Composite hydrate salt Na₂HPO₄·12H₂O–Na₂SO₄·10H₂O and its thermal storage properties

Phase change thermal storage materials store and release thermal energy through changes in their physical state at the phase transition temperature, which is widely used in thermal utilization applications. The main problems with inorganic phase change thermal storage materials are phase separation and supercooling phenomena. In this paper, the preparation of composite phase change material (disodium hydrogen phosphate dodecahydrate (Na₂HPO₄·12H₂O)–sodium sulfate decahydrate (Na₂SO₄·10H₂O)) is conducted by using the co-melting method so as to reduce the phase separation and supercooling. The evaluation of the thermal storage properties of this composite material is performed as well. The results show that the phase separation phenomenon is eliminated in the composite material with a mass ratio of 9:1 for disodium hydrogen phosphate dodecahydrate:sodium sulfate decahydrate, which has the highest crystallizing temperature of 28·2°C, excellent heat storage performance and lowest supercooling degree of about 4·8°C. The heating–cooling cyclic tests indicate that the composite material is stable up to 200 heating–cooling cycles. The X-ray diffraction result shows that the composite material consists of the components disodium hydrogen phosphate dodecahydrate and sodium sulfate decahydrate only.