Study on preparation and thermal properties of new inorganic eutectic binary composite phase change materials

It is important to improve phase change materials (PCMs) with appropriate temperature and excessive latent heat to accelerate the application of latent heat energy storage technology in solar energy storage systems. In this paper, the eutectic salt of NH4Al(SO4)2·12H2O (AASD) and MgSO4·7H2O (MSH) was prepared and the performance was studied. The DSC results show that the optimum content of AASD in the binary eutectic salt is 55 wt%, the melting point was 76.4 °C, and the latent heat is up to 189.4 J g-1, which is suitable for solar power storage systems. Four nucleating agents (KAl(SO4)2·12H2O, MgCl2·6H2O, CaCl2·2H2O, CaF2) and two thickening agents (sodium alginate, soluble starch) are added to the mixture in varying proportions to improve its supercooling. The best combination system was 2.0 wt% KAl(SO4)2·12H2O/1.0 wt% sodium alginate with a supercooling degree of 24.3 °C. After thermal cycling tests, the best formulation of the AASD-MSH eutectic salt phase change material was determined to be 1.0 wt% CaCl2·2H2O/1.0 wt% soluble starch. The latent heat was 176.4 J g-1 and the melting point was 76.3 °C. The supercooling was still lower than 30 °C after 50 thermal cycles, which served as a benchmark for the next investigation.