From: Andy Soos, ENN
Published July 7, 2010 03:33 PM

Really High Pressures

Deep down in the earth are tremendously high pressures. What happens under high pressure is not the same as what happens at lower pressures. Lawrence Livermore National Laboratory physicists are using an ultra fast laser based technique they dubbed nanoshocks for something entirely different. In fact, the nanoshocks have such a small spatial scale that scientists can use them to study shock behavior in tiny samples such as thin films or other systems with microscopic dimensions (a few tens of micrometers). In particular they have used the technique to shock materials under high static pressure in a diamond anvil cell.

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The Earth’s mantle is mostly solid and overlies the Earth’s iron rich core. The lower mantle, which makes up more than half of the Earth by volume, is subject to high pressure temperature conditions with a mineral collection made mostly of ferropericlase and silicate perovskite. The Earth’s lower mantle varies in pressure from 220,000 atmospheres) to 1,400,000 atmospheres. These cannot be directly studied and can only be stimulated and tested in the laboratory.

Using a cell, which probes the behavior of materials under ultra high pressures, the team statically compressed a sample of argon up to 78,000 atmospheres of pressure and then further shock compressed it up to a total of 280,000 atmospheres. They analyzed the propagating shock waves using an ultra fast interferometric technique. They achieved combinations of pressures, temperatures and time scales that are otherwise inaccessible.

In comparison the pressure at the center of the earth is estimated as 3.6 million atmospheres. A typical explosion may cause a peak pressure wave of 0.5 atmospheres (to shatter a brick wall) or higher.

Study of high pressure mechanics and effects are useful in studying detonations, material design, and the seismic actions of the earth that eventually effect tectonic movement and volcanic action.

“It can be used to study fundamental physical and chemical processes as well as improve our understanding of a wide range of real world problems ranging from detonation phenomena to the interiors of planets, " said  physicist Jonathan Crowhurst, a co-author of a paper, which will appear in the July 15 edition of the Journal of Applied Physics.

“Essentially, this allows us to examine a very broad range of thermodynamic states, including states corresponding to planetary interiors and high density, low temperature states that have been predicted to exhibit unobserved exotic behavior,"  Michael Armstrong, another co-author, said.

For decades, compression experiments have been used to determine the thermodynamic states of materials at high pressures and temperatures. The results are necessary to correctly interpret seismic data, understand planetary composition and the evolution of the early solar system, shock wave induced chemistry and fundamental issues in condensed matter physics.

For further information: https://publicaffairs.llnl.gov/news/news_releases/2010/NR-10-07-01.html

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