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 [ Time:2013/10/8 ]
Probing Methane's Secrets: A Breakthrough in Study of Hydrocarbon Chemistry under Extreme Environments
Author :WANG Yuan

Recently, a breakthrough has been made by a team including ISSP researchers, led by Dr. Alexander Goncharov,  member of Center for Energy Matter in Extreme Environments (CEMEE), in study of carbon-hydrogen fluids in deep interiors of planets. The research team simulates the evolution of hydrocarbons occurring deep inside planets. The results of these laboratory experiments renew previous understanding about the nature and genesis of hydrocarbons in the Earth��s mantle. The relevant results have been published in a Nature group journal (Nature Communication 4, 2446 (2013)).
Hydrocarbons from the Earth make up the main parts of fossil energy what we humans depend upon for survival. However, the exhaustion of resources has become an important problem influencing the living environment of mankind. The study of the various materials  formed from carbon and hydrogen under high pressures and temperatures, simulating those found in the Earth's interior, helps scientists understand the chemical processes occurring deep inside planets, including Earth.

The team use resistively- and laser-heated diamond anvil cells to measure methane melting and chemical reactivity up to 80 GPa and 2,000 K. The methane melting curve and chemical reactivity of the C-H system are established through spectroscopic measurements to simulate the evolution of hydrocarbons in deep planetary interiors. It reveals that the melting point of CH4 is even lower than that of water (H2O) and ammonia (NH3), suggesting that methane is not a solid under any conditions met deep inside the Earth's mantle. As the temperature increases above about 1,200 K methane becomes more chemically reactive and partly disassociates into hydrogen and elementary carbon. While heavy hydrocarbons become apparent at pressures above 250, 000 times atmospheric pressure (25 GPa), indicating under deep mantle conditions the environment is likely methane poor. The exhibited chemical reactivity of methane has crucial effects on the formation of diamond in deep inside of Earth. The findings renew peoples's previous understanding about the matter of Earth's mantle originating from the experimental results of surface conditions. Therefore, the reassessment of the geophysical models of Uranus and Neptune with the help of new experimental results is reasonably suggested.

CEMEE is part of the Institute of Solid State Physics, Chinese Academy of Sciences situated in Hefei. Since the beginning of this year, CEMEE has recently completed an experimental platform to study energy matter at extreme conditions. It is comprised of a multitude of probing capabilities of the physical nature of energy matter in extreme environments including ultrahigh pressures, extreme low and high temperatures, and high magnetic field. The existing facilities include systems for in situ measurements of electrical conductivity, magnetic susceptibility, dielectric constant, optical and vibrational properties at extreme conditions. The service facilities include a laser drilling system, diamond anvil cells (DAC), sample preparation laboratory for DAC, in situ pressure adjustment and measurement capabilities in a wide range of temperature, a high-pressure low-temperature Raman spectroscopy system functional to super-low (down to 10 cm-1) frequencies with a variety of the laser excitation wavelengths through ultraviolet and near infrared, and a high temperature-pressure laser heating system. Currently, a gas loading system is being set up for accessing hydrostatic pressure conditions and loading gases like hydrogen and methane etc. The research platform will make CEMEE to become a world class research center for quantum and energy matter at extreme conditions.

                                  

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