HR: 14:10h
AN: T22D-03    [PDF]
TI: Ultrahigh pressure deformation of polycrystaline hcp-cobalt
AU: * Merkel, S
EM: smerkel@issp.u-tokyo.ac.jp
AF: ISSP / Univ. of Tokyo, Kashiwanoha 5-1-5, Kashiwa, Chiba, 277-8581 Japan
AU: Antonangeli, D
EM: antonangeli@esrf.fr
AF: ESRF, BP 220, Grenoble, 38043 France
AU: Fiquet, G
EM: Guillaume.Fiquet@lmcp.jussieu.fr
AF: LMCP, Universite Paris VI, Paris, 75005 France
AU: Yagi, T
EM: yagi@issp.u-tokyo.ac.jp
AF: ISSP / Univ. of Tokyo, Kashiwanoha 5-1-5, Kashiwa, Chiba, 277-8581 Japan
AB: During the past few years, a novel set of methods has been developed allowing direct measurements on elasticity and rheology under static ultrahigh pressures using synchrotron x-ray diffraction and the diamond anvil cell. In particular, the analysis on the development of texture and uniaxial stress in a polycrystalline sample under ultrahigh pressure and non-hydrostatic conditions yielded to very interesting results on the microscopic deformation mechanisms and strength of MgO, silicate perovskite or $\epsilon$-Fe [eg. Merkel et al. 2002, Merkel et al. 2003]. However, our understanding of the properties of the $\epsilon$ phase of iron remains poor. There are considerable uncertainties and disagreement on the results of various experiments or first-principles calculations. In particular, the results of the radial diffraction measurement on $\epsilon$-Fe [Mao et al. 1998] have been highly controversial. In order to address this issue, we performed investigations on polycrystalline hcp-cobalt. Its properties such as the bulk modulus and thermal expansion are very close to those of $\epsilon$-Fe and it is readily available under ambient conditions. Thus, it is a well known material and results from the high pressure radial diffraction experiments can be compared with those from well-established techniques. In the present analysis, we performed a new set a measurements between 0 and 20 GPa under ambient temperature conditions at the ESRF synchrotron source using amorphous boron gasket, monochromatic x-ray beam, and imaging plate techniques. From such an experiment, we are able to extract information on non-hydrostatic stress, elasticity, and preferred orientations of the sample in-situ under high pressure and compare them with results obtained previously on $\epsilon$-Fe. Documenting the evolution of stress, elasticity and texture in hcp metals is of great interest for our understanding of the bulk properties and seismic anisotropy of the Earth's inner core. S. Merkel et al., J. Geophys. Res. 107 (2002) doi: 10.129/2001JB000920. \\ S. Merkel et al., Earth Planet. Sci. Lett. 209 (2003) 351. \\ H. Mao et al., Nature 396 (1998), 741
DE: 3902 Creep and deformation
DE: 3909 Elasticity and anelasticity
DE: 3924 High-pressure behavior
DE: 5120 Plasticity, diffusion, and creep
DE: 8162 Rheology--mantle
SC: Tectonophysics [T]
MN: 2003 Fall Meeting