Ultralow Melting of Iron Nitrides and the Fe–N–C System at High Pressure

Lv, Chaojia; Liu, Jin

doi:10.1029/2021jb023718

Cited by 3 publications

(1 citation statement)

References 83 publications

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“…These results indicate that in the Fe 0 ‐saturated mantle, N released from the slab preferentially partitions into the metallic Fe phase over the silicates. Despite the metallic Fe was proposed to be a potential host for subducted N in the deep mantle (Huang, Wu, et al., 2021; Lv & Liu, 2022), it remains unclear how N is transported from subducted slabs to the metallic Fe of the reduced mantle. It is also unknown whether the volatile‐rich metallic Fe is still capable of concentrating N from slabs.…”

Section: Introductionmentioning

confidence: 99%

Experimental Constraints on the Fate of Subducted Sedimentary Nitrogen in the Reduced Mantle

Huang

Chariton

et al. 2022

JGR Solid Earth

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Nitrogen is considered to be transported from Earth′s surface to the top of the lower mantle through subduction. However, little is known on the transportation and fate of subducted nitrogen to the Earth′s interior during slab‐mantle interactions. In this study, the stability of subducted sedimentary nitrogen in the reduced mantle was investigated to 35 GPa and 1600 K by laser‐heated diamond anvil cell experiments and first‐principles calculations. Our results showed that subducted nitrogen‐bearing silicates and fluids could not coexist with the metallic iron or iron‐rich alloys, and reacted with them to form different products at high pressure‐temperature conditions. Combining our results with previous data, we re‐determined the relative stability of iron‐light element binary compounds to 35 GPa and 1600 K to be Fe‐O > Fe‐N > Fe‐S > Fe‐C. This stability sequence contributes to explaining the observation that iron nitrides are trapped as inclusions in sulfur‐depleted lower‐mantle diamonds and are absent in sulfur‐rich ones. The recycling efficiency of subducted sedimentary nitrogen is strongly related to the availability of the metallic iron of the reduced mantle. Hydration of the metallic iron limits the storage of nitrogen in it and contributes to recycling nitrogen to Earth′s surface. Therefore, unlike subducted continental sediments, subducted marine sediments are unlikely to transport a large amount of surficial nitrogen to the metallic iron of the reduced mantle in which nitrogen could reside over long geologic periods.

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Section: Introductionmentioning

confidence: 99%

Experimental Constraints on the Fate of Subducted Sedimentary Nitrogen in the Reduced Mantle

Huang

Chariton

et al. 2022

JGR Solid Earth

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Lower shear velocity of HCP-Fe under anisotropic stress from first-principles calculations

Jiang

Liu

et al. 2023

Mod. Phys. Lett. B

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Earth’s core consists of a solid inner core and a liquid outer core, composed primarily of iron. The pressure in the solid inner core is about 330 gigapascals (GPa) at the temperature close to the melting point. Considering the extensive experimental and theoretical data, the shear wave ([Formula: see text]-wave) velocity of the inner core is much lower than that of pure iron. Since the lower [Formula: see text]-wave velocity has been observed in the seismic models, reasons have been widely discussed such as the premelting of iron in the Earth’s inner core. In this paper, a new explanation is expected to be proposed under the anisotropic stress. The calculated longitudinal wave and [Formula: see text]-wave velocity of pure hexagonal close-packed iron (HCP-Fe) model based on the density functional theory (DFT) at the different density are matching with the seismic wave, the atomic distribution of HCP-Fe is obtained under the anisotropic stress. Unfortunately, it is unlikely conformed there was an inner-core condition due to the unreal anisotropic stress, although the lower [Formula: see text]-wave velocity is. Somehow, this lower [Formula: see text]-wave velocity may provide a new horizon to build mineralogical models for discussing. In addition, the [Formula: see text]-wave and viscosity of iron are strongly dependent on shear stress, we then give a mathematical equation between the [Formula: see text]-wave velocity and viscosity empirically by the shear behavior. It is revealed that the shear stress of iron has a positive influence on the [Formula: see text]-wave and viscosity.

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Electrical Resistivity and Phase Evolution of Fe–N Binary System at High Pressure and High Temperature

Wang,

Yang,

Shen

et al. 2024

Minerals

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Partitioning experiments and the chemistry of iron meteorites indicate that the light element nitrogen could be sequestered into the metallic core of rocky planets during core–mantle differentiation. The thermal conductivity and the mineralogy of the Fe–N system under core conditions could therefore influence the planetary cooling, core crystallization, and evolution of the intrinsic magnetic field of rocky planets. Limited experiments have been conducted to study the thermal properties and phase relations of Fe–N components under planetary core conditions, such as those found in the Moon, Mercury, and Ganymede. In this study, we report results from high-pressure experiments involving electrical resistivity measurements of Fe–N phases at a pressure of 5 GPa and temperatures up to 1400 K. Four Fe–N compositions, including Fe–10%N, Fe–6.4%N, Fe–2%N, and Fe–1%N (by weight percent), were prepared and subjected to recovery experiments at 5 GPa and 1273 K. These experiments show that Fe–10%N and Fe–6.4%N form a single hexagonal close-packed phase (ɛ-nitrides), while Fe–2%N and Fe–1%N exhibit a face-centered cubic structure (γ-Fe). In separate experiments, the resistivity data were collected during the cooling after compressing the starting materials to 5 GPa and heating to ~1400 K. The resistivity of all compositions, similar to the pure γ-Fe, exhibits weak temperature dependence. We found that N has a strong effect on the resistivity of metallic Fe under rocky planetary core conditions compared to other potential light elements such as Si. The temperature-dependence of the resistivity also revealed high-pressure phase transition points in the Fe–N system. A congruent reaction, ε ⇌ γ’, occurs at ~673 K in Fe–6.4%N, which is ~280 K lower than that at ambient pressure. Furthermore, the resistivity data provided constraints on the high-pressure phase boundary of the polymorphic transition, γ ⇌ α, and an eutectoid equilibrium of γ’ ⇌ α + ε. The data, along with the recently reported phase equilibrium experiments at high pressures, enable construction of a phase diagram of the Fe–N binary system at 5 GPa.

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Ultralow Melting of Iron Nitrides and the Fe–N–C System at High Pressure

Cited by 3 publications

References 83 publications

Experimental Constraints on the Fate of Subducted Sedimentary Nitrogen in the Reduced Mantle

Experimental Constraints on the Fate of Subducted Sedimentary Nitrogen in the Reduced Mantle

Lower shear velocity of HCP-Fe under anisotropic stress from first-principles calculations

Electrical Resistivity and Phase Evolution of Fe–N Binary System at High Pressure and High Temperature

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