Surface Roughness-Governed Shape Stability of the Coal Fly Ash-Based Phase Change Material: Molten Salt Processing and Thermal Properties

Coal fly ash (FA) valorization is of great significance and sustainable interests to addressing the current environmental challenges faced by coal power industry. Herein, this work attempted a novel molten salt Na2CO3 treatment for processing FA into a robust matrix to support lauric acid (LA) toward construction of latent phase change composite. Their micromorphology, physiochemical, and thermal properties were monitored with scanning and transmission microscopy, X-ray diffraction and FT-IR spectroscopy, differential scanning calorimetry, among others. As Na2CO3 dosage increased from 20% to 40%, the FA experienced firstly higher loss of SiO2 and then substantial loss of Al2O3, and yet exhibited merely varied porosity. Then, both the composites revealed a maximum LA content of 20% that doubled that of pristine FA. Nevertheless, the optimal composite was disclosed with thermal conductivity of 0.5668 W/mK, which was 69% higher than its FA-based counterpart. It was proposed that the surface roughness evidenced by the formation of tremendous grooves and gaps during thermal alkaline processing were accountable for the promoted carrying capacity toward organic component. Furthermore, the latent phase change composite revealed excellent durability, including negligibly varied phase transition temperature and enthalpy even after 1500 thermal cycling, which promised great interest in passive building cooling. Meanwhile, the finds here led to a new understanding into the structural origin of adsorption capacity by inorganic FA, and may provide guidance for better exploration of its characteristics for other applications.