Compounding MgCl₂·6H₂O with NH₄Al(SO₄)₂·12H₂O or KAl(SO₄)₂·12H₂O to Obtain Binary Hydrated Salts as High-Performance Phase Change Materials.

Developing phase change materials (PCMs) with suitable phase change temperatures and high latent heat is of great significance for accelerating the development of latent heat storage technology to be applied in solar water heating (SWH) systems. The phase change performances of two mixtures, NH₄Al(SO₄)₂·12H₂O-MgCl₂·6H₂O (mixture-A) and KAl(SO₄)₂·12H₂O-MgCl₂·6H₂O (mixture-B), were investigated in this paper. Based on the DSC results, the optimum contents of MgCl₂·6H₂O in mixture-A and mixture-B were determined to be 30 wt%. It is found that the melting points of mixture-A (30 wt% MgCl₂·6H₂O) and mixture-B (30 wt% MgCl₂·6H₂O) are 64.15 °C and 60.15 °C, respectively, which are suitable for SWH systems. Moreover, two mixtures have high latent heat of up to 192.1 kJ/kg and 198.1 kJ/kg as well as exhibit little supercooling. After 200 cycles heating-cooling experiments, the deviations in melting point and melting enthalpy of mixture-A are only 1.51% and 1.20%, respectively. Furthermore, the XRD patterns before and after the cycling experiments show that mixture-A possesses good structure stability. These excellent thermal characteristics make mixture-A show great potential for SWH systems.