Solidification of Salt Hydrate Eutectics Using Multiple Nucleation Agents

Salt hydrates are a class of phase-change materials (PCMs) capable of storing thermal energy at a high volumetric energy density for a low cost (<$10/kWh_th), making them of interest for improving the energy efficiency of buildings and displacing peak load associated with environmental control systems. However, select salt hydrates are susceptible to irreversible degradation associated with phase segregation, and to undercooling—the occurrence of a metastable liquid below the melting point due to a lack of nucleation sites for the crystalline solid. Here, we present a study of phase-specific epitaxial nucleation agents which mitigate undercooling in eutectic nitrate salt hydrate systems. While eutectics can depress melting temperatures into favorable ranges, metastable eutectics experience undercooling. We demonstrate that the nucleation of multiple phases in systems which are susceptible to undercooling can increase the potential for phase segregation and chemical stratification to occur. Furthermore, we illustrate the utility of multiple nucleation agents in these systems to co-crystallize multiple crystalline phases.