engleski

Sol-gel derived, paraffine and silica based phase change microcapsules

The development of energy storage devices receive great attention nowdays. Latent heat storage, most oftenly accomplished through solid-liquid phase transformations, is one of the most attractive. Many phase change materials (PCMs) have been studied for practical use, paraffin waxes being among most promising. The greatest disadvantages of paraffines are low thermal conductivity, leakage and interfacial combination problem with accompanying materials. The solution of those problems can be achieved through the encapsulation of PCMs in microspheres. Usually, microencapsulated PCMs consist of some core–shell structured particles, having a PCM core surrounded by a polymer shell. Choosing an inorganic material such as silica as a shell for the micro-PCMs is a promising idea for enhancing their properties. The aim of this work is to develop inorganic encapsulation technique of PCMs for enhanced performance. Microcapsules have been prepared by utilizing the sol–gel method through an oil-in- water (O/W) emulsion route. The properties, phase- change behavior and microsturcture of novel microencapsulated PCM based on paraffin core and silica shell has been investigated. The feasibility of incorporating prepared microcapsules in gypsum wallboards to increase the wall energy storage capacity was also studied. The paraffin was first dispersed in an aqueous solution to form droplets with the aid of surfactants, which resulted in a stable O/W microemulsion. Silica precursor, tetraethoxysilane (TEOS) has been disolved in ethanol and added to microemulsion. In the course of hydrolysis and condensation processes, silica gel network was formed on the paraffin droplets surface forming silica shell. Fourier transform infrared spectra confirmed that the TEOS gellation was successfull. X-ray diffraction analysis indicated that the paraffin inside the silica microcapsules still retains a good crystallinity. The thermal stability was investigated using simultaneous differential thermal and thermo-gravimetric analysis (DTA/TGA). It was determined that microcapsules have good thermal stability. Optical microscopy and scanning electronic microscopy images suggest that the microcapsules exhibit a spherical morphology with a well-defined core– shell microstructure. Particle size determination pointed out that microcapsules present a large particle size range. The thermal properties were investigated by a differential scanning calorimetry (DSC). The DSC results indicated that the microcapsules thermal properties are in concordance with the ratio of paraffin in composite. The thermal behavior of gypsum doped with prepared samples was studied using self-built equipment for thermal response measurements. Doped material shoved the increase of time required to achieve the final steady state, verifying that the material insulation capacity was enhanced. The silica-microencapsulated paraffin can achieve high encapsulation efficiency, good phase-change performance, and good chemical properties by controlling the loading of paraffin, surfactants and TEOS during the sol–gel process. The incorporation of the microcapsules to the gypsum enhanced material insulation capacity.

Phase change materials ; sol-gel ; paraffine ; silica ; microcapsules

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