A Pilot Study of PVT Equations of State of Fluids In a Diamond Anvil Cell

Quanzhong Guo1, Ho-kwang Mao1, Jingzhu Hu1, Russell J. Hemley1, Guoyin Shen2

1Geophysical Laboratory, Carnegie Institution of Washington, Washington DC, USA.

2Consortium for Advanced Radiation Sources, The University of Chicago, Chicago, IL, USA.

qguo@bnl.gov

APS-GSECARS

Unlike the densities of crystalline solids, which can be obtained by x-ray diffraction of very small samples in the diamond anvil cell at multimegabar pressures, density measurements of fluids and amorphous materials are limited to relatively low pressures and temperatures. Information on the densities and specific volumes of fluids, melts, and amorphous solids at high pressures and temperatures is a key to understanding many geochemical and cosmochemical processes. Indirect methods for the volume measurement of amorphous materials, such as Brillouin scattering spectroscopy [1], yield high-pressure densities only for purely elastic systems. If the system goes through a structural change [2], liquid-liquid phase transition [3], or dissolution-precipitation reaction, processes that often occur at high pressure [4], these methods are not applicable. The GSECARS bending magnet beamline and the x-ray micro-radiographic technique developed there are ideal for the measurement of sample volumes in diamond anvil cells. Because the sample between two parallel diamond anvil surfaces can be closely approximated as two-dimensional, and the sample thickness determined by the radiography measurement, the volume of the sample can be determined without rotating the sample. Our preliminary results from pressure-volume-temperature measurements on water demonstrate the feasibility of the micro-radiographic technique for density determinations of amorphous materials in the diamond anvil cell.

References

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