Separation of residual salt using vacuum sublimation for molten salt applications

Solid products processed in molten salts often retain residual salt that needs to be removed. Complete removal of the adhered salts without affecting the underlying solid remains challenging because dissolved species may react with the substrate. Conventional vacuum distillation removes residual salts by evaporation but requires remelting of the salt at high temperatures typically above 1000 °C, which may promote undesirable salt-solid reactions and leave non-volatile residues. Herein, we report a vacuum sublimation-based method for residual salt removal at moderate temperatures, thereby avoiding the liquid salt phase and potentially minimizing detrimental salt-solid reactions. In this method, residual LiCl-KCl with dissolved rare earth chlorides is first displaced by rinsing in molten CsCl, followed by vacuum sublimation of the adhered CsCl at 610 °C under 1.33–4.67 Pa, below its melting point. The method was successfully demonstrated on both dense tungsten and porous reticulated vitreous carbon substrates. SEM-EDS analyses confirmed effective removal of residual chloride salts from both external surfaces and internal pore regions, demonstrating the feasibility of vacuum sublimation as a post-processing strategy for cleaning products fabricated in molten salt systems.