MgSO4 composites in a ferroaluminophosphate for enhancement of volumetric heat storage capacity at a low charging temperature

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Abstract
Ferroaluminophosphate (FAPO4‐5)/MgSO4 composites were prepared as a series of new materials with low charging temperatures and improved volumetric heat storage capacities. A microporous zeolithic compound FAPO4‐5 was used as an adsorbent of water vapor and a matrix of MgSO4 salt particles. Composites with various MgSO4 contents (5‐40 wt%) were then prepared using a wet impregnation method. The MgSO4 salt particles were impregnated into the micropores and textural pores of FAPO4‐5 without the crystal structure of the host material, confirmed by XRD patterns. Although nitrogen adsorption isotherms of the composites showed approximately a half of FAPO4‐5 pore was blocked by MgSO4, the water uptake of the composites reached the sum of those from FAPO4‐5 and MgSO4. The dehydration temperature of MgSO4 in the FAPO4‐5 matrix decreased with its decreasing content due to the easier dehydration of FAPO4‐5. The heat storage recovery of the 25 wt% loaded sample at 80°C was 85.5% while that of MgSO4 was 52.2%. The swelling and agglomeration of the composites containing 25 wt% and less salt were suppressed by the micro and textural pores of FAPO4‐5. The composite at 25 wt% of MgSO4 loading exhibited a total volumetric heat storage capacity of 174 kW h m−3 based on the volume in the hydrated state.

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