Insight into the effect of crystallographic structure on thermal conductivity of kaolinite nanoclay

摘要

Thermal conductivity plays an important role in thermal performances of latent heat thermal energy storage (LHTES) systems with phase change materials (PCMs). With respect to the significance of kaolinite nanoclay in PCMs manufacture, previous works have paid much attention to the effect of physicochemical properties such as morphology of kaolinite on thermal conductivity. However, the relationship between the evolution of crystallographic structure and thermal conductivity has not been researched. In this work, this correlation was systematically elucidated through experimental investigation and theoretical analysis using thermogravimetry and differential scanning calorimetry (TG/DSC), X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). The results indicated that poorly ordered kaolinite possessed a low thermal conductivity, and particularly crystallinity index and conductivity showed a clear regression relationship. Further investigation determined that lower conductivity was attributed to the ill structured geometrical configuration of silicon- and aluminum-oxygen units, which resulted in an increasing number of phonon-defect scattering events, and thus limited the mean free path of phonons in kaolinite lattices. This was contributed to the low thermal conductivity based on the characteristic property of phonon heat conduction.