Title
Understanding the Hydration Process of Salts: The Impact of a Nucleation Barrier
Author
Sogütoglu, L.C.
Steiger, M.
Houben, J.
Biemans, D.
Fischer, H.R.
Donkers, P.A.J.
Huinink, H.
Adan, O.C.G.
Publication year
2019
Abstract
The solid-state hydration of salts has gained particular interest within the frame of thermochemical energy storage. In this work, the water vapor pressure-temperature (p-T) phase diagram of the following thermochemical salts was constructed by combining equilibrium and nonequilibrium hydration experiments: CuCl 2 , K 2 CO 3 , MgCl 2 ·4H 2 O, and LiCl. The hydration of CuCl 2 and K 2 CO 3 involves a metastable zone of ca. 10 K, and the induction times preceding hydration are well-described by classical homogeneous nucleation theory. It is further shown for K 2 CO 3 (metastable) and MgCl 2 ·4H 2 O (not metastable) through solubility calculations that the phase transition is not mediated by bulk dissolution. We conclude that the hydration proceeds as a solid-solid phase transition, mobilized by a wetting layer, where the mobility of the wetting layer increases with increasing vapor pressure. In view of heat storage application, the finding of metastability in thermochemical salts reveals the impact of nucleation and growth processes on the thermochemical performance and demonstrates that practical aspects like the output temperature of a thermochemical salt are defined by its metastable zone width (MZW) rather than its equilibrium phase diagram. Manipulation of the MZW by e.g. prenucleation or heterogeneous nucleation is a potential way to raise the output temperature and power on material level in thermochemical applications. © Copyright 2019 American Chemical Society.
Subject
Copper compounds
Heat storage
Hydration
Hydrostatic pressure
Lithium compounds
Magnesium compounds
Nucleation
Phase diagrams
Potash
Salts
Wetting
Equilibrium phase diagrams
Heterogeneous nucleation
Homogeneous nucleation
Metastable zone width
Nucleation and growth
Solid-solid phase transitions
Solubility calculations
Thermochemical energy storage
Chlorine compounds
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TNO identifier
866585
Publisher
American Chemical Society
ISSN
1528-7483
Source
Crystal Growth and Design, 19 (4), 2279-2288
Document type
article