Carbon dioxide forms polymeric materials under high pressure

Mar 25, 2009

Carbon dioxide is a molecular gas at ambient conditions and an important consitituent of the Earth’s atmosphere. It is also a likely component in the Earth’s mantle, and it plays an important role in the life cycle. But at high pressure, carbon dioxide can transform to a solid.

The commonly known solid-state form of is the so called 'dry ice', which is a molecular crystal and has many important applications, e.g. food producation and storage, artificial fog in theatre and artificial rainfall, etc. Even more interesting, as the pressure increases and varies, the intra- and inter-molecular interactions of carbon dioxide change dramatically and this results in different crystal structures in polymeric dense phases with interesting physical properties, such as “super-hardness”. Thus carbon dioxide has become an extremely hot topic in science in the last decade.

Recently, a collaborative study between the research groups in Canada, Germany, Slovakia, Italy and USA achieved progress on this highly interested compound. Using  a novel computer-based simulation method called metadynamics combined with accurate quantum mechanical calculations, they found that a molecular solid called CO2-II transfers to a layered polymeric structure at a pressure of 60 GPa (1 GPa is approximately 10000 atmospheres) and temperature at 600 Kelvin.

Based on the good agreement between their calculated Raman spectra and X-ray diffraction patterns and the previous experimental values, a new interpretation of a previous experimental result is given. A recently identified VI found in experiment, assumed to be disordered stishovite-like structure, is instead interpreted as the result of an incomplete transformation from the molecular phase into a final layered polymeric structure. In addition, a new α-cristobalite-like CO2 as found in silicon dioxide, is predicted to be formed from CO2-III via an intermediate structure at 80 GPa and temperature lower than room temperature. Defects in the crystals increase with temperature and CO2 transforms to an amorphous form when temperature is higher than room temperature, consistent with previous experiments.

These results obtained from fully dynamical simulations reveal hitherto unknown microscopic transformation mechanisms, and illustrate the transformation from a molecular solid characterized by only intra-molecular bonding to a polymerized structure. The transformation takes place at pressures within the range found in the Earth’s mantle, where a significant amount of oxidized carbon is thought to be present, either in the form of carbonates or as a fluid. The large and abrupt changes in the bonding properties of CO2 reported here hint to possible discontinuities in the carbon chemistry of the mantle. Their article by Dr. Jian Sun et al. has been published in Proceedings of the National Academy of Sciences.

More information: Jian Sun, Dennis D. Klug, Roman Martonak, Javier Antonio Montoya, Mal-Soon Lee, Sandro Scandolo and Erio Tosatti: High-pressure polymeric phases of carbon dioxide. In: PNAS early edition, www.pnas.org_cgi_doi_10.1073_pnas.0812624106

Provided by Ruhr-Universitaet-Bochum

Explore further: Synthesis of a new lean rare earth permanent magnetic compound superior to Nd2Fe14B

add to favorites email to friend print save as pdf

Related Stories

Polymeric nitrogen synthesised

Aug 05, 2004

The new single-bonded nitrogen phase could serve as a high-energy storage material, report Max Planck researchers in Mainz, Germany Nitrogen, the major constituent of air, usually consists of inert molecul ...

Miniature Gas Tank

Jan 28, 2005

Porous networks of organic Van der Waals crystals can selectively store methane and carbon dioxide Washing powders are generally known to consist partially of inorganic zeolites. These aluminosilicates form porous structure ...

An Inexhaustible Source of Energy from Methane in Deep Earth

Sep 15, 2004

Untapped reserves of methane, the main component in natural gas, may be found deep in Earth’s crust, according to a recently released report in the Proceedings of the National Academy of Sciences of the United States of America ...

Recommended for you

Scientists develop compact medical imaging device

4 hours ago

Scientists at the MIRA research institute, in collaboration with various companies, have developed a prototype of a handy device that combines echoscopy (ultrasound) with photoacoustics. Combining these two ...

User comments : 0