OBTAINING AND PROPERTIES OF NANOSCALE SOLID-STATE HEAT STORAGE WITH CARNAUBA WAX

Abstract

Latent thermal energy storage using phase change materials has attracted interest in the use of solar and other types of energy due to their ability to provide high density lateral energy storage. Materials with a latent heat of storage have become attractive for their use in many branches of human activity. However, the materials use is often limited by problems of low thermal conductivity, the transition from a solid to a molten state causes difficulties in storing materials in a container, and special heat exchangers are needed to increase the energy cost. The solution to the above problems may be to create solid-state, form-stable heat storage elements. In this work, a number of shape-stable materials with a phase transition were obtained from melts by mixing halloysite nanotubes with carnauba wax in order to improve the heat accumulation characteristics. Halloysite nanotubes were mixed at elevated temperatures with carnauba melted wax and rapidly cooled to prevent the nanotubes sedimentation. As a result, a series of solid wax/nanotube samples were prepared with weight ratios of 70/30, 60/40 and 50/50. Pure wax showed a accumulation heat of the solid-to-liquid phase transition of 189.09 J/g. Carnauba wax has a latent heat greater by about 25 % compared to paraffin. Composite materials had significantly lower latent heat, respectively, 99.39 J/g for 70/30, 90.25 J/g for 60/40, and 81.26 J/g for 50/50 samples. Elemental mapping of the nanomaterial revealed a nanotubes uniform distribution in the wax. According to the data of X-ray analysis, as a result of the composite materials preparation, the components did not form new crystalline phases, but they were physical mixtures. When heated, the components did not chemically interact with each other, which is useful for the accumulation of thermal energy by materials. Analysis of the IR spectra of the samples confirmed the change in the absorption bands of functional hydroxyl groups at 3696 sm–1 (Al–O–H) and 3621 sm–1 (Si–O–H). In primary nanotubes, the intensities ratio of silanol to aluminol groups is greater than unity, while in the composite it is already less than this value. This manifestation can be explained by the fact that, during the wax melting, the interaction of wax molecules on the outer surface of the nanotubes occurs. Bibl. 16, Fig. 5.