A High-Pressure Compound of Argon and Nickel: Noble Gas in the Earth’s Core?

Journal Article · Tue Oct 01 00:00:00 EDT 2019 · ACS Earth and Space Chemistry

DOI:https://doi.org/10.1021/acsearthspacechem.9b00212· OSTI ID:1575040

Adeleke, Adebayo A. ^[1]; Kunz, Martin ^[2]; Greenberg, Eran ^[3]; Prakapenka, Vitali B. ^[3]; Yao, Yansun ^[1]; Stavrou, Elissaios ^[4]

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1. Univ. of Saskatchewan, Saskatoon, SK (Canada)
2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Advanced Light Source
3. Univ. of Chicago, Chicago, IL (United States). Center for Advanced Radiation Sources
4. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Physical and Life Sciences Directorate

Various geophysical models have shown that Ar, a natural decay product of ⁴⁰K, is depleted in Earth’s main reservoirs (i.e., continental crust, atmosphere, and silicate mantle). This indicates that a large amount of Ar may be present in the Earth’s core, but such consideration is hindered by the lack of knowledge on the reactability of Ar with the core’s main constituents (Ni and Fe). Here we demonstrate the synthesis of a thermodynamically stable compound of Ar and Ni under thermodynamic conditions representative of the Earth’s core. Using in situ synchrotron X-ray diffraction and density functional calculations, we identified the compound as ArNi with a L1₁ Laves structure. The ArNi compound is stabilized by notable electron transfer from Ni to Ar, changing their electron configurations toward 3d⁷ and 4s¹. The present results suggest that the abundance of Ar in the Earth’s core is controlled, beyond a simple solubility of Ar in molten Ni–Fe, by chemical bonding, which is truly extraordinary considering the inert nature of Ar under ambient conditions. Furthermore, establishing the Earth’s core as a viable reservoir for Ar helps to postulate the natural decay of ⁴⁰K in the core as a heating source for Earth’s inner dynamics.

• 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: 1575040
• Alternate ID(s): OSTI ID: 1605443
• Report Number(s): LLNL-JRNL--764601; 954325
• Journal Information: ACS Earth and Space Chemistry, Journal Name: ACS Earth and Space Chemistry Journal Issue: 11 Vol. 3; ISSN 2472-3452
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
58 GEOSCIENCES
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
Argon compounds
Density functional theory
Earth core composition
High-pressure chemistry
X-ray diffraction