Fe-26.38Si-9.35B eutectic alloy is proposed as a phase change material (PCM) as it exhibits high latent heat, high thermal conductivity, moderate melting point, and low cost. For successful implementation of it in the latent heat thermal energy storage (LHTES) systems, we investigate the use of graphite as a refractory material that withstands long-term melting/solidification in contact with the Fe-26.38Si-9.35B alloy. The PCM has been thermally cycled up to 1–4 times below and above its melting point at the temperature interval of 20 °C or 100 °C. It is observed that this eutectic alloy shows good thermal stability over a small temperature range of 1057–1257 °C. Some SiC and B₄C solid precipitation will be formed at the top of the alloy. However, it does not seem to increase with time. The graphite crucible as a refractory material will produce a protective layer of SiC and B₄C that will hinder the interaction between the PCM and the crucible. The small volume change during solidification will not break the graphite crucible during cycling. The chemical wear or dissolution of the crucible is negligible. It demonstrates the viability of Fe-26.38Si-9.35B alloy as a heat storage material in this type of container.

Fe-26Si-9B alloy was selected as a potential phase change material (PCM) to store energy at temperatures up to 1300 °C. A suitable refractory material is crucial to building a PCM container for Fe-26Si-9B alloy in thermal energy storage systems. The refractory material should have the ability to withstand corrosion from liquid Fe-26Si-9B alloy and should not pollute the alloy after long-term thermal cycles at high temperatures. In this work, Si₃N₄ was selected as a candidate refractory material. To investigate the interaction between Si₃N₄ and Fe-26Si-9B alloy, the wettability property of an Fe-26Si-9B/Si₃N₄ system was examined in a sessile drop furnace at temperatures up to 1350 °C. Moreover, Fe-26Si-9B alloy was subjected to 1–12 thermal cycles at temperatures between 1100 and 1300 °C, where the alloys were placed in Si₃N₄ crucibles in a resistance furnace under argon. According to the experiments, the equilibrium contact angle between the Fe-26Si-9B droplet and Si₃N₄ substrate was measured to be ~143°, which is non-wetting behavior. Microstructural analyses showed that FeSi, FeB, FeSiB₃, and SiB₆ were formed in the solidified Fe-26Si-9B alloy, in which FeSi + FeSiB₃ constituted the eutectic structure. No nitride phases were introduced to the Fe-26Si-9B alloy, and no new interlayer was produced at the interface between the Fe-26Si-9B alloy and Si₃N₄ crucible after the thermal cycle experiments. In addition, the formed phases were stable with the increase in thermal cycles. All the results show that Si₃N₄ refractory material is suitable for Fe-26Si-9B alloy containers at high temperatures.

Si-B alloys are proposed as a potential phase change material (PCM) in the novel high temperature thermal energy storage systems. For successfully introducing the new PCM, the selection of proper refractory material in the PCM container is vital. At present, graphite is chosen as a potential refractory material for the PCM container, due to its high temperature stability, low thermal expansion, and high thermal conductivity. The Si-B alloys and the high-temperature interaction with graphite are hence studied. The phase formation in the Si-B alloys and the interaction with graphite at B content of 2–11 mass % and temperatures of 1450–1750 °C were investigated. Carbides were observed at the interface between the solidified alloys and the graphite. A single SiC layer was produced at B content of 2 and 3.25 mass %. Otherwise, SiC and B₄C layers were generated at B content higher than 5 mass %. In the Si-B-C system, the phase formation is dependent on the B content. Moreover, the equilibrium B content is calculated to be 3.66 mass % in the molten Si-B alloys at 1450 °C in equilibrium with SiC and B₄C, based on the experimental results. In this regard, the eutectic alloy (3.25 mass % B) is recommended to be used as the new PCM in the graphite container, due to that it produces simple phases and also because it is expected not to deplete any B to the B₄C layer.

Fe–26Si–9B alloy is a promising high temperature phase change material (HTPCM), due to its high heat of fusion, small volumetric change, abundance, and low cost. Additionally, graphite has been identified as a promising candidate for use as a container material for this alloy. In this study, the feasibility of using graphite for Fe–26Si–9B HTPCM is investigated in a pilot-scale. Specifically, 4–5 kg Fe–26Si–9B master alloys were melted in graphite crucibles using an induction furnace, which underwent 2–3 thermal cycles in the temperature range of 1,100–1,375°C. The results showed that SiC and B ₄ C precipitates were formed in the alloys. However, these carbides were found to be present only on the surface of the solidified alloys and not in the main body. Still, the chemical composition of the Fe–26Si–9B alloy remained relatively stable during the thermal cycles. It was also seen that the graphite crucible withstood the temperature cycles without cracking. Therefore, the use of graphite as a container for Fe–26Si–9B phase change material is a promising approach.