Development and investigation of form-stable quaternary nitrate salt based composite phase change material with extremely low melting temperature and large temperature range for low-mid thermal energy storage

This paper reports a form-stable molten salt based composite phase change material (CPCM) owning extremely low melting point and large temperature range that can be a promising candidate used in low and middle temperature thermal energy storage fields. The composite was prepared by a so-called cold compress and hot sintering approach with a eutectic quaternary nitrate of Ca(NO3)2-KNO3-NaNO 3-NaNO 2 used as phase change material (PCM), a MgO as structure supporting material (SSM) and graphite as thermal conductivity enhancer (TCE). A series of characterizations were carried out to investigate the composite microstructure, chemical compatibility and thermal properties as well as cycling stability. The results show no chemical reaction occurred among the compositions of salt, SSM and TCEM before and after sintering, indicating excellent chemical and physical compatibility in the composite. A fairly low melting point around 89.56 °C and relatively high decomposition temperature of 628 °C were observed, giving the composite a large energy storage density over 626 kJ/kg at temperature range of 50–600 °C. A mass loading of 50% MgO gives the optimal formulation of the composite at which over 10% graphite can be involved and a thermal conductivity over 1.4 W/m.°C can be obtained. The present results indicate that such a salt based composite with fairly low melting temperature and large temperature range could be an effective alternative to organic based PCMs used in low-mid temperature thermal energy storage.