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Our research focuses on understanding the large-scale behavior of planetary interiors through direct examination of the properties of materials under extreme conditions of pressure and temperature. The geological activity at the Earth's surface, which can so profoundly affect humanity, has its origins in processes ongoing in the deep interior. We wish to understand in detail the processes which control the evolution, dynamic behavior, and structure of the Earth and other planets. Recent efforts in this area have concentrated on measuring elastic properties of silicate minerals at pressures corresponding to the transition zone of the Earth's mantle. These measurements, when combined with high-resolution seismic data, provide a direct test of models of upper mantle mineralogy. The application of high pressure can produce large changes into interatomic forces, bonding properties, and the crystal structure of materials. The transformation of graphite to diamond by application of high pressure and temperature is a common example of the type of profound changes induced by pressure. Using the diamond anvil cell, we have compressed earth materials to static pressures more than two million times greater than atmospheric pressure. With laser heating techniques, it is possible to simultaneously heat the material to temperatures exceeding those in the Earth's mantle. Studies of this type provide fundamental insight into thermodynamic, chemical, and physical properties of matter under conditions of the Earth's mantle and core. Recent experimental efforts have focused on understanding the phase diagram of iron and ther transition metals such as cobalt. The high pressure-temperature phase relations and melting behavior of iron are crucial for understanding core formation in the Earth and for constraining the temperature distribution within the planet. X-ray diffraction is a powerful technique for probing the extreme states of matter achieved using the laser-heated diamond anvil cell. Unfortunately, conventional laboratory x-ray sources provide insufficient flux for many high-pressure experiments of interest. Prof. Duffy has recently worked on developing a high-pressure research facility at the Advanced Photon Source, a new synchrotron x-ray facility at Argonne National Laboratory. The development of a new generation of synchrotron x-ray facilities promises to greatly expand the range and accuracy of experiments that can be performed under very high external pressures. |
HighlightsSeptember 2008: Welcome to Jue Wang, new 1st year graduate student! March 2008: Suki Dorfman joins the Mbar club. Congratulations to Zhu Mao who has received a Best Student Paper award for her presentation on: Single-crystal elasticity of hydrous wadsleyite to 12 GPa at the Fall 2007 American Geophysical Union Meeting in San Francisco! Article by Tom Duffy on deep mantle mineralogy in Nature's Year of Planet Earth Special Issue |
This picture shows a sample contained within a diamond anvil cell. The sample is the mineral hematite (Fe2O3), which is contained within a 100 micron diameter hole in the surrounding steel gasket. This sample is at a pressure of 60 GPa (600 kilobars) which corresponds to the lower mantle of the Earth (see below). For more details about the diamond cell, follow the link for lab tour.
The figure shows some of the main features of the internal structure of the Earth (from Lamb and Sington, "Earth Story"). The pressure at the core-mantle boundary is 135 GPa, while that at the center of the Earth is 363 GPa. This entire pressure can be accessed using the diamond anvil cell. By combining with new laser heating techniques, the entire temperature range found in the Earth's interior can also be reproduced in the laboratory.