Preparation and characterization of diatomite-based form-stable composites with enhanced thermal conductivity for thermal energy storage

Phase change materials (PCMs) can be used to store thermal energy and improve energy efficiency. By integrating PCMs into buildings, excess heat inside the building can be stored, and thus electricity consumption of air conditioning systems can be greatly reduced and electricity can be saved. In this study, a form-stable composite PCM consisting of paraffin eutectic mixture (n-eicosane-n-heptadecane) and diatomite was prepared for thermal energy storage in buildings. The composite PCM was prepared by adding paraffin eutectic mixture into diatomite by direct impregnation method. The morphology, chemical structure, chemical compatibility, thermal properties and thermal stability of the n-eicosan-n-heptadecane/diatomite composite was extensively investigated by SEM, FT-IR spectroscopy, DSC, and TG analysis. FT-IR results showed that there are only physical interactions between n-eicosan-n-heptadecane eutectic mixture and diatomite. DSC results showed that the composite exhibited similar phase change characteristics with the paraffin eutectic mixture. TG analysis results showed that the prepared composite PCM does not decompose up to 100 oC and has good thermal stability. Boron nitride (BN) was added to the composite at different mass ratios (0.5, 1.5, and 2.5%) to increase the thermal conductivity of the composite PCM, and it was found that the thermal conductivity of the composite PCM increased with the added BN amount. In addition, an energy-storing composite plaster was prepared by adding the prepared composite PCM to the gypsum plaster and its thermal performance was tested in a laboratory scale cell. Thermal performance tests showed that the composite could reduce in-room temperature fluctuations due to energy storage and had great potential for energy savings.