Growth of the Phase Change Enthalpy Induced by the Crystal Transformation of an Inorganic–Organic Eutectic Mixture of Magnesium Nitrate Hexahydrate–Glutaric Acid

Developing phase change materials (PCMs) with high latent heat is significant for latent heat storage technology. Herein, an inorganic–organic eutectic mixture PCM of Mg­(NO₃)₂·6H₂O (MNH) and glutaric acid (GA) exhibited a melting enthalpy of 189.0 J·g^–1, which is higher than that of each raw material. The characterizations of the structure and crystallization behavior revealed that the increase in latent heat was associated with the crystalline transformation of the MNH–GA eutectic. Additionally, the thermal stability of the MNH–GA eutectic was enhanced because the decreased melting temperature of 66.7 °C was lower than the dehydration temperature. Compared with expanded graphite (EG), expanded perlite (EP) with a larger pore size is a more suitable supporting material for the MNH–GA eutectic because the small layer gaps within EG hinder the phase transformations of the MNH–GA eutectic. The thermal reliability of MNH–GA/EP could have a high stability, and the latent heat only decreased by 2.3 J·g^–1 after 100 thermal cycles.