Lauric acid/refractory clay/expanded graphite composites for improved thermal energy storage characteristics

• A series of composite phase change materials (PCMs) were prepared by using a refractory clay (RC). • Refractory clay (RC) composed of mainly SiO 2 , Al 2 O 3 and TiO 2 was used as support matrix. • Lauric acid (LA) was incorporated into RC support by solvent-assisted impregnation method. • The properties of the composite PCM were improved by highly conductive expanded graphite particles. • The shape-stabilized LA/RC composites are possible candidates for energy storage applications. Refractory clays (RC) are aluminosilicate based inorganic materials, which have unique properties such as low cost, high thermal stability, chemical resistance, mechanical strength and absorbability. In this study, RC, mainly composed of SiO 2 (56.01%), Al 2 O 3 (41.96%) and TiO 2 (1.26%), was explored as a thermally stable and low-cost supporting material for development of LA based shape-stabilized composite PCMs, while expanded graphite (EP) was employed to develop heat transfer performance with maintaining shape stability. A series of LA/RC composites were prepared by solvent assisted impregnation method, and leakage tests were conducted to evaluate the shape-stabilization property. The morphological, chemical, thermal properties and phase change characteristics of the prepared composites were determined by scanning electronic microscope (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). The maximum PCM weight fraction among the prepared composites was found to be 40 wt% without any leakage and this composite demonstrated good thermal reliability after repeated heating–cooling cycles. The latent heats and temperatures of the composite PCM were measured as 64.2 J/g and 43.46 °C for melting and 66.0 J/g and 41.77 °C for crystallization. The shape-stable composite PCM was modified with highly conductive EP particles with the aim of improving heat conduction property and eliminating drawbacks of low thermal conductivity due to RC support. The shape-stable LA/RC/EP composite displayed improved thermal conduction properties thanks to loading 5 wt% EP, while latent heats slightly decreased (63.6 J/g for melting and 61.7 J/g for crystallization) in comparison with undoped composite. LA/RC/EP composite is a promising energy material for passive energy storage applications such as solar energy storage and thermoregulation of buildings where shape stability and improved heat transfer are demanded under practical constraints.