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a b s t r a c tWe developed shape-stabilized phase change composites (PCCs) for building materials with high heatstorage density by vacuum impregnation of the phase change material (PCM) octadecane into mesoporous SiO 2 . We examined the effects of the average pore size of mesoporous SiO 2 on the melting point and latent heat of the PCCs. Cyclic tests of melting and freezing were performed to evaluate leakage and degradation of the PCCs. The thermophysical properties of the PCCs were measured by differential scanning calorimetry, and the following results were obtained: (1) The impregnation ratio of the composites was above 0.95; therefore, almost all pores were completely filled with PCM. (2) The melting point of the PCMs decreased with decreasing average pore diameter, and the melting point was established as a function of average pore diameter from the Gibbs-Thomson equation, taking into account the existence of a nonfreezing layer on the surface of the pore wall. (3) The octadecane/mesoporous SiO 2 composites retained the full amount of impregnated PCM, even after cyclic heating and cooling.

To enhance the thermal conductivity of phase change materials (PCM) such as sugar alcohol and molten salts, the preparation of a phase change composite (PCC) with a PCM and a filler with high thermal conductivity has been widely investigated. Although many reported PCCs have high thermal conductivity, the stability during thermal cycling endurance is often too low for practical use. This paper describes the development of a PCC with both high thermal conductivity and high cyclic durability. The PCCs were prepared by a hot-pressing method. Erythritol (melting point: 118°C, thermal conductivity: 0.73 Wm-1 K-1) was used as a PCM, and carbon fiber (thermal conductivity: 900 Wm-1 K-1 in the fiber direction) and indium particles (thermal conductivity: 82.8 Wm-1 K-1) were used as the high thermal conductivity fillers. The effective thermal conductivity of the PCC was measured using the laser flash method and the network structures were analyzed using energy dispersive spectroscopy and scanning electron microscopy. Thermal cycling tests through the melting and solidification phases of the erythritol were performed to investigate the cyclic durability of the PCCs. We found that the indium particles melted during hot pressing, welding together the carbon fiber to produce a stable percolating network, which significantly enhanced the thermal conductivity and cyclic endurance of the PCCs.