HR: 17:15h
AN: MR34A-06    [Abstracts]
TI: In-situ Sound Velocity Measurements on bcc and hcp Phases of Fe
AU: * Li, B
EM: Baosheng.LI@sunysb.edu
AF: SUNY Stony Brook, ESS Building, Stony Brook, 11794 United States
AU: Kung, J
EM: jkung@notes.cc.sunysb.edu
AF: National Cheng-Kung University, Department of Earth Sciences, Tainan, 70101 Taiwan
AU: Liu, W
EM: wliu3@notes.cc.sunysb.edu
AF: SUNY Stony Brook, ESS Building, Stony Brook, 11794 United States
AU: Mao, W
EM: wmao@uchicago.edu
AF: University of Chicago, 5734 S. Ellis Ave, Chicago, 60637 United States
AU: Mao, H
EM: h.mao@gl.ciw.edu
AF: Carnegie Institute of washington , 5251 Broad Branch Rd., NW , Washington DC, 20015 United States
AU: Uchida, T
EM: uchida@cars.uchicago.edu
AF: University of Chicago, 9700 South Cass Avenue GSECARS/APS, Argonne, 60439 United States
AU: Wang, Y
EM: wang@cars.uchicago.edu
AF: University of Chicago, 9700 South Cass Avenue GSECARS/APS, Argonne, 60439 United States
AB: Simultaneous ultrasonic and synchrotron X-ray studies have provided a unique technique for the study of density and P and S wave velocities for the bcc and the unquenchable hcp phases of iron as well as their behavior during the phase transformation. In current experiment, a 2mm-diameter cylinder is used as stating material and measurements are conducted using a MA-8 type high pressure apparatus installed at GSECARS/APS. X-ray diffraction, travel times of acoustic waves inside the sample, and X-ray images of sample (i.e., sample length) are collected simultaneously. Energy dispersive X-ray diffraction data from the sample and the internal pressure standard (NaCl) are recorded using a solid state Ge detector. According to the X-ray diffraction data, the hcp structured iron phase starts to appear at ~13 GPa and continues to grow with increasing pressure. At the peak pressure of ~17 GPa, a scan of the entire sample region showed no sign of remaining bcc phase. With increasing pressure, discontinuities are obvious in both P and S waves in the pressure range of 10-14 GPa with rapid increase in velocities. It appears that there are acoustic precursors prior to the onset of the phase transition detected by X-ray diffraction. On decompression, the phase transition from hcp back to bcc phase occurs at P~10.5 GPa, marked by a slope change in both P and S velocities. Compared to the data along compression, the phase transition shows a hysteresis of about 2 GPa. Details about the P and S wave velocities (hence the elastic bulk and shear moduli) for both the bcc and hcp phases throughout the phase transitions will be reported and the results for hcp phase will compared with those obtained by other techniques.
DE: 3900 MINERAL PHYSICS
DE: 3909 Elasticity and anelasticity
DE: 3924 High-pressure behavior
DE: 3954 X-ray, neutron, and electron spectroscopy and diffraction
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005