Form-stable LiNO₃–NaNO₃–KNO₃–Ca(NO₃)₂/calcium silicate composite phase change material (PCM) for mid-low temperature thermal energy storage

Graphical abstract: The figure (a) displays the microstructure of calcium silicate and the inset figure is the LiNO₃–NaNO₃–KNO₃–Ca(NO₃)₂/calcium silicate composite PCM. Calcium silicate is used as a porous skeleton material which could absorb large amounts of the nitrate PCM in voids and prevent the PCM from leakage during phase change process. Figure (b) shows the heat capacity of the composite PCM and the inset figure is the DSC curve of the composite. It indicates that this composite has a low melting point (103.5 °C) and good energy storage property. Based on the novel LiNO₃–NaNO₃–KNO₃–Ca(NO₃)₂/calcium silicate composite PCM, this work involves fabrication process, thermal and microstructural characterization, and chemical and physical stability measurements. - Highlights: • A novel LiNO₃–NaNO₃–KNO₃–Ca(NO₃)₂/calcium silicate composite PCM was prepared. • It has a low melting point (103.5 °C) and could remain stable until 585.5 °C. • It could keep form-stable without leakage during phase change process. • Thermal conductivity of the composite PCM reaches up to 1.177 W m⁻¹ K⁻¹. • It shows good thermal reliability after 1000 times heating and cooling cycling. - Abstract: In this paper, a novel form-stable LiNO₃–NaNO₃–KNO₃–Ca(NO₃)₂/calcium silicate composite PCM was developed by cold compression and sintering. The eutectic quaternary nitrate is used as PCM, while calcium silicate is used as structural supporting material. X-ray Diffraction (XRD) shows the PCM and the supporting material have good chemical compatibility. This composite PCM has a low melting point (103.5 °C) and remain stable without decomposition until 585.5 °C. Moreover, this composite shows excellent long term stability after 1000 melting and freezing cycles. Thermal conductivity of the composite was measured to be 1.177 W m⁻¹ K⁻¹, and that could be increased by adding thermal conductivity enhancers into the composite. Meanwhile, microstructure of the composite PCM is observed by scanning electron microscopy (SEM). Latent heat and heat capacity of the composite are measured by differential scanning calorimetry (DSC). This composite PCM with low melting temperature, high thermal conductivity and excellent stability could be used as a new PCM for mid-low temperature thermal energy storage (TES) system.