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Melting Curve and Phase Relations of Fe-Ni Alloys: Implications for the Earth's Core Composition

Journal Article · · Geophysical Research Letters
DOI:https://doi.org/10.1029/2020gl088169· OSTI ID:1729736
 [1];  [2];  [3];  [1];  [4];  [5];  [1];  [6];  [7];  [8];  [9]
  1. European Synchrotron Radiation Facility (ESRF), Grenoble (France)
  2. European Synchrotron Radiation Facility (ESRF), Grenoble (France); National Centre for Scientific Research (CNRS), Paris (France); Sorbonne Univ., Paris (France)
  3. Univ. degli Studi di Milano (Italy); National Centre for Scientific Research (CNRS), Paris (France); Sorbonne Univ., Paris (France)
  4. Hiroshima Univ. (Japan)
  5. Univ. Kongens, Lyngby (Denmark)
  6. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
  7. Univ. of Rome (Italy)
  8. Ehime Univ., Matsuyama (Japan)
  9. National Centre for Scientific Research (CNRS), Paris (France); Sorbonne Univ., Paris (France)
+ Show Author Affiliations

We discuss that nickel is the second most abundant element in the Earth's core. However, the properties of Fe-Ni alloys are still poorly constrained under planetary cores conditions, in particular concerning the effect of Ni on the melting curve of Fe. Here we show that Ni alloying up to 36 wt% does not affect the melting curve of Fe up to 100 GPa. However, Ni strongly modifies the hexagonal-closed-packed/face-centered-cubic (hcp/fcc) phase boundary, pushing the hcp/fcc/liquid triple point of Fe-20wt%Ni to higher pressures and temperatures. Our results allow constraining the triple point for Fe-10wt%Ni, a composition relevant for the Earth interior, and point out a decrease of the melting temperature at core-mantle boundary by 400 K with respect to pure Fe. A lower amount of light elements than previously predicted is thus required to reduce the crystallization temperature of core materials below that of a peridotitic lower mantle, in better agreement with geochemical observations.

Research Organization:
Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
Sponsoring Organization:
USDOE National Nuclear Security Administration (NNSA)
Grant/Contract Number:
AC52-07NA27344
OSTI ID:
1729736
Report Number(s):
LLNL-JRNL--809365; 1015069
Journal Information:
Geophysical Research Letters, Journal Name: Geophysical Research Letters Journal Issue: 14 Vol. 47; ISSN 0094-8276
Publisher:
American Geophysical UnionCopyright Statement
Country of Publication:
United States
Language:
English

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Related Subjects

36 MATERIALS SCIENCE
58 GEOSCIENCES
Earth composition
FeNi
XAS
hcp/fcc/liquid triple point
melting curve