The present study prepared nanocomposite phase change materials (PCMs) based on calcium chloride hexahydrate (CaCl2·6H2O) with gamma aluminum oxide (γ-Al2O3) nanoparticles to characterize phase change behavior, such as the supercooling degree, phase change temperature, latent heat, thermal conductivity, and thermal stability. Results demonstrate that thermal conductivity and heat transfer of the CaCl2·6H2O/γ-Al2O3 nanocomposite PCMs are significantly enhanced and supercooling of CaCl2·6H2O/γ-Al2O3 nanocomposite PCMs is suppressed. Moreover, a 50 run cycling test verifies that the CaCl2·6H2O nanocomposite PCMs contained with 1 wt % γ-Al2O3 possesses enhanced thermal behavior. The degree of supercooling is within the range of 0.3–1.1 °C; the maximum reductions in the latent heat is 5.9%; and no phase segregation was observed. The CaCl2·6H2O/γ-Al2O3 nanocomposite PCMs presented acceptable thermal reliability, chemical stability, and heat transfer characteristics, thereby reflecting its acceptability for low-temperature solar thermal energy storage applications.

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Porous Al2O3@graphite foams (PAGFs) were directly prepared by a particle-stabilized foaming method, with 40 vol % Al2O3 particles and different proportions of sucrose. The as-prepared PAGFs demonstrate three-dimensional interpenetrating structures and high porosities according to SEM images, with the porous morphology being markedly influenced by the concentration percentage of sucrose. Additionally, the PAGFs could be successfully impregnated with paraffin, reaching a maximum enclosed ratio (φ) of 66 wt % without any leakage. Differential scanning calorimetry measurement showed that the latent heat of the composites of paraffin/PAGF (PAGFPs) reach maxima of 105.76 and 105.98 J/g after 200 cycles of melting/freezing. Thermogravimetric analysis, Fourier transform infrared spectroscopy, and thermal cyclic tests demonstrated good thermal and chemical stability and good thermal reliability for the as-prepared form-stable PAGFPs. Our results also confirmed that a layer of ordered graphite film is formed on the surface of Al2O3 particles after sintering at 1600 °C. As a result, the specific surface area of PAGF is 13 times greater than that of the foams without coating graphite. Meanwhile, the thermal conductivities of the PAGFPs reached a maximum of 0.76W/m·K, which was 3.62 times that of pristine paraffin. In conclusion, we demonstrated here the design and preparation of form-stable composite phase change materials with controllable porous structures and superior thermal and chemical stabilities and reliabilities for heat energy storage applications.

A striking contrast in the thermal conductivities of polyethylene glycol (PEG)/diatomite form-stable phase change composite (fs-PCC) with single-walled carbon nanotubes (SWCNs) as nano-additive has been reported in our present study. Compared to the pure PEG, the thermal conductivity of the prepared fs-PCC has increased from 0.24 W/mK to 0.87 W/Mk with a small SWCNs loading of 2 wt%. SWCNs are decorated on the inner surface of diatomite pores whilst retaining its porous structure. Compared to PEG/diatomite fs-PCC, the melting and solidification time of the PEG/diatomite/SWCNs fs-PCC are respectively decreased by 54.7% and 51.1%, and its thermal conductivity is 2.8 times higher. The composite can contain PEG as high as 60 wt% and maintain its original shape perfectly without any PEG leakage after subjected to 200 melt-freeze cycles. DSC results indicates that the melting point of the PEG/diatomite/SWCNs fs-PCC shifts to a lower temperature while the solidification point shifts to a higher temperature due to the presence of SWCNs. Importantly, the use of SWCNs is found to have clear beneficial effects for enhancing the thermal conductivity and thermal storage/release rates, without affecting thermal properties, chemical compatibility and thermal stability. The prepared PEG/diatomite/SWCNs fs-PCC exhibits excellent chemical and thermal durability and has potential application in solar thermal energy storage and solar heating.

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