The Study Of Synthesis And Properties Of Silica Microencapsulated N-Alkanes Phase Change Materials Based On Sodiun Silicate

This paper includes two parts. The frist part is about the prapreration of microencapsulated n-octadecane with silica wall in a sol-gel process using sodium silicate as a precursor. Factors about stability of n-octadecane emulsion and pH values of reaction solution have been disscussed. The chemical composition of the synthesized microcapsules and good crystallinity for the n-octadecane inside silica microcapsules were confirmed by Fourier transform infrared spectra and wide-angle X-ray diffractometer respectively. Scanning electric micrographs indecated that the microencapsulated n-octadecane acquired at pH2.95-3.05presents a well-defined core-shell microstructure and a perfect spherical morphology. Moreover, phase change characteristics of the microcapsules were characterized by differential scanning calorimeter (DSC), the results demonstrated that microcapsules Synthesized at pH2.95～3.05and mass ratio of n-octadecane/sodium silicate at1-1.5exhibits good phase change performance and achieves a high rate of encapsulation and encapsulation efficiency. The encapsulation of n-octadecane with smooth and compact silica wall can improve the thermal stability of the microcapsules by holding back inside n-octadecane from evaporating.The second part is with respect to the preparation of a series of n-alkanes/silica compositesas the form-stable phase change materials through sol-gel synthesis using sodium silicate as a silica precursor. Fourier transform infrared spectroscopy confirmed the chemical compositions and structures of the synthesized composites. The Scanning electric micrographs present an irregularly spherical morphology of the n-alkanes/silica composites, and transmission electric micrographs indicated that the n-alkanes have been well encapsulated by silica. Analysis by Differential scanning calorimetric desmonstrated that the phase change behaviors and characteristics of the n-alkanes/silica composites depend on the carbon atom number of n-alkanes to a large extent.The parity of the carbon atom number of n-alkanes made the crystal morphology and phase transition behavior different, without affecting the phase transition enthalpy and heat storage capacity of the n-alkanes/silica composites. Due to the protection of silica wall toward the encapsulated n-alkanes, the n-alkanes/silica composites can present some white powders macroscopically, and achieved a high thermal stability, low supercooling, and good work reliability. Owing to the easy availability and low-cost of sodium silicate, this synthetic technology can provide a new technical route for industrial manufacture and broaden the applications of the Phase change microcapsules in garment and building energy conservation areas.