Si-B alloys are considered as phase change materials (PCMs) in the thermal energy storage (TES) systems due to their high latent heats and moderate temperatures. In order to successful apply them, proper Si-B alloy composition and a suitable ceramic refractory material that can survive long time corrosion at high temperatures should be determined. Here, we investigate serials of Si-B alloys with the B range of 2-11 mass % in graphite crucibles in the temperature range 1450-1750 oC. This work shows that the interaction between Si-B alloys and graphite goes into two stages. Single SiC is formed at the interface at the B content of 2 mass %. SiC and B4C are produced at the interface at the B contents of higher than 5 mass %. Additionally, the results of structural characterization are supported by thermodynamic calculation. These results provide reliable data in the use of Si-B alloys as PCMs in the TES systems.