Oral: Theoretical Model for the Thermodynamics of Iron at High Pressures near Melting
ORAL
Abstract
The Fe pressure-temperature phase diagram and its melting line have various applications, such as providing constraints to iron-core planetary models.
We propose an equation of states (EOS) model based on the interstitials theory of simple condensed matter (ITCM) suggested by A.V. Granato [1], which, when applied to Fe, allows extrapolation of measured phase lines to Earth’s inner core boundary (ICB) conditions. The ITCM describes the solid-liquid phase transition in metals as resulting from a high concentration of interstitials-like defects, resulting from strong nonlinearity of their self-interaction.
The original model is expanded to describe melting over a wide range of pressures and temperatures rather than focusing on a specific isobaric transition.
The model is then used to fit the measured melting data and extrapolate it to cover ICB conditions, and used to create a multiphase EOS covering this regime.
The model is used to explain contradictory data regarding the location of the melting line as a result of a novel phase transition between two separate liquid phases, specifically between the FCC-based and the HCP-based liquids. Thus, it also offers a new interpretation for the previously suggested near-melting high-pressure phase [2]. Similarly, this additional transition may offer a new solution to the inner core nucleation paradox [3].
1. A. V. Granato, Phys. Rev. Lett 68, 974 (1992).
2. R. Boehler, Geophys. Res. Lett 13, 1153 (1986).
3. L. Huguet, Earth Planet. Sci. Lett 487, 9 (2018).
We propose an equation of states (EOS) model based on the interstitials theory of simple condensed matter (ITCM) suggested by A.V. Granato [1], which, when applied to Fe, allows extrapolation of measured phase lines to Earth’s inner core boundary (ICB) conditions. The ITCM describes the solid-liquid phase transition in metals as resulting from a high concentration of interstitials-like defects, resulting from strong nonlinearity of their self-interaction.
The original model is expanded to describe melting over a wide range of pressures and temperatures rather than focusing on a specific isobaric transition.
The model is then used to fit the measured melting data and extrapolate it to cover ICB conditions, and used to create a multiphase EOS covering this regime.
The model is used to explain contradictory data regarding the location of the melting line as a result of a novel phase transition between two separate liquid phases, specifically between the FCC-based and the HCP-based liquids. Thus, it also offers a new interpretation for the previously suggested near-melting high-pressure phase [2]. Similarly, this additional transition may offer a new solution to the inner core nucleation paradox [3].
1. A. V. Granato, Phys. Rev. Lett 68, 974 (1992).
2. R. Boehler, Geophys. Res. Lett 13, 1153 (1986).
3. L. Huguet, Earth Planet. Sci. Lett 487, 9 (2018).
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Publication: manuscript in preparation
Presenters
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Rann Shikler
The Hebrew University of Jerusalem
Authors
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Rann Shikler
The Hebrew University of Jerusalem
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Yinon Ashkenazy
Racah Institute of Physics, Hebrew University of Jerusalem