Synthesis and thermal properties of novel sodium nitrate microcapsules for high-temperature thermal energy storage

- A novel NaNO3 microcapsule was prepared for high-temperature thermal energy storage.
- The microcapsule consists of perhydropolysilazane as the shell and NaNO3 as the core.
- The melting point and latent heat are about 306 ℃ and about 159 J/g, respectively.
- The microcapsule has stable microstructures and properties at high temperature.

Perhydropolysilazane (PHPS), a ceramic precursor resin with outstanding high-temperature resistance, was used as the shell material to prepare novel sodium nitrate microcapsules (MCP-NaNO3) for high-temperature thermal energy storage. The microstructure and thermal properties of the MCP-NaNO3 were investigated by DSC-TG, SEM, FTIR, EDS, etc. The MCP-NaNO3 presented a melting point of 306.19±0.10 ℃ and latent heat of 159.2±2.4 J/g. The MCP-NaNO3 had a thin shell, and the weight percentage of NaNO3 in the MCP-NaNO3 was calculated to be about 85 wt%. The melting point of MCP-NaNO3 almost had no change, and the supercooling of MCP-NaNO3 only had a small increase of about 2.69 ℃ compared with that of NaNO3. The thermal decomposition temperature of NaNO3 in the MCP-NaNO3 was enhanced more than 36 ℃, up to 647.60 ℃. The PHPS shell was able to ensure the MCP-NaNO3 to be still granular after heated at 350 ℃, and the melting point and freezing point of the MCP-NaNO3 were almost invariable. The MCP-NaNO3 developed in this study has great promise in future energy and chemical processes. The method that using ceramic precursor resins as microcapsule shells paves a new way to prepare various high-temperature phase change microcapsules.

The novel sodium nitrate (NaNO3) microcapsules consisted of perhydro polysilazane (PHPS) as the shell material and NaNO3 as the core were prepared by solvent extraction and ultrasonic dispersing processes for high-temperature thermal energy storage. The microcapsules, whose melting point is about 306 ℃, have stable microstructure and thermal properties at the high temperature of 350 ℃.321