A new low-cost high-temperature shape-stable phase change material based on coal fly ash and K2CO3

Abstract The shape stable phase change materials (SSPCMs) consisting of coal fly ash (CFA) and potassium carbonate (K2CO3) are promising candidates for high temperature thermal storage applications, owing to their low price, high melting enthalpy and low corrosivity of K2CO3. Nevertheless, the chemical reactions between K2CO3 and CFA at high temperature limit its application. To solve this problem, in this work, a new two-step method for preparing SSPCMs containing K2CO3 and CFA was proposed. Firstly, the CFA was successfully modified by K2CO3 with a mass ratio of 3:2. The main phase of the modified CFA was changed into potassium aluminum silicate (KAlSiO4). Then the SSPCMs were synthesized using the modified CFA and K2CO3. The latent heat and thermal conductivity of the prepared SSPCMS increased with the increase of salt content. The SSPCMs with potassium carbonate contents of 50 wt% (SSPCM-55) and 60 wt% (SSPCM-46) maintained good shape without cracks after the sintering processes. In addition, they showed a good cyclic stability in the 150 times thermal cycle tests in terms of mass, latent heat and chemical compatibility. The SSPCM-46 showed the best performance considering both heat transfer and energy storage density, and is promising to be used as a low-cost high-temperature PCM.