Preparation, Characterization And Properties Of Solid-solid Composite PCMs

As the development of economic, shortage of fossil fuel and environmental pollution has provided an impetus to develop renewable energy sources, as well as materials for energy storage. Phase change materials (PCM) have attracted attention of researchers and engineers in different fields due to its high energy storage density and nearly invariable operating temperature. Until now, PCMs have been widely used in the area of aviation, passive solar energy storage, building heating system, and recovery of industry waste heat.It is well known that bulk PCM is not easy to handle in practical application due to the leakage problem. Therefore, some attempts, such as blocking, grafting, and microencapsulating have been developed. Nevertheless, there are some limitations for using polymeric matrix and shell. For example, noxious gas release, flammability, poor thermal stability and heat conductivity, low mechanical strength of polymer maxtric restrict its application seriously. In contrast, inorganic materials such as silica, kaolinite, and attapulgite are nonflammable, and possess higher mechanical strength, higher thermal conductivity and better chemical resistance compared with polymer. In this paper, eutectic/silica microcapsules, kaolinite and attapulgiate based form-stable PCMs were parepared. FTIR, XRD, DSC, SEM, TEM, TG were applied to investigate the structure, morphology and thermal properties of obtained solid-solid PCMs. The results are shown as below:(1) The eutectic transition temperature of mixtures of SA and OA was52℃, the ratio of SA to OA was48%to52%, and the latent heat of eutectic was216.9J/g. It was found that there was no chemical reaction between the functional groups of the components during the preparation process and the obtained particles had clear core-shell structure with smooth and compact surface. The crystalline structure of eutectic did not change after encapsulated, while the crystallinity decreased. The maximum latent heat of microcapsules kept solid-solid properties was123.1J/g and the melting temperature was54℃, respectively. The particle size distribution decreased as the agitation speed increased. When the agitation speed was1800r/min, the particle sizes of microcapsules distributed in the range of1-10μm. (2) The basal spacing of kaolinite increased from0.7178nm to1.1238nm and the intercalation rate reaches up to92%. The optimum adsorption ratio of paraffin, lauric acid and stearic acid in kaolinite and intercalted kaolinite were47%,38%,36%and52%,42%,39%respectively. The specific areas, pore size of kaolinite, intercalated kaolinite, and paraffin/intercalated kaolinite were14.32m2/g,30-100nm, and19.35m2/g,40-120nm, and16.56m/g,40-80nm respectively. The Tm and ΔHm of paraffin/intercalated kaolinite were50.2℃and99.3J/g, indicating it possessed relatively large latent heat and suitable phase change temperature.(3) Attapulgite has a fibrous structure with an average length of0.5-2m, and an average diameter of15-25nm, which can be classified as one dimemsion nano materials. The maximum adsorption ratio of octadecanol in composite was52%and the Tm and ΔHm were measured to be108J/g and54.9℃, which can be used as cooling system of portable electronic devices, military electronic systems and passive solar heating system.