Melting curves of Al,Cu,U and Fe metals utilizing the Lindemann-Gilvarry criterion and parameterization of the equations of state

TL;DR

This paper predicts metal melting curves at high pressures using the Lindemann-Gilvarry criterion combined with equations of state, accounting for isochoric conditions in diamond anvil cells and shock wave data, with specific results for iron at Earth's core boundary.

Contribution

It introduces a method to derive consistent bulk moduli and melting curves by integrating the LG criterion with EOS constraints and shock data, improving high-pressure melting predictions.

Findings

Melting curves for Al, Cu, U, and Fe up to ultra-high pressures.

Iron melting temperature at Earth's inner core boundary estimated at 5900±100K.

Incorporation of isochoric conditions and shock data enhances melting curve accuracy.

Abstract

The prediction of the melting curve of metals by extrapolation to high pressures and temperatures based on the Lindemann-Gilvarry criterion (LG) assuming harmonic Debye solid is presented. The LG formulation uses the bulk modulus B and its pressure derivative B' as fit parameters deduced directly from the equation of state, however, the results are not unique and strongly depends on the chosen equation of state (EOS). By introducing a constraint that the bulk moduli parameters B and B' must simultaneously obey the Lindemann-Gilvarry criterion (LG) and the EOS, consistent bulk moduli are derived. The cold pressure Pc and the cold melting curve are obtained by introducing an effective Gr\"uneisen parameter ($\gamma$eff) to the LG approximated equation together with the above constraint. It is claimed that isochoric condition exists in diamond anvil cells (DAC), thus upon raising the temperature and approaching the melt constant volume is maintained. Isochoric condition in the DAC means that the developed thermal pressure (Pth) should be accounted in the LG formulation. Therefor, the actual pressure (Pc+Pth) sensed by the sample confined in the DAC should be inserted to the LG melting formula. This brings along the demand that the shock waves Hugoniot melting data should serve as anchor for deriving the correct melting curves of metals where the Gr\"uneisen parameter $\gamma$ at ambient conditions ($\gamma$ o) is directly determined. The melting curves up to ultra high pressures of Al, Cu, U and Fe metals are presented and discussed. In this manner, special attention is given to $\epsilon$-Fe as isobaric condition in the DAC has been claimed. Utilizing the present approach we obtain the melting temperature of iron in the earth inner core boundary (ICB, 330GPa) is 5900$\pm$100K.