Preparation and characterization of composite hydrate salt PCM of industrial grade disodium hydrogen phosphate with sodium carbonate

Summary Phase‐change materials (PCMs) can be used to restore abundant heat energy and release thermal energy when it is needed, thus a continuous supply of thermal energy from renewable energy resource such as solar energy is expected to be provided. In this article, industrial grade Na 2 HPO 4 ·12H 2 O is used to prepare composite PCM with Na 2 CO 3 ·10H 2 O so as to improve its performance in phase transition. It is shown that an appropriate composite material that composes of 90% industrial grade Na 2 HPO 4 ·12H 2 O and 10% analytical pure Na 2 CO 3 ·10H 2 O is with the lowest degree of supercooling (6.0°C), the longest exothermic plateau duration (10.6 minutes), and the melting solution is clear without phase separation. Furthermore, by adding 2.25% Na 2 SiO 3 ·9H 2 O to above composite PCM, a more promised composite material is obtained, which is with the crystallization temperature of 28.4°C, the lower supercooling degree of 2.5°C, and heat release plateau of 10.2 minutes during cooling, it has a good cyclic stability of heating‐cooling.