Abstract
In recent decades,MgSO4·7H2O(epsomite)has attracted significant attention as a promising thermochemical-based thermal energy storage material due to its high theoretical energy density,wide availability,and affordability.Despite extensive research efforts,progress in achieving high-energy density has been limited,primarily due to inadequate understanding of its reaction mechanisms and unfavorable dehydration/hydration kinetics.This study systematically investigated the hydration/dehydration kinetics and cyclability of MgSO4·7H2O.The results reveal that the dehydration process is influenced by the heating rate,with an optimal rate of 5 ℃/min,resulting in a seven-step MgSO4·7H2O dehydration process with a dehydration heat close to the theoretical value.The reaction kinetic analysis indicated that the rate of hydration was approximately 50％lower than that of dehydration.In addition,thermal cycling tests of MgSO4.7H2O under the conditions of this study(small sample size)indicated good cyclability,with hydration rates increasing with increasing cycling numbers up to approximately 10 cycles where level-off occurs.These results are consistent with scanning electron microscopy analyses,which revealed the formation of cracks and channels in the salt hydrate particles,facilitating mass transfer and improved kinetics.
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