Interaction of Fe and Fe3C with hydrogen and nitrogen at 6–20 GPa: a study by in situ X-ray diffraction
- 88 Downloads
A method of in situ X-ray diffraction at Spring-8 (Japan) was used to analyze simultaneously the hydrogen incorporation into Fe and Fe3C, as well as to measure the relative stability of carbides, nitrides, sulfides, and hydrides of iron at pressures of 6–20 GPa and temperatures up to 1600 K. The following stability sequence of individual iron compounds was established in the studied pressure and temperature interval: FeS > FeN > FeC > FeH > Fe. A change in the unit-cell volume as compared to the known equations of state was used to estimate the hydrogen contents in carbide Fe3C and hydride FeHx. Data on hydride correspond to stoichiometry with x ≈ 1. Unlike iron sulfides and silicides, the solubility of hydrogen in Fe3C seemed to be negligibly low—within measurement error. Extrapolating obtained data to pressures of the Earth’s core indicates that carbon and hydrogen are mutually incpompatible in the iron–nickel core, while nitrogen easily substitutes carbon and may be an important component of the inner core in the light of the recent models assuming the predominance of iron carbide in its composition.
Keywordsiron carbide hydride nitride high pressure X-ray diffraction experiment
Unable to display preview. Download preview PDF.
- B. Chen, L. Gao, B. Lavina, P. Dera, E. Alp, E. J. Zhao, and J. Li, “Magneto–elastic coupling in compressed Fe7C3 supports carbon in Earth’s inner core,” Geophys. Res. Lett. 39, L18301, (2012). doi: 10.1029/2012gl052875Google Scholar
- J. C. Jamieson, J. N. Fritz, and M. H. Manghnani, “Pressure measurement at high temperature in X–ray diffraction studies: gold as a primary standard,” in High Pressure Research in Geophysics, Ed. by S. Akimoto and M. H. Manghnani (Center for Academic Publications, Tokyo, 1982), pp. 27–48.CrossRefGoogle Scholar
- A. N. Krot, K. Keil, E. R. D. Scott, C. A. Goodrich, and M. K. Weisberg, “Classification of meteorites,” in Treatise on Geochemistry, Ed. by H.D. Holland and K.K. Turekian, (Elsevier–Pergamon, Oxford, 2003), Vol. 1, pp. 83–128.Google Scholar
- K. D. Litasov and A. F. Shatskiy, Composition and Structure of the Earth’s Core (SO RAN, Novosibirsk, 2016b) [in Russian].Google Scholar
- K. D. Litasov, I. S. Sharygin, P. I. Dorogokupets, A. Shatskiy, P. N. Gavryushkin, T. S. Sokolova, E. Ohtani, J. Li, and K. Funakoshi, “Thermal equation of state and thermodynamic properties of iron carbide Fe3C to 31 GPa and 1473 K,” J. Geophys. Res.: Solid Earth 118 (10), 5274–5284 (2013).CrossRefGoogle Scholar
- K. Sakamaki, Takahashi, E. Nakajima, Y. Nishihara, Y. Funakoshi, K. Suzuki, T. and Fukai, Y. “Melting phase relation of FeHx up to 20 GPa: implication for the temperature of the Earth’s core,” Phys. Earth Planet. Inter. 174 (1), 192–201 (2009).Google Scholar
- Y. Shibazaki, E. Ohtani, H. Fukui, T. Sakai, S. Kamada, D. Ishikawa, S. Tsutsui, A. Q. R. Baron, N. Nishitani, N. Hirao, and K. Takemura, “Sound velocity measurements in DHCP–FeH up to 70 GPa with inelastic X-ray scattering: implications for the composition of the Earth’s core,” Earth Planet. Sci. Lett. 313, 79–85 (2012).CrossRefGoogle Scholar
- H. Terasaki, E. Ohtani, T. Sakai, S. Kamada, H. Asanuma, Y. Shibazaki, N. Hirao, N. Sata, Y. Ohishi, and T. Sakamaki, “Stability of Fe–Ni hydride after the reaction between Fe–Ni alloy and hydrous phase (δ–AlOOH) up to 1.2 Mbar: possibility of H contribution to the core density deficit,” Phys. Earth Planet. Inter. 194, 18–24 (2012).CrossRefGoogle Scholar
- S. Urakawa, M. Morishima, T. Kato, A. Suzuki, and O. Shimomura, “Equation of state for h–BN,” Photon Factory Activity Report G275, 383–383 (1993).Google Scholar
- S. Urakawa, K. Someya, H. Terasaki, T. Katsura, S. Yokoshi, K. Funakoshi, W. Utsumi, Y. Katayama, Y. Sueda, and T. Irifune, “Phase relationships and equations of state for FeS at high pressures and temperatures and implications for the internal structure of Mars,” Phys. Earth Planet. Inter. 143, 469–479 (2004).CrossRefGoogle Scholar