Equations of state and anisotropy of Fe-Ni-Si alloys
Abstract
We present powder X‐ray diffraction data on body centered cubic (bcc)‐ and hexagonal close packed (hcp)‐structured Fe_(0.91)Ni_(0.09) and Fe_(0.8)Ni_(0.1)Si_(0.1) at 300 K up to 167 and 175 GPa, respectively. The alloys were loaded with tungsten powder as a pressure calibrant and helium as a pressure transmitting medium into diamond anvil cells, and their equations of state and axial ratios were measured with high statistical quality. These equations of state are combined with thermal parameters from previous reports to improve the extrapolation of the density, adiabatic bulk modulus, and bulk sound speed to the pressures and temperatures of Earth's inner core. We propagate uncertainties and place constraints on the composition of Earth's inner core by combining these results with available data on light‐element alloys of iron and seismic observations. For example, the addition of 4.3 to 5.3 wt% silicon to Fe_(0.95)Ni_(0.05) alone can explain geophysical observations of the inner core boundary, as can up to 7.5 wt% sulfur with negligible amounts of silicon and oxygen. Our findings favor an inner core with less than ∼2 wt% oxygen and less than 1 wt% carbon, although uncertainties in electronic and anharmonic contributions to the equations of state may shift these values. The compositional space widens toward the center of the Earth, considering inner core seismic gradients. We demonstrate that hcp‐Fe_(0.91)Ni_(0.09) and hcp‐Fe_(0.8)Ni_(0.1)Si_(0.1) have measurably greater c/aaxial ratios than those of hcp‐Fe over the measured pressure range. We further investigate the relationship between the axial ratios, their pressure derivatives, and elastic anisotropy of hcp‐structured materials.
Additional Information
© 2018 American Geophysical Union. Received 11 DEC 2017; Accepted 6 APR 2018; Accepted article online 30 APR 2018; Published online 2 JUN 2018. We thank N. V. Solomatova and G. J. Finkelstein for help during the experiments and C. A. Murphy and L. Mauger for help in synthesizing the samples. We are thankful to J. Attanayake for helpful discussions and two anonymous reviewers for their helpful comments. We thank the National Science Foundation (NSF‐EAR‐1727020 and 1316362), the W. M. Keck Institute for Space Studies, and the U.S. Department of Defense (NDSEG) for support of this work. Portions of this work were performed at GeoSoilEnviroCARS Sector 13 (NSF‐EAR‐1634415 and DOE‐GeoSciences DE‐FG02‐94ER14466) at the Advanced Photon Source (a U.S. DOE Office of Science User Facility operated by Argonne National Laboratory DE‐AC02‐06CH11357), and beamline 12.2.2 (supported in part by COMPRES under NSF Cooperative Agreement EAR 10‐43050) at the Advanced Light Source of Lawrence Berkeley National Laboratory (supported by the U.S. DOE, Office of Science DE‐AC02‐05CH11231). Microprobe analyses were carried out at the Caltech GPS Division Analytical Facility (funded in part by the MRSEC Program of the NSF under DMR‐0080065). The data used are listed in the tables, supporting information, and references.Attached Files
Published - Morrison_et_al-2018-Journal_of_Geophysical_Research__Solid_Earth.pdf
Supplemental Material - downloadSupplement_doi=10.1029_2F2017JB015343_attachmentId=2208615350
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Additional details
- Eprint ID
- 86130
- Resolver ID
- CaltechAUTHORS:20180430-141317857
- EAR-1727020
- NSF
- EAR-1316362
- NSF
- Keck Institute for Space Studies (KISS)
- National Defense Science and Engineering Graduate (NDSEG) Fellowship
- EAR-1634415
- NSF
- DE-FG02-94ER14466
- Department of Energy (DOE)
- DE-AC02-06CH11357
- Department of Energy (DOE)
- EAR 10-43050
- NSF
- DE-AC02-05CH11231
- Department of Energy (DOE)
- DMR-0080065
- NSF
- Created
-
2018-04-30Created from EPrint's datestamp field
- Updated
-
2021-11-15Created from EPrint's last_modified field
- Caltech groups
- Keck Institute for Space Studies, Seismological Laboratory, Division of Geological and Planetary Sciences