Miscibility gap alloys with a ceramic matrix for thermal energy storage

Abstract

New miscibility gap alloys with a ceramic matrix have been explored in the ZrO2–Al, AlN–Al, AlN-(Al–Si), Al2O3–Al and MgO–Al systems with a view to creating oxidation-resistant macroscopically solid, phase change-enhanced, thermal energy storage materials. Materials were manufactured by mixing the components, pressing and firing at 700 °C under argon. Oxidation tests at 700 °C in air for up to 72 h showed a mix of responses. Despite favourable thermodynamic properties of some published Ellingham diagrams, samples in the ZrO2–Al system underwent a strong exchange reaction, which did not result in a useful material. In the AlN–Al, AlN–(Al–Si) systems, viable MGA-type materials with encapsulated Al particles providing latent heat storage within a solid matrix were formed. There was no degradation of the materials after 24 h of oxidation testing; however, severe oxidation of the Al or Al–Si was observed after 72 h. The Al2O3–Al and MgO–Al systems not only formed a viable ceramic matrix material after firing, but also showed no signs of Al oxidation after 72 h in air at 700 °C. These results open up a promising new series of thermal energy storage materials, some of which appear to have very good oxidation resistance under the test conditions.