Diamond is traditionally considered the hardest natural substance on Earth and is often perceived as something that never melts. However, under extreme conditions, it is still subject to melting. Scientists recently conducted a new laser experiment that allowed them to obtain the most accurate data on the melting point of diamond, and the results were quite unexpected.
Previous studies indicated a temperature exceeding the actual one by 1300 degrees Fahrenheit, which represented an error of about 20 percent. The new measurement aligns with theoretical models and helps resolve a long-standing problem that has existed for two decades. This finding may play an important role in understanding nuclear fusion energy processes, as well as the internal structure of giant planets such as Uranus and Neptune.
The scientists directed powerful ultraviolet beams onto small plates of synthetic diamond. The shock waves generated by these beams were so strong that the diamond acquired a mirror-like luster, transitioning from a transparent state. The sharp change in luster served as an indicator of diamond melting. Researchers determined the temperature by measuring the reflection and luster of the diamond.
According to Marius Milot, a scientist from the Lawrence Livermore National Laboratory, they compressed diamond samples at temperatures exceeding the surface of the Sun and at pressures greater than those in the cores of Neptune and Uranus. Despite this, they managed to measure the density, temperature, and optical reflection of the atomic structure.
Furthermore, X-ray diffraction showed that before melting, the diamond did not undergo a transition into any other solid form. This is because rearranging atoms requires too much energy.
The difference between previous experiments and theoretical models was 2240 degrees Fahrenheit, and scientists had been trying to explain this discrepancy for two decades. The new experiment proved that the actual melting point of diamond is significantly lower than previously assumed. Diamond was found in the form of liquid carbon at pressures ranging from 660 to 1060 gigapascals and a temperature of 6727 degrees Celsius.
As pressure increases, the proportion of diamond transforming into liquid carbon increases. Liquid carbon is an unusual substance: it behaves like a metal, conducting electricity, and is also denser than diamond itself. If it could be placed in a cup, a piece of solid diamond could float in it, similar to an ice cube.
This data is extremely important for fusion research, as fusion is the process that powers stars and is a potential source of future energy. In many experiments, diamond capsules are heated and compressed by lasers to introduce deuterium and tritium at pressures exceeding 30 petapascals and temperatures over 100 million degrees Celsius.
Accurate knowledge of the temperature will make models more reliable and improve the results of fusion experiments. Similarly, it will help better understand the hypothesis of diamond rain and oceans of liquid carbon inside icy giants like Uranus and Neptune. Researchers believe that shock waves can sometimes transform diamond into another solid form, and understanding this is critically important for fusion experiments. Knowledge of how substances behave under such extreme conditions will open new horizons not only in energy research but also in astronomy and materials physics.