in the Earth’s core.
“We were able to take small samples of diamond and shock-pressure them to temperatures higher than the surface of the Sun and to pressures higher than the centers of Neptune and Uranus – and still measure atomic structure, temperature, density and optical reflectivity,” said author and LLNL scientist Marius Milot.
Applying the results to inertial confinement fusion could result in a three-fold increase in energy
The study resolves two long-standing contradictions in the field, finally matching experimental results to simulations based on quantum mechanics. Applying the results to inertial fusion can be tripled energy Gains and new understanding of the high-pressure phases of diamond could reshape models of planetary interior design. according to press release.
The researchers also highlighted that diamonds are more than just a dazzling gem – the extremely hard carbon forms the grain that encases the fuel needed for inertial fusion, and scientists believe it rains down deep within icy giant planets like Neptune and Uranus. In both cases, the material is subjected to enormous pressures. So far, experiments and simulations have differed on how they actually behave under those conditions.
The team also noted that LLNL has been studying the extreme behavior of diamonds for decades. Laboratory scientist John Eggert and his colleagues pioneered high-pressure melting experiments about 20 years ago, when they noticed that the density of diamonds increased when melted.
“Although this is unusual among most materials, we all know an example of this behavior,” said LLNL scientist Marius Mellot.
“Liquid water is denser than ice, which makes ice cubes float. John’s discovery means that diamonds will float in liquid carbon at high pressures.”
Although this work was a landmark in the field, it led to more questions. One factor in particular stunned the research community: There was about a 20% difference between observed and predicted diamond melting temperatures.
“No matter what theorists did, even with the most advanced computer simulation techniques, they couldn’t reproduce the experiments,” Milo said.
Published in Nature, AL He studies It resolves the discrepancy between experiments and theoretical simulations of the melting temperature of diamond, and shows that the diamond structure persists up to 1 TPa. This contradicts a previous report of a transition to the BC8 phase, which density functional theory predicts is the thermodynamically stable phase of carbon above pressures of about 1 TPa.
The results provide evidence of shock-induced melting
The results of the study provide evidence of shock-induced melting with a slight decrease in the melting temperature with increasing pressure near 7300 K.
“Our work provides atomic-level standards for quantum simulations of condensed matter at extreme conditions, with implications for planetary interiors. Our improved understanding of diamond melting may also be relevant to achieving higher energy gains in laser-driven nuclear fusion,” the researchers said.
