Shenghu Mei1, William. B. Durham1, Donald J. Weidner2, Michael T. Vaughan2, Li Li2, Liping Wang2, Jiuhua Chen2, and Yanbin Wang3
1 Lawrence Livermore National Laboratory, Livermore, CA 94550
2 Stony Brook University, Stony Brook, NY 11794
3 University of Chicago, Chicago IL
APS-GSECARS and NSLS-X17B1 MAP
High-pressure deformation study is an essential means to be employed for investigating the rheological behavior of geological materials at their ambient conditions within the earth's interior. However, due to technical difficulties, high-pressure deformation research has long suffered from a lack of quality experimental data, especially at P > 4 GPa. Recently, a novel solid-medium apparatus called the Deformation-DIA (D-DIA) for investigating deformation behavior of materials at P to 15 GPa has been developed and tested satisfactorily. The D-DIA allows experiments to be carried out at a synchrotron x-ray beamline to make precise measurements in-situ. This technology provides accurate measurement of pressure, differential stress, and sample displacement. We report here results from some preliminary experiments in the D-DIA.
Experiments have been conducted on polycrystalline samples of NaCl, MgO, and
olivine. Samples are cold-pressed powder, inserted along with hard alumina pistons
and a standard material of known elastic properties into a graphite resistance
heater within a 6-mm edge length cubic pressure medium made of boron epoxy.
The cell is first squeezed hydrostatically to reach desired pressures and then
deformed in compression at constant pressure. X-ray diffraction of the elastic
standard provides the measurement of pressure and deviatoric stress in the sample.
Deformation is calculated from periodic x-radiographs of the deformation column.
At this point measurement resolution of sample length change and pressure (or
stress) in-situ is <1 mm and ~100 MPa,
respectively. We are optimistic that stress resolution can be improved by an
order of magnitude in the near future. To date we have carried out constant
displacement rate compression tests at rates of ~1 x 10-5 to 4 x
10-4 s-1 over shortening strains of 10—30% at temperatures
of 500—1200°;C and pressures of 5—12 GPa. With the success of
these preliminary experiments, there is promise that the D-DIA will be able
to conduct quantitative deformation experiments at P-T conditions approaching
those of Earth's transition zone.