低熔点氯盐/膨胀石墨复合材料的制备及传蓄热性能研究

Preparation and heat transfer and storage properties oflow melting point chloride/expanded graphite composites

以成型膨胀石墨(EG)为骨架,低熔点四元氯盐(LiNaKZn-Cl)为相变材料,采用真空浸渍法制备了低熔点氯盐/膨胀石墨(LiNaKZn-Cl/EG)相变复合材料,通过扫描电子显微镜(SEM)、X射线衍射仪(XRD)、热重分析仪(TG)对相变复合材料的微观形貌、结晶结构和热稳定性进行了表征,利用差示扫描量热仪(DSC)对相变复合材料的熔点、熔化焓和比热容进行了测量,利用激光导热仪(LFA)进行了热扩散系数的测量。研究结果表明,LiNaKZn-Cl成功浸渍到EG内部,且EG维持了完整的孔结构。由于EG的异相成核的作用LiNaKZn-Cl/EG熔点为169.0℃较LiNaKZn-Cl略有下降。LiNaKZn-Cl/EG保留了EG骨架高热导率的特性,在室温下面向和法向的热导率分别为53.7和23.1 W/(m·K)。LiNaKZn-Cl/EG熔化焓为63.3 J/g,LiNaKZn-Cl在LiNaKZn-Cl/EG中高质量占比保证了相变复合材料的储热能力。制备的LiNaKZn-Cl/EG热稳定性良好,使用温度可达500℃,热导率较LiNaKZn-Cl有了极大的提升,可提高中温储热领域的充放热效率。

The low-melting point chloride salt/expanded graphite(LiNaKZn-Cl/EG)phase change composites were prepared by vacuum impregnation using anisotropically formed expanded graphite(EG)as the skeleton and low-melting point quaternary chloride salt(LiNaKZn-Cl)as the phase change material,and the phase change composites were characterized by scanning electron microscopy(SEM),X-ray diffractometer(XRD)and thermogravimetry(TG).The microscopic morphology,crystalline structure and thermal stability of the phase change composites were characterized by scanning electron microscopy(SEM),X-ray diffractometer(XRD)and thermogravimetry(TG),the melting point,melting enthalpy and specific heat capacity of the phase change composites were measured by differential scanning calorimetry(DSC),and the thermal diffusion coefficient was measured by laser flash analysis(LFA).The results showed that LiNaKZn-Cl was successfully impregnated into the interior of EG,and EG maintained an intact pore structure.The melting point of LiNaKZn-Cl/EG is 169.0℃with a slight decrease compared to that of LiNaKZn-Cl due to the heterogeneous nucleation of EG.LiNaKZn-Cl/EG retains the high thermal conductivity of the EG skeleton,with 53.7 W/(m·K)and 23.1 W/(m·K)in the downward and normal directions,respectively,at room temperature.The melting enthalpy of LiNaKZn-Cl/EG is 63.3J/g,and the high mass ratio of LiNaKZn-Cl in LiNaKZn-Cl/EG ensures the heat storage capacity of phase change composites.The prepared LiNaKZn-Cl/EG is thermally stable and can be used at temperatures up to 500℃.The thermal conductivity is greatly improved compared with that of LiNaKZn-Cl,which can improve the efficiency of heat charging and discharging in the field of medium temperature thermal storage.