Designing new ultra-high temperature phase change materials from the Fe-Si-B system for thermal energy storage density above 1 MWh/m3

• Re-assessment of Fe-Si-B phase diagram in the pursuit of new PCMs. • Pre-selection of new PCM candidates competitive to already developed Fe-26Si-9B. • Characterization of microstructure (SEM/EDS) and heat of fusion (DSC). • The Fe-46Si-5B alloy exhibited experimental stored energy density above 1 MWh/m 3 . New ternary Fe-Si-B alloys were developed as potential metallic phase change materials (PCMs) for application in ultra-high temperature latent heat thermal energy storage systems (LHTES). By a thermodynamic re-assessment of the Fe-Si-B system, three new Si-rich (approx. 40–50 wt%) compositions were pre-selected for further analyses. The new alloys can provide very high energy density (even above 1 MWh/m 3 ) at melting temperatures around 1150–1200 °C. Furthermore, new PCM candidates have twice lower B content than already developed Fe-26Si-9B alloy, what is beneficial from the economic point of view. For the sake of experimental validation, the PCM candidates were produced by the arc melting technique. The outputs of thermodynamic calculations were verified in detailed microstructural studies and differential scanning calorimetry experiments. In the case of the newly developed Fe-46Si-5B and already designed Fe-26Si-9B alloy, the energy density higher than 1 MWh/m 3 was experimentally confirmed.