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Iron Phase Diagram at High Pressures and Temperatures

  • S. K. Saxena
  • L. S. Dubrovinsky

Abstract

Diamond-anvil cell (DAC) high-pressure technique with in situ laser heating of a sample permits the determination of iron phase diagram to pressures reaching planetary cores. The DAC technique in combination with in situ x-ray study of iron has revealed the presence of at least one additional state of iron with possibly a double hexagonal closest packed (DHCP) structure given the name β. A review of the available data, indicates that in addition to the previously known triple points, the BCC( body-centered cubic)-HCP (hexagonal closest packed)-FCC (face centered cubic) and the β-BCC-FCC-melt, the following triple-points may exist in the iron phase diagram: the HCP-FCC-β: pressure (P) = 40 (4) GPa at temperature (T) = 1550 (100) K, the β-FCC-melt: P = 60 (10) GPa at T = 2600 (100) K. We define the stability of β-phase between pressures of 37 to 300 GPa at high temperatures. The HCP-β phase boundary has a small negative dP/dT indicating the similarity of physical properties (molar volume, thermal expansi n and bulk modulus) between the two but a higher entropy and enthalpy for the β-phase. The melting curve of iron has been determined quite reliably with the laser heated sample in the DAC to a pressure of about 80 gigapascal (GPa). The pressure range of melting has been extended to as high as 200 GPa but is not supported by shock-wave data and requires further studies for confirmation.

Keywords

Triple Point Laser Heating Outer Core Ultrahigh Pressure Advance Photon Source 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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References

