MgSO 4 composites in a ferroaluminophosphate for enhancement of volumetric heat storage capacity at a low charging temperature

Summary Ferroaluminophosphate (FAPO 4 ‐5)/MgSO 4 composites were prepared as a series of new materials with low charging temperatures and improved volumetric heat storage capacities. A microporous zeolithic compound FAPO 4 ‐5 was used as an adsorbent of water vapor and a matrix of MgSO 4 salt particles. Composites with various MgSO 4 contents (5‐40 wt%) were then prepared using a wet impregnation method. The MgSO 4 salt particles were impregnated into the micropores and textural pores of FAPO 4 ‐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 FAPO 4 ‐5 pore was blocked by MgSO 4 , the water uptake of the composites reached the sum of those from FAPO 4 ‐5 and MgSO 4 . The dehydration temperature of MgSO 4 in the FAPO 4 ‐5 matrix decreased with its decreasing content due to the easier dehydration of FAPO 4 ‐5. The heat storage recovery of the 25 wt% loaded sample at 80°C was 85.5% while that of MgSO 4 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 FAPO 4 ‐5. The composite at 25 wt% of MgSO 4 loading exhibited a total volumetric heat storage capacity of 174 kW h m −3 based on the volume in the hydrated state.