Helium-hydrogen immiscibility at high pressures

TL;DR

This study investigates the behavior of hydrogen-helium mixtures under high pressure, finding no evidence of miscibility or chemical reactions up to 100 GPa, which informs planetary science models.

Contribution

The paper provides experimental data on hydrogen-helium mixtures at high pressures, showing their immiscibility and lack of chemical reactivity, which was previously uncertain.

Findings

No miscibility observed up to 100 GPa

No chemical reactivity detected

No new compounds formed

Abstract

Hydrogen and helium are the most abundant elements in the universe and they constitute the interiors of gas giant planets. Thus, their equations of states, phase, chemical state, and chemical reactivity at extreme conditions are of great interest. Applying Raman spectroscopy, visual observation, and synchrotron X-ray diffraction in diamond anvil cells (DAC), we performed experiments on H2-He 1:1 and D2-He 1:10 compressed gas mixture up to 100 GPa at 300 K. By comparing with the available data on pure bulk materials, we find no sign of miscibility, chemical reactivity, and new compound formation.