Iron‐dominant metallic phases are likely the primary hosts for nitrogen in the reduced deep Earth, hence the storage of nitrogen in the lower mantle and the core is governed by the behavior of the Fe‐N‐C system at high temperatures and pressures. In this study, phase transitions and thermoelastic properties of iron carbonitrides were investigated at high pressure‐temperature conditions by diamond anvil cell experiments and first‐principles calculations. Experimental data revealed no phase transition in
Nitrogen is a critical component of the economy, food security, and planetary health. Many of the world's sustainability targets hinge on global nitrogen solutions, which, in turn, contribute lasting benefits for (i) world hunger; (ii) soil, air, and water quality; (iii) climate change mitigation; and (iv) biodiversity conservation. Balancing the projected rise in agricultural nitrogen demands while achieving these 21st century ideals will require policies to coordinate solutions among technologies, consumer choice, and socioeconomic transformation.
more » « less- Award ID(s):
- 1739823
- NSF-PAR ID:
- 10461629
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Earth's Future
- Volume:
- 7
- Issue:
- 8
- ISSN:
- 2328-4277
- Page Range / eLocation ID:
- p. 865-872
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract ε ‐type Fe4(N0.6C0.4) or Fe7(N0.75C0.25)3up to 60 GPa at room temperature. At high temperature, Fe7(N0.75C0.25)3transforms into the Fe3C‐type phase at ∼27 GPa, and then into the Fe7C3‐type phase at ∼45 GPa, which is also corroborated by our theoretical calculations. We found that the phase stability of iron carbonitrides mainly depends on the N/C ratio, and the elastic properties of iron carbonitrides are dominantly affected by the Fe/(N+C) ratio. Iron carbonitrides with diverse structures may be the main host for nitrogen in the deep mantle. Some iron carbonitride inclusions in lower mantle diamonds could be the residue of the primordial mantle or originate from subducted nitrogen‐bearing materials, rather than iron‐enriched phases of the outer core. In addition, our experiments confirmed the existence of Fe7C3‐type Fe7C3‐Fe7N3solid solutions above 40 GPa. Fe7C3‐type Fe7(C, N)3has comparable density and thermoelastic properties to its isostructural endmembers and may be a promising candidate constituent of the Earth's inner core. -
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Abstract Sharp point electrodes generate significant electric field enhancements where electron impact ionization leads to the formation of electron avalanches that are seeded by photoionization. Photoionization of molecular oxygen due to extreme ultraviolet emissions from molecular nitrogen is a fundamental process in the inception of a positive corona in air. In a positive corona system, the avalanche of electrons in the bulk of the discharge volume is initiated by a specific distribution of photoionization far away from the region of maximum electron density near the electrode where these photons are emitted. Here, we present a new approach to finding the inception conditions for a positive corona, which is based on a differential formulation of the photoionization problem. The proposed iterative solution considers the same inception problem that has been solved in the existing literature by using either an integral approach to photoionization or a differential formulation of photoionization and considering the inception problem as a boundary-value eigenvalue problem. The results are validated by comparisons with previous integral formulations and time dynamic plasma fluid solutions in planar and spherical geometries. The results illustrate ideas advanced in Kaptzov (1950
Elektricheskiye Yavleniya v Gazakh i Vacuume p 610) providing a physically transparent connection between an effective secondary electron emission coefficient due to volume photoionization in a positive corona system and the secondary electron emission in conventional Townsend discharge theory. The results also demonstrate the significance of boundary conditions for accurate corona solutions that are based on a differential formulation of photoionization. -
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Rationale Analyses of the isotope ratios of nitrogen (15N/14N) and oxygen (18O/16O) in nitrate (NO3−) with the denitrifier method require relatively high sample volumes at low concentrations (≤1 μM) to afford sufficient analyte for mass spectrometry, resulting in isotopic offsets compared to more concentrated samples of the same isotopic composition.
Methods To uncover the origins of isotopic offsets, we analyzed the N and O isotope ratios of NO3−reference materials spanning concentrations of 0.5–20 μM. We substantiated the incidence of volume‐dependent isotopic offsets, then investigated whether they resulted from (a) incomplete sample recovery during N2O sparging, (b) blanks – bacterial, atmospheric, or in reference material solutions – and (c) oxygen atom exchange with water during the bacterial conversion of NO3−to N2O.
Results Larger sample volumes resulted in modest offsets in δ15N, but substantial offsets in δ18O. N2O recovery from sparging was less complete at higher volumes, resulting in decreases in δ15N and δ18O due to associated isotope fractionation. Blanks increased detectably with volume, whereas oxygen atom exchange with water remained constant within batch analyses, being sensitive to neither sample volume nor salinity. The sizeable offsets in δ18O with volume are only partially explained by the factors considered in our analysis.
Conclusions Our observations argue for bracketing of NO3−samples with reference materials that emulate sample volumes (concentrations) to achieve improved measurement accuracy and foster inter‐comparability.
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