Hydrogen permeability through a mixed molten salt of LiF, NaF and KF (Flinak) as a heat-transfer fluid

Permeability, diffusivity and solubility of hydrogen in Flinak, a mixed molten salt of LiF (46.5%), NaF (11.5%) and KF (42%), were determined using a vessel supported by a Ni plate. Diffusion-limiting permeation was confirmed by experimental data where hydrogen permeation rates were in reverse proportion to the thickness of Flinak. Diffusivities determined in the range of 500–750 °C were correlated to an Arrhenius equation with the activation energy of 50 kJ/mol. Since the dependence of hydrogen solubility in Flinak on pressure was almost linear, hydrogen was dissolved as H2 in Flinak. The H2 solubility in Flinak was correlated to a Henry law, and its solubility constant was discussed in terms of macroscopic surface tension and unspecified interaction energy between the molten salt and dissolved gaseous molecules.