A latent heat method to detect melting and freezing of metals at megabar pressures

TL;DR

This paper introduces a novel experimental method combining pulsed electrical heating and diamond anvil cells to measure the latent heat of fusion and melting curves of metals at megabar pressures, exemplified by platinum.

Contribution

It presents the first use of this technique to measure the melting curve of platinum at unprecedented high pressures, providing new data for planetary modeling.

Findings

Melting temperature of platinum increases from ~3000 K at 34 GPa to ~4500 K at 107 GPa.

The melting curve is linear with compression, fitting the Kraut-Kennedy model.

The technique enables precise measurement of melting curves at extreme pressures.

Abstract

The high-pressure melting curves of metals provide simple and useful tests for theories of melting, as well as important constraints for the modeling of planetary interiors. Here, we present an experimental technique that reveals the latent heat of fusion of a metal sample compressed inside a diamond anvil cell. The technique combines microsecond-timescale pulsed electrical heating with an internally-heated diamond anvil cell for the first time. Further, we use the technique to measure the melting curve of platinum to the highest pressure measured to date. Melting temperature increases from $\sim 3000$ K at 34 GPa to $\sim 4500$ K at 107 GPa, thermodynamic conditions that are between the steep and shallow experimental melting curves reported previously. The melting curve is a linear function of compression over the 0 to 20% range of compression studied here, allowing a good fit to the Kraut-Kennedy empirical model with fit parameter $C=6.0$.