WEB The Hydration/Metastable Zone of salt hydrated in different silica gelsWednesday (23.09.2020) 15:55 - 16:10 P: Processing and Synthesis 1 Part of:
The solid-state hydration of salts has gained particular interest within the frame of thermochemical energy storage (TCES). However, some salt hydrates have a metastable zone (MSZ) around their equilibrium line between hydrate and anhydrate , where slow kinetics inhibit a fast transition. This limits the available power output of a TCES device.
One solution of this problem may be the confinement of these salt hydrates in porous particles like silica gels. In this work, the water vapour pressure−temperature (p−T) phase diagram of the CuCl2 inside different silica gels was constructed by combining equilibrium and non-equilibrium hydration experiments. The hydration of CuCl2 in silica gels involves a MSZ with a width of ca. 20 K, these boundaries are deviating slightly from the metastable zone found for pure CuCl2. Additionally, the pore size of the silica influences the hydration of the salt and therefore the maximal amount of absorbed water increases with decreasing pore size. We conclude, that the relative humidity (RH) inside the pores differs from the outside RH according to the law of Kelvin over capillary condensation . This leads to easier deliquescence inside the silica gels with small pores compared to the silica gels with large pores or locations outside a silica gel. This could facilitate the integration of salt hydrate in thermochemical energy storage applications and as such improve the power output of these types of energy storages.
This research received funding from the Dutch Organization for Scientific Research (NWO) in the framework of the Materials for sustainability.