LAUSR

Abstract In previous work, a metastable miscibility gap was identified and exploited in the C-Al binary phase diagram, with 50% by volume of either Al or Al-12.7% Si phase change material (PCM) dispersed in a graphitic matrix. These newfound thermal energy storage (TES) materials have high thermal conductivity (∼140 W/mK) and energy densities in the region of 1 MJ/L for ΔT = 100 °C. The main threat to the longevity of the materials is that their use at elevated temperature may precipitate the equilibrium carbide, Al4C3 which would diminish the amount of Al available to act as a PCM. This work presents the effects of extended thermal cycling over the intended use range to test its effect on integrity, phase composition and microstructure of the two candidate materials. A small initial mass loss from the 5 g samples due to the loss of metal particles directly in contact with the surface was observed and which had stabilised after 50–100 cycles. The mass loss is accompanied by a small thermal capacity loss in DTA which also stabilised in the first 50–100 cycles. Both the mass loss and capacity reduction are expected to be greatly reduced in full scale storage modules due to the much smaller surface area to volume ratio (∼0.1) compared with that for the samples used here (∼4). The absence of X-ray diffraction peaks from the carbide Al4C3 in data from the cycled materials and their continued strong latent heat DTA signal strongly suggest that the materials are suitable for long-term use in thermal energy storage applications.