Physics
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmdi44a..07h&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #DI44A-07
Physics
3909 Elasticity And Anelasticity, 3919 Equations Of State, 3924 High-Pressure Behavior, 3949 Thermal Expansivity, 3954 X-Ray, Neutron, And Electron Spectroscopy And Diffraction
Scientific paper
With the maturing of laser heating systems for the diamond anvil coupled to 3rd generation synchrotron radiation sources, studies at high pressures are moving from end member to binary and even more complex systems. Interesting discoveries are being made, for instance the addition of Si to pure Fe stabilizes the bcc phase to exceptionally high pressures [Lin, et al., 2002, Science]. More recently Ni has been found to also stabilize the bcc structure of iron at pressures in excess of 200 GPa [Dubrovinsky, et al., 2007, Science]. Thus minor elements can significantly change the topology of phase diagrams. The observations of Lin et. al. sparked the interests of theorticians who modeled the effects of impurities [Vocadlo, et al., 2003, Nature]. Various compositions in the binary system Fe-FeS have been studied to 160 GPa and in the Fe-FeO system to 100 GPa. In addition to thermal equation of state data we have also collected melting data and subsolidus phase relations. This data provide information on how these candidate minerals would behave at the elevated temperatures and pressures, and thus have implications for the current state of the interior of terrestrial planets and their thermal evolution. On a lighter note (in terms of atomic weight, and icy planets), the addition of ammonia to water affects the phase diagram of pure water in unexpected ways. For example at high ammonia concentrations, (>25 wt. %) Ice IV, a metastable phase in the pure water phase diagram is the first phase to crystallize. On further compression Ice IV transforms directly to Ice VII with a staggering 13 % density increase. The equation of state of Ice VI has also been studied, and has an impressively low bulk modulus of only 6 GPa. Pressure, temperature, volume and composition data in conjunction with the associated phase equilibria provide strong constraints for quantum mechanical calculations.
Campbell John A.
Heinz Dion L.
Miller Natalia
Prakapenka Vitali B.
Seagle Christopher T.
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