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SUMMARYA novel form-stable composite as phase change material (PCM) for thermal energy storage was prepared by absorbing stearic acid (SA) into halloysite nanotube (HNT). The composite PCM was characterized by TEM, FT-IR and DSC analysis techniques. The composite can contain SA as high as 60 wt% and maintain its original shape perfectly without any SA leakage after subjected to 50 melt-freeze cycles. The melting temperature and latent heat of composite (SA/HNT: 60/40 wt%) were determined as 53.461C and 93.97 J g À1 by DSC. Graphite was added into the SA/HNT composite to improve thermal storage performance, and the melting time and freezing time of the composite were reduced by 65.3 and 63.9%, respectively. Because of its high adsorption capacity of SA, high heat storage capacity, good thermal stability, low cost and simple preparation method, the composite can be considered as cost-effective latent heat storage material for practical application.

The layered oxides demonstrate a lower thermal conductivity than their non-layered counterpart materials. 1,2 The thermal conductivity of the layered oxides has a strong anisotropy. For example, Bi 2−x Pb x Sr 2 Co 2 O y (x = 0, 0.4, and 0.6) has an out-of-plane thermal conductivity of 0.4 W/m K at room temperature (RT), 3 while its in-plane thermal conductivity is up to 3.5 W/m K. 4 Interestingly, Shen Y et al reported that the low thermal conductivity of layered Bi 4 Ti 3 O 12 persisted up to at least 1000°C despite a change in the crystal structure at 675°C. This work indicates that the low thermal conductivity of the layered Bi 4 Ti 3 O 12 is associated with the layered structure of the compound rather than the detailed arrangement of