Preparation and characterization of sodium sulfate/silica composite as a shape-stabilized phase change material by sol-gel method

A sodium sulfate (Na₂SO₄)/silica (SiO₂) composite was prepared as a shape-stabilized solid-liquid phase change material by a sol-gel procedure using Na₂SiO₃ as the silica source. Na₂SO₄ in the composite acts as a latent heat storage substance for solid-liquid phase change, while SiO₂ acts as a support material to provide structural strength and prevent leakage of melted Na ₂SO₄. The microstructure and composition of the prepared composite were characterized by the N₂ adsorption, transmission electron microscope (TEM), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction. The results show that the prepared Na₂SO₄/SiO₂ composite is a nanostructured hybrid of Na₂SO₄ and SiO₂ without new substances produced during the phase change. The macroscopic shape of the Na₂SO₄/SiO₂ composite after the melting and freezing cycles does not change and there is no leakage of Na ₂SO₄. Determined by differential scanning calorimeter (DSC) analysis, the values of phase change latent heat of melting and freezing of the prepared Na₂SO₄/SiO₂ (50%, by mass) composite are 82.3 kJ·kg^-1 and 83.7 kJ·kg^-1, and temperatures of melting and freezing are 886.0 C and 880.6 C, respectively. Furthermore, the Na₂SO₄/SiO₂ composite maintains good thermal energy storage and release ability even after 100 cycles of melting and freezing. The satisfactory thermal storage performance renders this composite a versatile tool for high-temperature thermal energy storage.