  1. Ahrens, T. J., Holland, K. G. and Chen, G. Q., 1997, in: Shock temperatures and the melting point of iron. CP429, Shock Compression of Condensed Matter, Schmidt, Dandekar and Forbes, eds. The American Inst. Phys.Google Scholar
  2. Andrault, D., Fiquet, G., Kunz, M., Visocekas, F. and Hausermann, D., 1997, The orthorhombic structure of iron: An in-situ high-T/high-P structure solution and refinement. Science 278: 831.ADSCrossRefGoogle Scholar
  3. Anderson, O. L. and Duba, A., 1997, Experimental melting of iron revisited. J. Geophys. Res. 102: 22659.ADSCrossRefGoogle Scholar
  4. Anderson, O. L. and Isaak, D. G., 2000, Simulated melting curves for phases of iron. American Mineral. (in press).Google Scholar
  5. Bass, J. D., Ahrens, T. J., Abelson, J. R. and Hua, T., 1990, Shock temperature measurements: New results for an iron alloy. J. Geophys. Res. 95:21757.ADSCrossRefGoogle Scholar
  6. Boehler, R., 1986, The phase diagram of iron to 430 kbar, Geophys. Res. Lett., 13: 1153.ADSCrossRefGoogle Scholar
  7. Boehler, R., Nicol, M. and Johnson, M. L., 1987, Internally-heated diamond-anvil cell: Phase diagram and P-V-T of iron in High-Pressure Research in Mineral Physics, Geophys.Monogr. Ser., vol. 39, M. H. Manghnani and Y. Syono eds., TERRAPUB, Tokyo/AGU, Washington DC.Google Scholar
  8. Boehler, R., 1993, Temperatures in the Earth’s core from melting-point measurements of iron at high static pressures, Nature, 363:534.ADSCrossRefGoogle Scholar
  9. Boehler, R., von Bargen, N. and Chopelas, A., 1990, Melting, thermal expansion, and phase transition of iron at high pressures, J. Geophys. Res., 95: 21731.ADSCrossRefGoogle Scholar
  10. Brown, J. M. and McQueen, R. G., 1986, Phase transitions, Grüneisen parameters and elasticity for shocked iron between 77 GPa, J. Geophys. Res., 91: 7485.ADSCrossRefGoogle Scholar
  11. Chen, G.Q and Ahrens, T.J. 1995. Equations of state of a, ε and liquid iron and iron’s melting curve -thermodynamic calculations. Geophys. Res. Lett., 22,21–24.ADSCrossRefGoogle Scholar
  12. Chen, G.Q. and Ahrens, T. 1996. High-pressure melting of iron: new experiments and calculations. Phil. Trans. R. Soc. Lond. A, 354: 1251.ADSCrossRefGoogle Scholar
  13. Coates. P. B. (1981) Multi-valent pyrometry. Metrologia. V 17 103–109.ADSCrossRefGoogle Scholar
  14. Dubrovinsky, L. S., Saxena, S. K., Lazor, P., 1997, X-ray study of iron with in-situ heating at ultra high pressures. Geophys.Res. Lett.24:1835.ADSCrossRefGoogle Scholar
  15. Dubrovinsky, L.S., Saxena S. K, Tutti F., Rekhi S. and LeBehan T., 2000, In situ X-ray study of thermal expansion and phase transition of iron at multimegabar pressure. Phys. Rev. Lett (In press).Google Scholar
  16. Dubrovinsky, L. S., Saxena, S. K., Lazor, P., 1998a, High-pressure and high temperature in situ x-ray diffraction study of iron and corundum to 68 GPa using internally heated diamond-anvil cell. Phys. Chem. Mineral. 25:434.ADSCrossRefGoogle Scholar
  17. Dubrovinsky, L. S., Saxena, S. K., Lazor, P., 1998b, Stability of -iron: A new synchrotron x-ray study of heated iron at high pressures. European J. Mineralogy, 10: 43.Google Scholar
  18. Dubrovinsky, L. S., Lazor, P., Saxena, S. K., Haggkvist, P., Weber, H.P., Le Bihan, T. and Hausermann, D.,1999, Study of laser heated iron using third generation synchrotron x-ray radiation facility with imaging plate at high pressures. Phys. Chem. Mineral., 26:539.ADSCrossRefGoogle Scholar
  19. Fernández Guillermot, A. and Gustafson, P., 1985, An assessment of the thermodynamic properties and the (p,T) phase diagram of iron, High Temp.-High Press., 16: 591.Google Scholar
  20. Funamori, N., Yagi, T. and Uchida, T., 1997, High-pressure and high-temperature in situ x-ray diffraction study of iron to above 30 GPa using MA8-type apparatus. Geophys. Res. Lett. 23:953.ADSCrossRefGoogle Scholar
  21. Gallagher, K.G. and Ahrens, T.J., 1994, First measurements of thermal conductivity of griceite and corundrum at ultra high pressures and the melting point of iron (abstract), EOS Trans. Am. Geophys. Un., 15(Suppl.),653.Google Scholar
  22. Jeanloz, R. and Kavner, A., 1996, Melting criteria and imaging spectroradiometry in laser-heated diamond-cell experiments. Phil. Trans. R. Soc. Lond. A, 354:1307Google Scholar
  23. Larson, A.C. and Von Dreele, R.B., 1994, Los Alamos National Laboratory, LAUR, 86–748,Google Scholar
  24. Lazor, P. and Saxena, S.K., 1996 , Discussion comment on melting criteria and imaging spectroradiometry in laser-heated diamond-cell experiments (by R. Jeanloz & A. Kavner), Phil. Trans. R. Soc. Lond. A, 354:1307.Google Scholar
  25. Mao, H.K., Bell, P.M. and Hadidiacos, C., 1987, Experimental phase relations of iron to 360 kbar, 1400°C, determined in an internally heated diamond anvil apparatus, in High-Pressure Research in Mineral Physics, Geophys.Monogr. Ser., vol. 39, M. H. Manghnani and Y. Syono, eds., TERRAPUB, Tokyo/AGU, Washington DC, 1987.Google Scholar
  26. Saxena, S.K., Shen, G., Lazor, P., 1993, Experimental evidence for a new iron phase and implications for Earth’s core, Science, 260, 1312–1314.ADSCrossRefGoogle Scholar
  27. Saxena, S.K., Shen, G. and Lazor, P., 1994, Temperatures in Earth’s core based on melting and phase transformation experiments on iron, Science, 264,405–407.ADSCrossRefGoogle Scholar
  28. Saxena, S.K., Dubrovinsky, L.S., Häggqvist, P., Cerenius, Y., Shen, G. and Mao, H.K., 1995, Synchrotron X-ray study of iron at high pressure and temperature, Science, 269: 1703.ADSCrossRefGoogle Scholar
  29. Saxena, S.K., Dubrovinsky, L.S. and Häggkvist, P., 1996, X-ray evidence for the new phase ß-iron at high temperature and high pressure, Geophys. Res. Lett., 23:2441.ADSCrossRefGoogle Scholar
  30. Shen, G. Mao, H. K., Hemley, R. J., Duffy, T. S., Rivers, M. L., 1998, Melting and crystal structure of iron at high pressures. Geophys. Res. Lett., 25:373.ADSCrossRefGoogle Scholar
  31. Yoo, C. S., Holmes, N.C. and Ross, M., 1993, Shock temperatures and melting of iron at earth core conditions. Phys. Rev. Lett. 70: 3931.ADSCrossRefGoogle Scholar
  32. Yoo, C.S., Akella, J., Campbell, A.J., Mao, H.K. and Hemley, R.J., 1995, Phase diagram of iron by in situ X-ray diffraction: Implications for Earth’s core, Science, 270:1473.ADSCrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media New York 2000

Authors and Affiliations

  • S. K. Saxena
    • 1
  • L. S. Dubrovinsky
    • 2
  1. 1.Center for Study of Matter at Extreme Conditions, VH-150Florida International UniversityMiamiUSA
  2. 2.Institute of Earth SciencesUppsala UniversityUppsalaSweden

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