Preparation and thermal properties of novel inorganic-organic eutectic composite material with high latent heat and thermal conductivity based on aluminum sulfate salt

Potassium aluminum sulfate dodecahydrate (Alum) and ammonium aluminum sulfate dodecahydrate (AAS) are two potential inorganic phase change materials with high transformation enthalpy. To make them more flexible to match temperature requirements of various fields, the melting temperature needs to be manipulated but less effect on latent heat. In this work, two novel eutectic mixtures of Alum-E and AAS-E were obtained by adding erythritol (E) with high latent heat into aluminum sulfate salts. The results denoted that the melting temperatures of the two eutectic mixtures were 72.46 °C and 73.20 °C when containing 35 wt% and 37 wt% erythritol, respectively. It was worth noting that they still possessed high latent heat of 243.4 J/g and 257.4 J/g. Considering the stability of NH4+ at high temperature, Alum-E was chosen to fabricate Alum-E/EG (expanded graphite) composite material with high thermal conductivity via melt-blending method. EG not only increased the thermal conductivity from 0.61 W/(m·K) to 10.95 W/(m·K) as an excellent enhanced heat transfer carrier, but also prevented leakage of Alum-E/EG composite material effectively as a porous adsorption carrier when contained 15 wt% EG. Moreover, the thermal stability tests indicated that Alum-E possessed favorable thermal stability after 250 heat-cooling cycles. Above all, the obtained composite energy storage material is a promising candidate for afterheat recovery and medium and low-temperature energy storage areas else.