The Use of Fe-26Si-9B Alloy as Phase Change Material in Si<inf>3</inf>N<inf>4</inf> Container

Abstract

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.