Fe-26Si-9B (wt per cent) alloy has been identified as a potential high-temperature phase change
material (PCM) due to its attractive properties, such as its high latent heat of fusion and low
volumetric change during solid/liquid transition. For the successful utilisation of this alloy into thermal
energy storage (TES) systems, the development of a cost-effective production method is essential.
Presently, the Fe-26Si-9B alloy is produced by mixing FeSi alloys with either pure boron element or
FeB alloys. However, the use of pure boron is financially prohibitive, and the carbothermic reduction
results in high greenhouse gas emissions and high energy consumption in the production of FeB
alloys. In this regard, our study proposes a silicothermic reduction method to produce Fe-26Si-9B
PCM by using FeSi alloys and B2O3-based oxides. Accordingly, the influence of various parameters
on the production process was investigated, including operating temperature, holding time, B2O3
content in the added oxides, and initial Slag/Metal (S/M) ratio. Based on the experimental results,
the optimal parameters for producing FeSiB alloys with over 9 wt per cent boron were determined.
Consequently, it was documented that the FeSi alloys and the added oxides enriched with 50–
65 wt per cent B2O3 should be subjected to temperatures ranging from 1550–1650°C, maintain an
initial S/M ratio exceeding 1, and ensure a holding duration beyond 1 hr. Moreover, the energy
consumption of this process was estimated to be ~1.86 MWh/t metal and the mass loss was lower
than 7 per cent. Therefore, silicothermic reduction offers a sustainable approach for producing FeSiB
alloys with a boron content above 9 wt per cent.