Theoretical Equations of State of Iron at the Earth’s Core Conditions
The thermodynamic properties of the Earth’s interior are conveniently studied because of a procedure in common use in mineral physics, i.e. the so-called equation of state. An equation of state, in its canonical formulation, is a relationship between pressure, volume, and temperature. Recent improvements in both the techniques of collecting and inverting seismic data give the possibility of determining remarkably accurate relationships of pressure vs. density for the interior of the Earth . However, to date no information can be extracted about the temperature profile of the Earth; as a matter of fact, the only information we have for the temperature is given by a simple interpolation between the surface values and the semi-quantitative and somehow objectionable values for the outer core. The latter figures are generally determined by a number of assumptions: mainly a semi-empirical melting law, the fact that it is possible to extrapolate the low-pressure data, and the assumption of a pure iron core. In this paper, we approach the problem of the equation of state for the core in the framework of the assumption that it is composed of pure iron; this assumption is dictated by two main reasons. First, we are not completely convinced that a lighter element is needed to fit the proposed shock wave data, since these are not perfectly reliable [2,3]. Second, we feel that in the present state of the research there is no need of further refinements since we are not yet able to properly treat the case of pure iron.
KeywordsPure Iron Helmholtz Free Energy Outer Core Electronic Specific Heat Sublimation Energy
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