Researchers shed light on physical properties of carbon at extreme conditions

January 24, 2006
Graphic simulation of the electronic wave function (MLWF) in liquid carbon
Graphic simulation of the electronic wave function (MLWF) in liquid carbon at a temperature of 9,000°Kelvin and five million atmospheres of pressure, showing a persistent covalent bonding even under these extreme conditions. At this pressure diamond melts at about 8,000°K.

A team based in Livermore has shed some light on the phase diagram of carbon at high pressure and temperature. In particular, the authors determined the solid/liquid and solid/solid phase boundaries for pressures up to 20 million atmospheres and more than 10,000 degrees Kelvin.

The simulations provide results on the physical properties of carbon, which are of great importance for devising models of Neptune, Uranus and white dwarf stars, as well as of extrasolar carbon-rich planets.

In its elemental form, carbon is found in coal, graphite, diamond, bucky balls and nanotubes. These are materials with very different properties, yet at the microscopic level they only differ by the geometrical arrangements of carbon atoms.

Elemental carbon has been known since prehistory, and one of its best known forms, diamond, is thought to have been first mined in India more than 2,000 years ago. The properties of diamond and its practical and technological applications have been extensively investigated for many centuries.

In spite of many investigations over centuries, and of important experimental work of the last decades aimed at studying compressed diamond, the phase boundaries and melting properties of elemental carbon are poorly known, and its electronic properties are not well understood under extreme conditions. Experimental data are scarce because of difficulties in reaching megabar (1 million atmospheres) pressures and thousands of Kelvin regimes in the laboratory.

The team is composed by Alfredo Correa, Stanimir Bonev and Giulia Galli who all were at the Lawrence Livermore Laboratory at the time this work started. Galli is now a professor at UC Davis and Bonev is an assistant professor at Dalhousie University, in Canada.

"Our results show a consistent description of elemental carbon in a broad range of temperature and pressures and a description of its electronic properties within the same framework," said Correa, a Student Employee Graduate Research Fellowship (SEGRF) student from UC Berkeley who works in the Laboratory's Quantum Simulations Group in the Physics and Advanced Technology Directorate. Correa is the lead author of a paper on the recent findings that appears in the online version of the Proceedings of the National Academy of Sciences for the week of Jan. 23-27.

The researchers also discovered that the diamond/BC8/liquid triple point (the temperature and pressure at which these three phases coexist in thermodynamic equilibrium) is at a lower pressure than previously thought (BC8 denotes a solid phase of carbon which diamond transforms into above 12 Mbar, at zero temperature;). The conditions at which the triple point is found are close to recent estimates of the core conditions (temperature and pressure) in Neptune and Uranus.

"Our simulation results call for a partial revision of current planetary models, especially for the description of their core regions," Correa said. "Our computational work also may help us interpret future experimental work."

Source: Lawrence Livermore National Laboratory

Explore further: New form of carbon that's hard as a rock, yet elastic, like rubber

Related Stories

New method of characterizing graphene

May 30, 2017

Scientists have developed a new method of characterizing graphene's properties without applying disruptive electrical contacts, allowing them to investigate both the resistance and quantum capacitance of graphene and other ...

CO2 clathrate hydrate properties

March 30, 2017

Clathrate hydrates (Fig. 1) are cage-like structures of water molecules that house guest gas species. They form when the gas interacts with ice under high-pressure and low-temperature conditions, and are thought to influence ...

Recommended for you

Biofilms—the eradication has begun

June 22, 2017

Have you ever heard of biofilms? They are slimy, glue-like membranes that are produced by microbes, like bacteria and fungi, in order to colonize surfaces. They can grow on animal and plant tissues, and even inside the human ...

UN says world population will reach 9.8 billion in 2050

June 22, 2017

India's population is expected to surpass China's in about seven years and Nigeria is projected to overtake the United States and become the third most populous country in the world shortly before 2050, a U.N. report said ...

Problem of wheeled suitcases wobbling explained

June 21, 2017

(—A team of researchers at Universite Paris-Diderot has uncovered the reason for wobbling of wheeled suitcases. In their paper published in Proceedings of the Royal Society A, the group explains the physics behind ...

Chemists create 3-D printed graphene foam

June 21, 2017

Nanotechnologists from Rice University and China's Tianjin University have used 3-D laser printing to fabricate centimeter-sized objects of atomically thin graphene.


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.