A core-shell structured PCM with Na₂SO₄ encapsulated by SiO₂ for high temperature thermal storage

In latent heat thermal storage, macro- or microencapsulation of phase change materials (PCMs) can benefit PCM performance. This work proposed a novel chemical method for microencapsulation of inorganic PCM for high temperature thermal storage. This method encapsulates Na2SO4 (PCM) with SiO2 shell via the sol-gel technique. The SiO2 shell is a fire-resistant material and can effectively inhibit the liquid leakage during solid-liquid phase change process. Comprehensively considering the thermal conductivity, thermal stability, melting temperature, and latent heat, the silica mass fraction has been optimized at 5.4% of the composite. In this encapsulation, silica particles were observed decorated on the surface of large Na2SO4 particle and perfect core-shell structures were obtained for the nano-size Na2SO4 particle. The thermal conductivity of the encapsulated Na2SO4@SiO2 has been enhanced by 21% compared to pure Na2SO4 at 800^oC. The initial phase change temperature, peak temperature and latent heat of this encapsulated PCM are 885.2 ^oC, 887.9 ^oC and 170.6 J/(g. K), respectively. The TG/DSC shows that this PCM has almost no mass loss (<1 %) under calcination temperature of 1000^oC. Thermophysical properties of the encapsulated Na2SO4@SiO2 varied marginally after 50 thermal cycle tests.