Thermophysical properties of eutectic Fe-57Si ultra-high-temperature metallic phase change material

Abstract A binary Fe-57Si (mass%) eutectic alloy is being considered as a potential candidate for ultra-high-temperature metallic phase change material (PCM) applications in latent heat thermal energy storage systems (LHTES). The high melting point of 1213 °C makes it suitable thermophotovoltaic conversion, a developing heat-to-electricity solid-state technique that benefits from high temperatures. Such high-temperature storage can be achieved using concentrated solar power (CSP). In this work, pendant drop (PD) and differential scanning calorimetry (DSC) methods were applied to examine the solid- and liquid-state thermophysical properties. The results show the onset of the melting and solidification, respectively, at 1221 °C and 1190 °C a heat of fusion of $$930\, \text{J}\,\text{g}^{-1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>930</mml:mn> <mml:mspace/> <mml:mtext>J</mml:mtext> <mml:mspace/> <mml:msup> <mml:mtext>g</mml:mtext> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> , a density amounting $$4.0669\, \text{g}\,{\text{cm}}^{-3}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>4.0669</mml:mn> <mml:mspace/> <mml:mtext>g</mml:mtext> <mml:mspace/> <mml:msup> <mml:mrow> <mml:mtext>cm</mml:mtext> </mml:mrow> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> , a volumetric expansion upon solidification of $$-0.372\%$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>0.372</mml:mn> <mml:mo>%</mml:mo> </mml:mrow> </mml:math> and a surface tension $$\gamma =-0.1861T+1093.8\, \text{mN}\,{\text{m}^{-1}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>γ</mml:mi> <mml:mo>=</mml:mo> <mml:mo>-</mml:mo> <mml:mn>0.1861</mml:mn> <mml:mi>T</mml:mi> <mml:mo>+</mml:mo> <mml:mn>1093.8</mml:mn> <mml:mspace/> <mml:mtext>mN</mml:mtext> <mml:mspace/> <mml:msup> <mml:mtext>m</mml:mtext> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> . The combined results indicate that the Fe-57Si alloy can achieve a volumetric energy storage capacity of up to 1.05 MWh m −3 under experimental conditions operating at temperature range of 1150–1250 °C. Further investigations are needed to investigate the long-term performance of Fe-57Si. The first challenge is to develop containment strategies, critical due to the alloy’s potential reactivity. Then, the solution should be validated upon cycling to evaluate the material stability over repeated phase transitions.