Macro-porous permeability aspects of MgSO4 salt hydrate foams for energy storage applications

In the present work a macroporous silicone foam, able to contain the magnesium sulfate, was chosen as matrix for the reversible hydration/dehydration process of the salt hydrate. The aim of the article was addressed towards the assessment of the relationship among microstructure, permeability and mass diffusion of the composite foam. This aspect represents an essential step for the future industrial development of this composite material. The results show that the filler content influences the foam morphology where a transition from closed to mixed and then closed cell again was observed with increasing filler content. Consequently, depending on the distribution and interconnection of the structural channels, a different effectiveness in guaranteeing mass diffusion phenomena was identified. In particular, permeability tests show that foams with 50 wt% of salt hydrates have a highly interconnected microstructure allowing a permeability over three times higher than a closed cell structure making it suitable for thermochemical energy storage applications.