Liquid-solid phase transition of hydrogen and deuterium in silica aerogel

摘要

Behavior of hydrogen isotopes confined in disordered low-density nanoporous solids remains essentially unknown. Here, we use relaxation calorimetry to study freezing and melting of H_2 and D_2 in an ～85%-porous base-catalyzed silica aerogel. We find that liquid-solid transition temperatures of both isotopes inside the aerogel are depressed. The phase transition takes place over a wide temperature range of ～4K and non-trivially depends on the liquid filling fraction, reflecting the broad pore size distribution in the aerogel. Undercooling is observed for both H_2 and D_2 confined inside the aerogel monolith. Results for H_2 and D_2 are extrapolated to tritium-containing hydrogens with the quantum law of corresponding states.