Thermophysical properties and thermal cycling behaviour of RT54 HC nanocomposite phase change materials containing samarium oxide

This study examines the effects of Sm 2 O 3 content on the thermophysical properties and thermal cycling behaviour of RT54 HC phase change composites. Formulations containing 5–20 wt% Sm 2 O 3 were prepared using vacuum assisted melting, magnetic stirring, and bath sonication. Structural and morphological analyses were combined with calorimetric, thermal conductivity, and thermogravimetric measurements. Samples underwent up to 10,000 melting and solidification cycles between 35 and 75 °C. The characteristic RT54 HC spectral and diffraction features remained observable after nanoparticle incorporation, while the phase change temperature range was largely retained across the formulations. Thermal conductivity measured on compacted powders at 25 °C increased from 0.186 W/(m·K) for pristine RT54 HC to 0.282 W/(m·K) at 20 wt% Sm 2 O 3 , corresponding to a 51.6% enhancement. At 70 °C, the corresponding conductivities with the PCM matrix in the molten state were 0.178 and 0.260 W/(m·K), giving a 46.1% enhancement. The highest first cycle mean liquid region C p , evaluated over 62–75 °C, was 4.64 J/(g·K) at 12.5 wt% Sm 2 O 3 , representing a 75.6% increase. For this formulation, the melting and solidification enthalpies changed from 181 to 180 J/g initially to 165 and 165 J/g after 10,000 cycles, while the mean liquid region C p decreased to 3.28 J/(g·K). Thermogravimetric measurements characterized degradation during programmed heating under nitrogen. The results identify different compositions for maximum thermal conductivity and C p , together with changes in storage capacity during cycling. These findings provide a material characterization basis for subsequent evaluation in thermal energy storage systems.