HR: 1340h
AN: MR23C-0085    [Abstracts]
TI: A new Multi-anvil Assembly for Beamline Experiments up to 15 GPa: Application to in situ Measurement of the Pyroxene-Ilmenite Phase Transition in ZnSiO3
AU: * Mosenfelder, J L
EM: jed@gps.caltech.edu
AF: Geological and Planetary Sciences, Caltech, M/C 170-25, Pasadena, CA 91125 United States
AU: Leinenweber, K
EM: KURTL@asu.edu
AF: Dept of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287-1604 United States
AU: Wang, Y
EM: wang@cars.uchicago.edu
AF: GSECARS, Advanced Photon Source, Argonne, IL 60439 United States
AB: We have developed a new octahedral multi-anvil cell design for use in synchrotron beamline experiments. The design is based on the Bayreuth 14/8 assembly, which employs a stepped-furnace in order to reduce thermal gradients. Two critical alterations have been made to this assembly to decrease X-ray absorption and thereby improve diffraction intensity of the sample: 1) An MgO ``window'' in the zirconia sleeve insulating the graphite furnace has been employed in order to increase X-ray transmission. The MgO window is a simple ring sandwiched between two zirconia cylinders, facilitating assembly compared to other X-ray window designs. 2) Instead of semi-sintered MgO, an injection-molded mullite octahedron is used. This material permits greater X-ray transmission and also has greatly superior thermal insulation compared to MgO. Thus, even with a ``thermally leaky'' MgO window, power consumption is low and the assembly is stable up to 1500°C. The assembly has been tested using the large volume press at sector 13 of the Advanced Photon Source in Chicago. Our first investigation concerned the pyroxene-ilmenite phase transition in ZnSiO₃. This phase transition has the potential to be a useful fixed-point calibration standard for multi-anvil work at 11-12 GPa, a pressure range lying in between other well-calibrated transitions in SiO₂ (Zhang et al. 1996) and Mg₂SiO₄ (Morishima et al. 1994). However, previous data show a discrepancy in location of the ZnSiO₃ boundary of about 0.6 GPa (Akimoto et al. 1977; Ohtani 1979), with poor constraints on the Clapeyron slope. We performed successful reversals of the transition from pyroxene to ilmenite between 900 and 1300°C in a series of four experiments. The sample was contained in a BN capsule and CsCl and W were used as pressure standards. More experiments are needed in order to reverse the transition from ilmenite to pyroxene. We will present results from these initial experiments and discuss the characteristics of the cell and prospects for future studies.
DE: 3620 Mineral and crystal chemistry (1042)
DE: 3630 Experimental mineralogy and petrology
DE: 3924 High-pressure behavior
DE: 3994 Instruments and techniques
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005