Preparation and properties of palmitic acid/SiO2 composites with flame retardant as thermal energy storage materials

Palmitic acid/silicon dioxide (SiO2) composites with flame retardant as thermal energy storage materials were prepared using sol–gel methods. In the composites, palmitic acid was used as the phase change material (PCM) for thermal energy storage, and SiO2 acted as the supporting material. In order to improve flame retardant property of the composites, melamine was added in the composites. Fourier transformation infrared spectroscope (FT-IR), X-ray diffractometer (XRD) and scanning electronic microscope (SEM) were used to determine chemical structure, crystalloid phase and microstructure of palmitic acid/SiO2 composites, respectively. The thermal properties, such as phase change temperature and latent heat, were investigated by a differential scanning calorimeter (DSC). Thermal stability was determined by a thermogravimetric analyzer (TGA). The SEM results showed that palmitic acid was well dispersed in the porous network of SiO2. The DSC results indicated that the composites solidify at 59.20 °C with a latent heat of 60.55 kJ/kg and melt at 59.76 °C with a latent heat of 85.11 kJ/kg when the mass percentage of palmitic acid in the composites was 41.1%. The TGA results showed that addition of melamine improved thermal stability. The microstructure of the charred residue after combustion indicated that the homogeneous and compact charred residue decreased the flammability of the composites.