Iron melting curve with a tricritical point

TL;DR

This paper models the melting curve of iron with a tricritical point using Landau theory, providing a formula that accurately fits experimental data and predicts high-pressure melting temperatures relevant to Earth's core.

Contribution

The study introduces a novel model for melting curves with a tricritical point, deriving explicit pressure dependence formulas validated by experimental data for iron.

Findings

Excellent agreement with high-pressure iron melting data

Derived formulas for entropy change, latent heat, and volume contraction

Predicted Earth's core melting temperatures for iron

Abstract

Solidification as a first order phase transition is described in the Landau theory by the same equation as tricritical phenomena. Here, the solidification or melting temperature against pressure curve is modelled to end at a tricritical point. The model gives the phase transition temperature's dependence on pressure up to the quadratic term with a definite expression for the coefficients. This formula is expected to be generally valid for pure materials having melting curves with dT/dP approaching zero at very high P. Excellent experimental agreement is obtained for iron, the material having the most high pressure data which rather accurately determines the value of the coefficient defining the curvature. The geophysically interesting iron solidification temperatures at the Earth's core pressures are obtained. In addition, the general formulae for entropy change, latent heat and volume contraction in solidification are found and calculated for iron as functions of pressure and temperature.