Thermal cycling testing of Zn–Mg–Al eutectic metal alloys as potential high-temperature phase change materials for latent heat storage

This article presents the thermal stability testing results of five high-temperature phase change materials for their potential use in latent thermal energy storage systems. The tested materials are eutectic metal alloys [Zn84Al8.7Mg7.3, Zn88.7Al11.3, Zn92.2Mg7.8, Zn72Mg28 and Mg70Zn24.9Al5.1 (at.%)] with phase change temperatures in the range of 340–380 °C. The five candidates have been selected not only for their adequate melting temperature and high fusion enthalpy, but also for the availability and appropriate costs [2–3 $/kg (Rodríguez-Aseguinolaza in J Therm Anal Calorim 117:93–99, 2014)] of Zn, Al, and Mg primary metals. As it is well known and demonstrated in previous works, the use of metal alloys presents noticeable benefits on the TES solutions based on their implementation. The particular advantages introduced by the Zn–Mg–Al system in terms of maximization of the storage capacity and appropriate operation temperature justify a deeper analysis of these alloys, previously studied, for a complete thermal performance. In this work, with the aim of reproducing a realistic thermal cycling behaviour in real heat storage applications, the selected candidates have been subjected to short- and long-term thermal cycling tests by 100 and 500 melting/solidification cycles, respectively. These experiments permitted to detect any potential evolution of the thermodynamic and structural properties of the investigated materials that could be sign of an undesirable chemical decomposition or phase segregation. As a conclusion, the Zn84Al8.7Mg7.3, Zn88.7Al11.3, Mg72Zn28 and Mg70Zn24.9Al5.1 alloys have been identified as very promising latent heat storage materials due to their long-term thermal stability.