The Synthesis, Microstructure And Properties Of Calcium Carbonate Encapsulated Senior Aliphatic Alkanes

Phase change material (PCM) is a novel energy storage material which can absorb and release energy on the relative constant temperature (phase transition temperature). In a practical application, encapsulation technique was employed to synthesize phase change microcapsules (micro-PCMs) for the purpose to prevent the leakage of the PCMs during the phase change, meanwhile, enhance the heat transfer efficiency. As an energy storage and temperature regulating materials, microencapsulated phase change is widely used in textile, construction and military.In this paper, we employ n-octadecane and n-eicosane as core material, Calcium Carbonate (CaCO3) as shell, to synthesize the micro-PCMs with inorganic wall. Microstructure observation and properties characterization were further carried out. The main works are as follows:1. n-Octadecane microcapsules with CaCO3shell was synthesized with complex emulsifier of Tween80and Span80by changing the mass ratio of the n-octadecane/CaCl2. The FT-IR and WAXS tests were taken to confirm its chemical composition. Scanning electric micrographs demonstrated that the microcapsules achieved a spherical morphology with a core-shell microstructure. Differential Scanning Calorimetry investigated that the microcapsulated n-octadecane showed a good phase-change performance with a high thermal storage capability, and both of the encapsulation ratio and encapsulation efficiency increased with rise of the n-octadecane/CaCl2mass ratio. The microcapsules exhibited a bimodal crystallization peak during its cooling process, namely P peak and a peak. The existed a peak is because the shell act as nucleation agent, and induce the heterogeneous nucleation. And the P peak is generated by the homogeneous nucleation by the n-octadecane itself. The heterogeneous nucleation lead to a higher crystallization rate, and accelerate the thermal response further. The thermal stability and serving durability were also enhanced under the protection of compact CaCO3shell.2. n-eicosane/CaCO3microcapsules have been synthesized through a self-assembly method. The resultant microcapsules exhibited a spherical morphology under a lower concentration of sodium dodecyl-benzenesulfonate(SDBS) surfactant, and the rhombohedral morphology arose with the increase of the concentration of SDBS. The inner shape of each microcapsule is in accordance with its outer morphology. The crystalline transition was occurred when the synthesis was taken at the surfactant concentration of3.0mmol/L. Wide-angle X-ray Diffraction confirmed that the rhombohedral microcapsules achieved a calcite CaCO3 shell, while the spherical ones were encapsulated by the vaterite CaCO3. The characterization of DSC heating-cooling cycle demonstrated that the encapsulated n-eiscosane performed good phase change properties, and those microcapsules who had vaterite shells got higher encapsulation ratio, compared to those with calcite ones. Meanwhile, the CaCO3shell which took the role of nucleating agent, induced the heterogeneous nucleation of n-eicosane, enhanced the crystallinity of n-eicosane in a-form, and led to an increase in crystallization temperature. Thus, owing to the encapsulation of CaCO3. the resultant microcapsules achieved a rapid thermal response, and suppressed undercooling of inner n-eicosane at the same time.