Preparation and characterization of hydrated salts/silica composite as shape-stabilized phase change material via sol-gel process

A novel shape-stabilized phase change material composite was prepared by impregnating the mixture of hydrated salts (Na₂SO₄· 10H₂O-Na₂HPO₄·12H₂O) into porous silica matrix obtained by sol-gel process and further coated with polyvinylpyrrolidone (PVP) to improve the thermal cycling performance. The chemical compatibility, morphology and phase change properties were investigated by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), hot-stage polarizing optical microscope (HS-POM) and differential scanning calorimetry (DSC). Confined in the silica matrix, phase segregation of the hydrated salts was inhibited and subcooling was slightly mitigated. No leakage was observed during the solid-liquid phase transition even when the mass ratio of hydrated salts to silica was as high as 70:30. Results showed that the melting enthalpy of the composite can reach 106.2 kJ/kg with the melting temperature at 30.13 °C and there was no significant enthalpy loss after 30 thermal cycles.