Novel Na₂SO₄@SiO₂ phase change material with core-shell structures for high temperature thermal storage

Microencapsulated composite material using Na₂SO₄ as core and SiO₂ as shell for high temperature thermal energy storage is prepared. The effects of silica mass percentages within the Na₂SO₄@SiO₂ PCM composites on thermal conductivity, thermal stability, melting temperature, and latent heat are investigated. No new phases are formed during the encapsulation process. The spherical silica nanoparticles with diameters at around 300 nm are well decorated on the surface of Na₂SO₄. The PCM composite with 5.4% silica addition is determined as the optimal sample due to its excellent comprehensive properties. The inhibition of liquid leakage during melting can be effectively realized. The thermal conductivity of Na₂SO₄@SiO₂ PCM under high temperatures (600–800 °C) can be increased to 0.59 W/(m K), 0.62 W/(m K), and 0.87 W/(m K), respectively. The initial and peak melting temperatures of the Na₂SO₄@SiO₂ are tested at 885.20 °C and 887.91 °C, respectively. The latent heat is determined as high as 170.6 J/(g K), and the total heat storage density including latent and sensible heat with a temperature span of 100 °C is 390.6 J/g, and the mass loss is observed < 1% under 1000 °C. In addition, the latent heat loss percentage after 50 thermal cycle tests is ≤ 4.3%.