关键词: 膨胀石墨, 硬脂酸, 定形, 相变, 复合材料, 制备, 热物性, 热稳定性

Abstract:

A modified method is proposed to prepare shape-stabilized phase change composites by employing “heating adsorption of liquid stearic acid (SA) into expanded graphite (EG) matrix and compressing stable-shape composite”. Sixteen samples with different EG contents and packed densities are prepared using SA as the phase change material and EG as porous matrix. The microstructures, thermal properties and thermal stabilities of different EG/SA samples are analyzed and investigated. Scanning electron microscopy is first used to observe the microstructures of EG/SA samples and the results show that SA is well dispersed into the graphite flakes and the laminar structures become more inerratic with increasing packed density. The data obtained from differential scanning calorimetry show that the EG/SA composites nearly have no supercooling problem. Moreover, the addition of EG and compressing operation have negligible effect on the latent heat and phase change temperature of pure SA. Hot-disk thermal constants analyzer is used to evaluate the effect of EG content and packed density on the thermal conductivity and the anisotropy of the EG/SA samples, including axial and radial thermal conductivity. The results show that both axial and radial thermal conductivity can be enhanced significantly by using the additive of EG, and the radial thermal conductivity is as high as 23.77 W·m^-1·K^-1. The difference between axial and radial thermal conductivity becomes more remarkable by increasing the packed density, and the largest difference reaches 5.4 times. Finally, the thermal stability of EG/SA samples is evaluated by repeating charging and discharging processes of SA. The samples with relatively high density or low EG content are susceptible to liquid leak. However, the thermal stability of EG/SA composites can be regulated by optimizing the combination of EG content and packed density. The shape-stabilized phase change composites present better comprehensive performance with EG content about 25% and packed density about 950 kg·m^-3. In comparison with the traditional method for preparing shape-stabilized phase change composite, the proposed method can improve the overall thermal performance of composites, and the thermal conductivity can be enhanced more than 130 times higher than that of pure SA.

Key words: expanded graphite, stearic acid, shape-stabilized, phase change, composites, preparation, thermophysical properties, thermal stability