Improvement in thermal endurance of D-mannitol as phase-change material by impregnation into nanosized pores

• D-mannitol was used as phase change material.
• D-mannitol was supported into nano-sized pore of porous SiO2.
• The melting point of D-mannitol was decreased with smaller pore of porous SiO2.
• Thermal endurance of D-mannitol was improved.

This paper describes the control of the melting point and improvement of the thermal endurance of D-mannitol (melting point Tm = 440 K) as a phase-change material (PCM) by vacuum impregnation of the PCM into nanosized pores of porous SiO2 grains. First, we examined the effects of the average pore size (DP) of porous SiO2 on Tm and latent heat (L) of PCM/SiO2 composites. Second, we investigated the thermal endurance of the composites using constant temperature kinetics based on L of the PCM and composites. Third, we performed cyclic tests of melting and freezing on the composite to evaluate leakage of the PCM. Thermophysical properties of the samples were measured by differential scanning calorimetry, and the following results were obtained: (1) The impregnation ratio of the composites was 0.91–0.99; therefore, almost all pores were completely filled with the PCM. (2) Tm shifted to lower temperature with smaller DP, reaching 413 K in case of the PCM/SiO2 composite with a DP of 11.6 nm (3) Tm was derived as a function of DP from the Gibbs–Thomson equation taking into account the existence of a nonfreezing layer on the surface of the pore wall. (4) The duration of thermal degradation of the PCM/SiO2 composite with DP = 11.6 nm was three times longer than that of the pure PCM at a temperature that is 10 K more than each melting point. (5) The PCM/SiO2 composite with DP = 11.6 nm can use as a shape-stable PCM composite without leakage of PCM.