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

Adebayo A. Adeleke; Martin Kunz; Eran Greenberg; Vitali B. Prakapenka; Yansun Yao; Elissaios Stavrou

doi:10.1021/acsearthspacechem.9b00212

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

Adebayo A. Adeleke, Martin Kunz, Eran Greenberg, Vitali B. Prakapenka, Yansun Yao^*, Elissaios Stavrou

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

10 Scopus citations

Abstract

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. Moreover, 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.

Original language	English
Pages (from-to)	2517-2524
Number of pages	8
Journal	ACS Earth and Space Chemistry
Volume	3
Issue number	11
DOIs	https://doi.org/10.1021/acsearthspacechem.9b00212
State	Published - 21 Nov 2019
Externally published	Yes

Keywords

Argon compounds
Density functional theory
Earth core composition
High-pressure chemistry
X-ray diffraction

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10.1021/acsearthspacechem.9b00212

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title = "A High-Pressure Compound of Argon and Nickel: Noble Gas in the Earth's Core?",

abstract = "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. Moreover, 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.",

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author = "Adeleke, {Adebayo A.} and Martin Kunz and Eran Greenberg and Prakapenka, {Vitali B.} and Yansun Yao and Elissaios Stavrou",

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T2 - Noble Gas in the Earth's Core?

AU - Adeleke, Adebayo A.

AU - Kunz, Martin

AU - Greenberg, Eran

AU - Prakapenka, Vitali B.

AU - Yao, Yansun

AU - Stavrou, Elissaios

PY - 2019/11/21

Y1 - 2019/11/21

N2 - 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. Moreover, 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.

AB - 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. Moreover, 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.

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KW - Earth core composition

KW - High-pressure chemistry

KW - X-ray diffraction

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SN - 2472-3452

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

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