Ultra-high temperature performance of h-BN based composite in contact with molten silicon

Silicon has been recently proposed as a very promising phase change material for applications in latent heat thermal energy storage (LHTES) and conversion systems working at ultra-high temperatures. However, in order to successfully develop such kind of devices, suitable refractories showing low reactivity and non-wetting behavior upon the melting and storing of molten silicon at temperatures much higher than its melting point have to be selected. In our previous work, we have documented that the non-wetting behavior in Si/h-BN system is preserved at temperatures up to 1650 C, with the absence of new reaction products formed at the interface. These findings make hexagonal boron nitride (h-BN) a reasonable first candidate for Si-based LHTES applications. Nevertheless, the rather poor mechanical strength of ''pure'' h-BN ought to be improved in order to enhance the reliability under thermocycling operational conditions and to increase the life period of the device. Therefore, in the present paper, we examine for the first time the interactions at ultra-high temperatures between a high strength commercial h-BN-based composite and molten Si. At temperatures up to 1750 C, the wettability of the h-BN-based composite (h-BN+SiC+ZrO2) with molten Si is much lower if compared to the pure h-BN counterpart. Additionally, the role of reinforcements (SiC+ZrO2) and occured microstructural evolution is discussed based on the results obtained by SEM and XRD analyses.